Recent Comments

Prev  2608  2609  2610  2611  2612  2613  2614  2615  2616  2617  2618  2619  2620  2621  2622  2623  Next

Comments 130751 to 130800:

130751. Patrick 027 at 13:30 PM on 3 November 2008
        Arctic sea ice melt - natural or man-made?
        Eddy fluxes - and the QBO!: One way to look at momentum transfer by waves is form drag. Another way is to look at the eddy flux of the wave. Take any variable, q. the total state q = average q + q', where q' is the perturbation, which must average to zero along the same dimension(s) over which q was averaged to get average q. The product of two eddy quantities, such as u'v', can be averaged, and this average may be nonzero if there is a correlation between u' and v' even thought the average of each is zero. In the case of vertically propagating gravity waves, because of the slantwise perturbation motions (relative to basic state wind), there is a correlation between u' and w' (w is the vertical speed - earlier I used w for angular frequency; that choice was made because w looks like the greek letter 'omega' which is often used for that quantity. w is generally used for the z-component of velocity. Be aware omega also has dual use; it is the vertical motion in pressure coordinates, the rate of change of pressure over time following the motion (omega = Dp/Dt; w = dz/dp * omega; negative omega is upward (positive w))). Thus gravity waves have an average u'w' - averaged over horizontal distance, this is the eddy vertical transport of zonal momentum (per unit mass) at that level. The same can be done with equatorial Kelvin waves, which have similar phase line and group velocity relationships in the zonal direction; but equatorial Kelvin waves can only propagate to the east relative to the air. This can also be done with equatorial Rossby-gravity waves (which only propagate to the west relative to the air), but with a catch. The average u'w' of Rossby-gravity waves does not agree with the form drag - in fact it's the wrong sign. The key to resolving this is that Rossby-gravity waves also have a nonzero average of v'T' - the eddy northward temperature flux. This contributes to an EP flux which can be anylized to figure out what the momentum transfer by these waves actually is. But it's easier to visualize the form drage acting on wavy material surfaces. Vertically propagating equatorial Kelvin waves and equatorial Rossby-gravity waves are able to transfer eastward (westerly) and westward (easterly) momentum upward to the stratosphere, respectively. But what happens to their momentum fluxes/wave stresses? I think, similarly to gravity waves (?): Holton, p.427: "It was pointed out in Section 12.4 that quasi-geostrophic wave modes do not produce any net mean flow acceleration unless the waves are transient or they are mechanically or thermally damped. Similar considerations apply to the equatorial Kelvin and Rossby-gravity modes. Equatorial stratospheric waves are subject to thermal damping by infrared radiation and to both thermal and mechanical damping by small-scale turbulent motions." And then: "Such damping is strongly dependent on the Doppler-shifted frequency of the waves." I believe that refers to the frequency following the air flowing through the waves. "As the Doppler-shifted frequency decreases, the vertical component of group velocity also decreases, and a longer time is available for the wave energy to be damped as it propagates through a given vertical distance." And then: "Thus, the westerly Kelvin waves tend to be damped preferentially in westerly shear zones, where their Doppler-shifted frequencies decrease decrease with height. The momentum flux convergence associated with this damping provides a westerly acceleration of the mean flow and thus causes the westerly shear zone to descend." Rossby-gravity waves, by the same logic, are damped more in easterly shear zones and cause easterly acceleration of the mean flow and thus cause easterly shear zones to descend. If we have weakly westerly flow to start with with some westerly shear, the Kelvin waves will be damped out sooner during upward energy propagation, and their westerly acceleration will be concentrated at lower levels; meanwhile the Rossby-gravity waves' easterly acceleration is not distributed as such. Thus the mean zonal wind becomes more westerly especially at lower levels and somewhat more easterly at upper levels. (PS here, upper and lower are completely relative; this could all be in the stratosphere.) This intensifies the westerlies and the westerly shear beneath them and brings these to lower levels, concentrating and limiting the vertical extent of Kelving wave propagation and the westerly acceleration they induce, while producing an easterly shear zone above the westerlies where Rossby-gravity wave damping is enhanced. This strengthens the easterlies at upper levels. As the westerlies descend, the easterlies increase in strength and descend. Eventually the easterlies may push the westerlies into too thin a layer (?), or crowd them out by pushing them down (below the tropopause) where other forces keep the zonal wind from varying in the same way (?) (see Holton pp. 428-429). As that happens the Kelvin waves are no longer damped so much at the lower levels and are not blocked from reaching upper levels again. Etc. In this way, vertically propagating equatorial Kelvin and equatorial Rossby-gravity waves can drive the QBO - the quasi-biennial oscillation. The QBO is a repetative reveral of the zonal winds in the equatorial stratosphere; it has a period of around 24 to 30 months (Holton p.424). New phases form above 30 km height and propagate downward at around 1 km per month, the propagation occurs without weakenning (attenuation) down to 23 km, but quickly weakens thereafter (Holton p.425). The variation in zonal (east-west) winds is zonally symmetric (doesn't vary much over different longitudes) and is symmetric about the equator, with a maximum amplitude of ~ 20 m/s and "an approximately Gaussian distribution in latitude with a half-width of about 12[deg]," (Holton, pp.424-425). Holton p.424: The QBO is the closest thing found to being a regular periodic atmospheric cycle that is not driven by a periodic forcing. ___________________ The comment 294 website does at at least one point distinguish between eddies and waves. I think the line between them is a matter of perspective and purpose. When looking at the fluxes by waves without resolving individual waves, but rather by looking at the average flux as in v'T' or u'w' or v'q', u'v', etc., these fluxes are referred to as eddy fluxes. When looking explicitly at resolved phenomena at some range of spatial scales, unresolved motions that may produce mixing or fluxes would be called unresolved eddies. The more familiar kind of turbulence is associated with a familiar kind of eddy-viscosity and eddy-mixing (which dominates over molecular viscosity and molecular mixing in most of the atmosphere except in the thinnest layer immediately next to the surface and then I would guess also at very high levels where the density is extremely low; I know that at least for mixing, molecular starts to dominate over eddy at somewhere around - I think 100 km, roughly - this is called the turbopause and marks the top of the homosphere and the bottom of the heterosphere.). This viscosity acts like any normal friction to make the fast slow and the slower faster if next to something fast, etc. On larger scales, different kinds of eddies might be considered to have a negative viscosity associated with them, depending ... (?) Perhaps one way of considering waves and eddies as being different is if waves induce actual waves in the contours of some conserved quantity while eddies have closed loops of such contours. Alternatively, and not necessarily corresponding to the former, one could distinguish between wind fields with wavy strealines and those with closed loop streamlines. Then again, if one uses a frame of reference that follows either the mean wind or some structure (however it propagates relative to the wind), one could distinguish between wavy open trajectories and closed trajectories. PS If a pattern of alternating cyclonic and anticyclonic streamlines is propagating through the air to the east, so that relative to the structures, the air is flowing through these structures to the west, then, if the structures have weak amplitudes, the trajectories are deflected but remain open-ended (being wavy). In the northern hemisphere the trajectories would deflect south around anticyclones and north around cyclones. As the amplitude is increased (or the propagation speed through the air is decreased), however, one would start to get closed trajectories. This would start south of the center of the cyclone and north of the center of the anticyclone.
130752. Patrick 027 at 11:51 AM on 3 November 2008
        Arctic sea ice melt - natural or man-made?
        "the group velocity is actually the velocity of an interference pattern" Specifically the group velocity moves with the amplitude variation pattern (associated with a 'beat frequency'). "if winds are tending to approach geostrophic balance, then the propagation of Rossby waves may be slowed because the contours of barotropic PV have to move farther than the contours of AV," Because if the AV were conserved, waves in the AV contours could create ageostrophic winds. Postivive geostrophic AV anomalies tend to correspond to relatively lower pressures; the coriolis force tends to act on a positive ageostrophic AV anomaly to cause horizontal divergence, which lowers the pressure and also the AV (if preserving PV), bringing them closer to geostrophic balance with each other. This effect may be reduced if much of the AV gradient is from a relative vorticity gradient, in which case the PV contours may bring some pressure variation along with them that would reduce the ageostrophic portion of the wind. But this may or may not actually be what happens (?)- the relationship of vorticity and pressure is most obvious when there is an actual maximum or minimum, as opposed to a extensive gradient. (However, - in the frame of reference following the basic state wind, curvature of streamlines associated with the wave will add a centrifugal force, which would increase the divergence from growing positive AV anomalies but decrease the convergence in a growing negative AV anomaly.) Would the effect change when the AV is large?; in that case less divergence or convergence would be required to produce a unit change in AV (especially for reducing pressure for a positive AV anomaly)... ----------- PS in case it wasn't clear, the generalization of Rossby waves in any vorticity gradient is that they tend to propagate with higher potential vorticity to their right - north as described above is analogous to the direction of the potential vorticity gradient in general... --- The comment 294 website mentions that a weak vortex may break up and radiate Rossby wave disturbances. A stronger vortex wouldn't do so to the same degree. Why? I suspect it's because a strong vortex might be such that in the total state, some AV or PV contours might form closed loops, or more generally be distorted in some way other than simple nearly sinusoidal forms. In the barotropic case, if there is no mixing and a a quantity is conserved following the motion, closed loop contours of that quantity can never merge with other contours of the same value. In three dimensions and for baroclinic situations, replace contours with surfaces. PS I started to try to draw this out and got the impression that the vorticity anomaly would wobble about itself in the same direction as it's wind field. I think I've read something to that effect. Aside from fluid motion itself, another way to get variations in barotropic PV besides beta (df/dy) is variations in fluid depth. One source of such variation can be the topography of the bottom surface. There will thus tend to be a barotropic PV gradient towards mountain ranges and plateaus in the atmosphere. As pointed out in the comment 294 website, the topography in the northern hemisphere in particular tends to force Rossby waves which are somewhat barotropic (though they also do vertically propagate into the stratosphere and thus allow dynamically-induced high pressures pressing into the west sides of mountainous areas to slow the westerly (eastward) momentum of upper levels. There can be resonance with the wavelength of this forcing with Rossby waves whose phase speeds are such that, for the given wind, they would (without forcing) tend to propagate through the air to almost be stationary with respect to the surface.
130753. chris at 10:03 AM on 3 November 2008
        Water vapor is the most powerful greenhouse gas
        Well yes those are very errant thoughts! The CO2 stays in the atmosphere as a well-mixed gas. The water vapour just comes out again, since its concentrations are entirely dependent on the air temperature and pressure. It's easiest to see this by considering what happens in the short term. If atmospheric CO2 levels are increasing by 2 ppm per year, say, then every day (on average) an amount equivalent to around 0.005 ppm of excess CO2 is retained in the atmosphere. That's pretty small. Over a couple of weeks the atmosphere comes to equilibrium in relation to water vapour (perhaps even more quickly in relation to the near-ground level regions of the atmosphere where the water vapour is released). So as atmospheric CO2 levels rise relentlessly week on week, month on month, year on year, atmospheric water vapour reaches a rapid equilibration according to its vapour pressure in relation to the atmospheric presure and temperature. If this takes a week, the net "steady state" addition of water vapour is something like 7 x 0.005 x 10 x 2 of ppm CO2 "equivalents" (taking your value of the relative power of H2O compared to CO2, which actually I think is incorrect anyway, and taking account of the fact that so far only around 1/2 of the CO2 we emit stays in the atmosphere). So even within your scenario any excess water vapour resuting from burning fossil fuels produces a trivial excess warming - something well under that of 1 ppm of additional CO2. And of course it's a "steady state" value (both within your scenario, and likely in reality too), so you only add it once, whereas the atmospheric CO2 concentrations continually rise and rise... One might use your argument in reverse. As trees/plants grow they pull CO2 and water vapour out of the air: 6CO2 + 6H2O ----> (CHOH)6 + 6O2 where (CHOH)6 is generic carbohydrate During the N. hemisphere plant growth season, this is pulling more water vapour out of the air than is being released from burning fossil fuels I suspect. And in the autumn/winter months when N. hemisphere plant decay is "pumping" CO2 and water vapour back into the atmosphere, massively supplementing the water vapour released during oxidation of fossil fuels... ..but we don't find massive cycles of atmospheric water vapour concetrations for the reasons outlined above. I have a feeling that the only significant anthropogenic addition of water vapour to the atmosphere is from airlines at high altitude where the water vapour has a far higher residence time.
130754. Patrick 027 at 06:13 AM on 3 November 2008
        Arctic sea ice melt - natural or man-made?
        Thanks Philippe!
130755. Mizimi at 06:00 AM on 3 November 2008
        Water vapor is the most powerful greenhouse gas
        some errant thoughts..... Burn methane (CH4) and you get CO2 + 2H2O Ethanol (C2H5) gives 4CO2 + 5H2O Propane (C3H8) gives 3CO2 + 4H2O Benzene (C6H6) gives 6CO2 + 3H2O. Alkane hydrocarbons follow the formula C(n) H (2n+2) .... Heavy oils, for example, C18H34 give 18CO2 + 17H2O Since water vapour is around 10x more powerful a GG than CO2, it follows that the WV produced by burning gas and oils has a greater immediate warming effect than the CO2. Whilst generally it is held that the WV condenses out within a period of 14days, it is of course being continuously replaced so that its effect is more or less continuous. As the usage of oil and gas increase so the amount of water vapour added to the atmosphere also increases, as does the overall warming effect. According to WorldWatch, in 2005 we burnt some 3800M tons of oil and 2200M tons (oil equivalent) of gas, making a total of 6000M tons of FF excluding coal. Crudely speaking, we put as much WV into the air as we did CO2 ......but since it is 10x more effective a GG most of the warming actually must be coming from WV, not CO2.???? In addition, we are pumping lots of WV into the atmosphere through other activities.. Drax power station (UK) is a coal fired station that uses evaporative condensers..cooling towers...which take water from a local river. Of 59M tons of water taken annually, only 29M tons are returned to the river, the rest goes into the atmosphere.....the equivalent of 310M tons of CO2 or 0.01% of the 27,000M tons of CO2 emitted globally. From ONE power station. www.draxgroup.plc.uk/files/page/916/Drax_environmental_performance_review_2003.pdf Comments please???
130756. Philippe Chantreau at 03:20 AM on 3 November 2008
        Arctic sea ice melt - natural or man-made?
        You really love this stuff Patrick, don't you? It's good to have people like you around :-)
130757. Patrick 027 at 13:37 PM on 2 November 2008
        Arctic sea ice melt - natural or man-made?
        I should say: barotropic PV is conserved when there is no friction and no mixing (although mixing tends to occur with friction). When there isn't mixing, contours (or corresponding surfaces in three dimentions) of conserved quantities, such is IPV for inviscid adiabatic motions, can serve as material lines (or surfaces).
130758. Patrick 027 at 13:33 PM on 2 November 2008
        Arctic sea ice melt - natural or man-made?
        One more note for now: barotropic Rossby waves with divergence: I mentioned above isentropic PV. There is also barotropic PV, which is the absolute vorticity divided by the fluid depth in the case of incompressible fluid (nearly the case for water) (in the case of the atmosphere, I think surface pressure would be a good stand in; barotropic PV = AV/surface pressure). When the fluid motion is constant with height, so that any divergence is constant with height, then under conditions where barotropic PV is conserved (no friction), AV increases or decreases so that AV is proportional to surface pressure. When planetary vorticity is constant (when the wind has no north-south component), then changes in AV must correspond to changes in relative vorticity and thus the wind field. ... to be continued, but to make a long story short, if winds are tending to approach geostrophic balance, then the propagation of Rossby waves may be slowed because the contours of barotropic PV have to move farther than the contours of AV, and the anomaly wind is proportional to the AV anomaly amplitude. Before going through the math, I'm expecting this would be a relatively smaller factor where AV is larger. It might also be smaller when the AV gradient is due more to the relative vorticity gradient - that is, when beta is smaller.
130759. Patrick 027 at 12:19 PM on 2 November 2008
        Arctic sea ice melt - natural or man-made?
        The website in comment 294 actually has so much information that I probably don't need to say much more about Rossby waves myself. I will add a few points though. --- For a given wavelength, if the phase lines are tilted at an angle G from parallel to the basic state vorticity gradient (or from perpendicular to the basic state AV contours, and again for simplicity let's keep those aligned east-west (x direction), with the vorticity gradient to the north (positive y direction)), then: The component of the anomaly wind parallel to the basic state AV gradient, or the component of the basic state AV gradient that is parallel to the anomaly wind, is proportional to cos(G). Thus the phase speed relative to the wavelength varies with cos(G). In this case the phase speed is in the direction perpendicular to the phase lines, and is thus at an angle G from due west. It is both the inverse of the phase speed and the inverse of the wavelength which have components that add as vectors; the wavelength measured along the x direction is inversely proportional to cos(G), and so the phase speed in the x direction actually remains constant (it is equal to the phase speed perpendicular to the phase lines, times the ratio of the wavelength in the x direction to the wavelength measured perpedicular to phase lines; this ratio is equal to the magnitude of the wave vector divided by the zonal wave number (M/k) - **I'm designating the wave vector as M instead of K so it's easier to distinguish from the lowercase k denoting the zonal wave number ). --- (PS you might wonder if it really works that way, because: when the phase lines are parallel to the y axis, the spacing of total AV contours remains constant in the y direction even when the anomaly AV is added to make the contours sinusoidal. But when the phase lines are tilted, the contours are no longer sinusoidal - they are distorted. However, the spacing measured in the direction parallel to phase lines remains the same (think about how far along such an angle one must move the contour when adding a vorticity anomaly A - it will be proportional to A/[B*cos(G)] ), and this is the direction of the anomaly wind which moves those contours back and forth. So it works. (The anomaly wind W produces new anomaly vorticity at the rate W*B*cos(G), and again W is proportional to A*L, and the wave propagates a distance L at a rate proportional to W*B*cos(G)/A, so the phase speed (perpendicular to phase lines) is proportional to L*W*B*cos(G)/A = L*A*L*B*cos(G)/A = L^2 * B*cos(G) ------- The frequency is equal to the phase speed divided by the wavelength, and the angular frequency w is equal to 2pi times that: w = 2pi*L^2*B*cos(G)/(L*2pi) = L*B*cos(G) where I included the constant 1/(2pi) from the phase speed equation from Holton to make the relationship. precise. (I hope you don't mind me using the same symbol for the wave vector and for it's magnitude:) M = 2pi/L w = 2pi*B*cos(G)/M the zonal wavenumber k = M*cos(G) the meridional wavenumber l = M*sin(G) w = 2pi*B*k/(M^2) = 2pi*B*k / (k^2 + l^2) The group velocity cg: the x component is equal to dw/dk the y component is equal to dw/dl dw/dk = 2pi*B/ (k^2 + l^2) - 2k * 2pi*B*k / (k^2 + l^2)^2 = 2pi*B*[ (k^2 + l^2) - 2*k^2 ]/(k^2 + l^2)^2 = 2pi*B* (l^2 - k^2) / (k^2 + l^2)^2 dw/dl = - 2l * 2pi*B*k / (k^2 + l^2)^2 = - 2pi*B*(2*k*l) / (k^2 + l^2)^2 And except for the wrong sign on dw/dl, and an extra factor of 2pi, I've gotten the mathematical expressions in Holton, p.344. Is Holton wrong or am I wrong? Well, it's possible I should have put a negative sign in the formula for w because if the phase movement is always to the west, then k should be negative - although I've seen wave vectors pointing in the opposite direction of phase propagation in one or more diagrams... Anyway, that website from comment 294 has more info about group velocity. It uses a graphical representation, where contours of w are plotted over k,l space. Placing the same graph in x,y space, the group velocity vector then is always perpendicular to w contours (in order to be parallel to the w gradient) and points toward higher w (toward the interior of the contour-confined spaces in this case) and the magnitude of the vector is proportional to the w gradient magnitude (inversely proportional to the w contours, provided that each contour marks the same change in w relative to the next or previous contour). ------- Instead of an infinite series of waves, what happens if there are a few crests and troughs. Take just a line vorticity anomaly, for example. Perhaps, as before, It's wind field will tend to propagate that vorticity anomaly to the west (and possibly north or south depending on angles). But perhaps it will also create a new vorticity of opposite sign in it's wake. It may get a bit tricky because for a single vorticity anomaly of one sign, the wind field on either side must extend to infinity. In order to constrain the winds, one must have an average zero vorticity in the anomaly field. In that case one could consider a single whole wavelength of the vorticity anomaly including a whole crest and a whole trough. The wind field in that case is sinusoidal but either it's maxima or it's minima is zero - not it's average. It will thus tend to pull the phase of the vorticity wave farther east toward the middle and enlarge it while pushing the other phase of vorticity away and reducing it. The new vorticity anomaly will however tend to induce a wind field that extends on either side to infinity. However, it might instead be possible to find a solution where the new wind field is producing a third vorticity anomaly such that the new wind field can be spatially constrained ?? Of course, if the amplitudes are weak enough, an approximation can be made to ignore wave-wave interaction, and then whatever the original disturbance is, it can be decomposed into a linear superposition of some spectrum of waves. And each part of that spectrum can act independently - the extent of the disturbances associated with each part of the spectrum (which may be a two-dimensional spectrum, with both k and l varying) will propagate with it's group velocity but within that extent, phases will propagate with their phase speeds and directions. And with nonlinear wave interaction when the waves have sizable amplitudes? That will have to be another day. (PS if I'm not mistaken, the group velocity is actually the velocity of an interference pattern that would be made by the wave in question and other waves that are only infinitesimally different in k and l. What about the interference patterns produces by waves that are significantly different in k and l? Would each have it's own group velocity and then an interference pattern with it's own velocity? What happens if a third wave's phase motion, or it's group velocity, matches the motion of the interference pattern of the other two? I don't know much about this, but I'd expect nonlinear interaction among two waves to be strongest when they are similar in wavelength (if not direction??). Very short wavelengths would just propagate through the 'basic state' created by very long wavelengths, and very long wavelengths (I'm guessing) wouldn't interact with or scatter much from very small disturbances (although a fine scale structure could have a macroscopic effect, but that would just be by altering the basic state ... (if I had time: An analogy to optical index of refraction and details much smaller than a wavelength))... I have heard of something called nonlinear triad resonance, which I think is when three waves have wave vectors whose vector sum is zero (they form a triangle)...
130760. Mizimi at 08:46 AM on 2 November 2008
        Animals and plants can adapt
        England: Little egrets have been observed nesting (previously seen but in winter migrated to southern Europe/Africa) and in 2008 cattle egrets ( from Africa) have also been filmed, although not nesting. In S.England green lizards and brown rock lizards, both mediterranean species are now resident. An illustration of species movement as conditions allow. ( and in the case of the lizards, ably assisted by transcontinental traffic)
130761. chris at 08:03 AM on 2 November 2008
        Water vapor is the most powerful greenhouse gas
        Re #11 What point are you trying to make Mizimi? It seems a little like that specious argument that used to be made against seat belts, that use of the latter prevented occupants from being "thrown clear" in an accident. Atmospheric water vapour is a greenhouse gas whose increased atmospheric concentration enhances the Earth's surface temperature. Of course the evaporation of water from the ocean surface results in transfer of the heat of evaporation into the atmosphere..it's a major mechanism by which solar thermal energy is transferred from the equatorial regions to the high latitudes....some of the thermal energy is radiated into space... But overall, raised atmospheric water vapour results in an increase in the Earth's surface temperature. As we've just seen (posts # 9/#10), water vapour amplifies the warming resulting from whatever forcing caused the atmosphere to warm in the first place! Water vapour is a positive feedback in the Earth's global energy budget....
130762. chris at 07:40 AM on 2 November 2008
        Do 500 scientists refute anthropogenic global warming?
        Re #3 That's not real a good description of science. On reading a new paper one should ask: (i) Does the data justify the interpretations? (ii) What implications does this evidence have for the particular issue under study? (iii) Does the paper stimulate me to address the issues with new experiments and what might these new experiments be? Note that the issue of "falsification" is much better addressed during the process of experimentation and observation that lead to the preparation of the paper. Indeed that's where "falsification" should be addressed, and it's a major part of the peer-review process in pukka scientific journals to ensure that this is done properly. Initial observations should be addressed with appropriate control experiments. Alternative explanations of observations should be tested with appropriate experiments. Notice that your comment about "tribes" is unjustified and doesn't relate very well to real science. It's more of a political allusion. There aren't really any "tribes" in the science (of course all scientists make a personal investment in their particular ideas and hypotheses, and sometimes these can give rise to a certain set of more widespread preferences in ill-defined research areas). In general there is only the science and its evidence. The notion of "tribes" is a construct of those that wish to create the illusion of controversy or uncertainty where this might not exist...
130763. chris at 07:22 AM on 2 November 2008
        Comparing IPCC projections to observations
        #32 Surely if we're being skeptical, we want to know the whole story and shouldn't be fobbed off with allusions and sly aspersions followed by "No comment". Of course we might question the Mauna Loa atmospheric CO2 data. And so we should. But let's do it properly. There are dozens of stations in remote locations around the world measuring atmospheric CO2 levels. We can examine the atmospheric CO2 measured at the South Pole, at Assekrem in Algeria in the N. Sahara, at Easter Island, and so on... In fact we find that each of these locations, and many more, give atmospheric CO2 readings (averaged globally to account for the N hemispheric plant growth/decay seasonality and atmospheric gas diffusional mixing) that are rather similar atmospheric CO2 readings... ...so your allusions about the Mauna Loa readings are unjustified.... ..let's be skeptical...but let's also be thorough and honest!
130764. chris at 06:39 AM on 2 November 2008
        Models are unreliable
        Re #61 Dan’s pursuing another error that results from not bothering to find out what the term "feedback" means in an unfamiliar field. The mistake is easy to see in Dan’s definition of "feedback". Here it is: [Dan: "Feedback means that the output (results, response) influences the input."] But that definition doesn't really apply to the climate system and its temperature inputs/outputs in relation to the energy balance that defines an equilibrium temperature. Here's a simple example. The solar output increases a tad (perhaps during the solar cycle). As a result the atmosphere warms a bit. What might also happen? Since the relative humidity of the atmosphere tends to remain constant, and a warmer atmosphere has a higher saturation point for water vapour, the atmospheric water concentration rises (we can measure this in the real world). This is considered a positive feedback in atmospheric physics. Does this accord with Dan’s definition of "feedback" as used in engineering? Not really. I think we’d all agree that the enhanced water vapour concentration doesn't alter the solar output. Of course there is an element of "engineering"-style "feedback" in the water vapour feedback. The solar warming results in raised water vapour concentration which warms the atmosphere further resulting in further enhanced water vapour concentration. If the solar change results in a 1 oC change, and the resulting water vapour feedback adds an additional x of additional warming then the total warming from the solar enhancement + water vapour feedback is something like 1 + x + x^2 + x^3 + x^4 ... which is 1/(1-x). We can make the same argument for the enhancement of atmospheric CO2 concentrations. If the atmospheric CO2 concentrations rise by an amount giving a 1 oC of warming then the water vapour feedback will result in a total warming of 1/(1-x), where x is the temperature rise at equilibrium resulting from the enhanced water vapour concentration that is induced by a CO2-driven rise in temperature of 1 oC. Again note that in this case (enhanced CO2 forcing a temperature rise that generates a positive water vapour feedback), Dan’s “engineering-style feedback” barely applies (it might a tad). In other words, the water vapour feedback doesn’t recruit further rises in atmospheric CO2. Note that this is a little different from the CO2 feedback warming from enhanced insolation, for example during glacial-interglacial transitions driven by Milankovitch cycles. Here the enhanced insolation results in atmospheric warming which recruits a small amount of CO2 from the ocean and terrestrial environment, which results in a small amount of enhancement of the water vapour concentration with a tiny additional enhancement of the atmospheric CO2. But we know that the temperature-dependent recruitment of CO2 into the atmosphere is quite small. So, for example, the last glacial-interglacial transition from around 15000-10000 years ago resulted in a global temperature increase near 6 oC, and a warming-induced increase in atmospheric CO2 of around 90-100 ppm. So it takes a 1 oC of temperature rise to raise atmospheric CO2 levels by around 15-16 ppm. Interestingly this takes around 1000 years (averaging over the transition), whereas we’re getting this amount of enhanced CO2 in around 7 years now. Dan suggests that: “If net feedback is positive the trend must continue up at a progressive rate. The effect on a savings account balance with compound interest is a familiar example of net positive feedback. Complexity does not alter how net feedback works.” But each of those statements is untrue in the context of atmospheric physics and the Earth’s energy balance. Even though the net feedback is positive, the “trend” DOESN’T “continue up at a progressive rate “. This is because the feedback doesn’t affect the input in the manner that Dan suggests, (and also because the “strengths” of the feedbacks are not sufficiently large as to cause the system to “continue up at a progressive rate “ - see the pnt about the atmospheric CO2 feedback to Milankovitch warming in the last but one paragraph). What happens is that the Earth’s energy balance progresses towards a new equilibrium with a temperature that is somewhat higher than it would be without feedbacks. It’s not like Dan’s idea of “compound interest” in “a savings account balance”, at all. We can add other feedbacks. Some of these, of course, might well be negative. But we know for example that there is at least one more additional positive feedback. The warming from raised CO2 results in melting of mountain glacial and polar sea and land ice. Since this doesn’t result in very much in the way of recruiting of additional CO2, again this is a feedback that doesn’t influence the input (enhanced atmospheric CO2) to any great extent. So we can treat it much as we did above. It will cause additional atmospheric warming as more solar shortwave infrared is absorbed by the earth and converted into thermal energy. This will warm the atmosphere a bit more, and more water vapour will be “recruited”… ..again the Earth’s “temperature” will settle towards a new equilibrium temperature that is a bit warmer than that resulting only from the enhanced atmospheric CO2 with its water vapour feedback. In effect this will be the Earth’s equilibrium temperature that applies to this particular insolation, with this particular atmospheric CO2 concentration and this particular atmospheric water vapour concentration and this particular albedo. Note that the albedo effect is inherently self-limiting, and this is another example of where Dan’s mis-application of “engineering-style” “theory” to an inappropriate example breaks down. We could discuss this too… Overall, we can examine the paleoclimate record, analyze the warming resulting from Milankovitch-forced glacial-interglacial transitions, analyze the 20th century warming record, determine the atmospheric response to volcanic eruptions, study the theoretical response in computer models and so on….all of these indicate that the Earth’s climate responds to enhanced atmospheric Co2 concentrations with positive feedbacks of the sort described in the preceding paragraphs, such that the Earth’s “energy balance” shifts to a new equilibrium that gives us a higher surface temperature that would result solely from the enhanced CO2 without feedbacks. This new equilibrium temperature is around 3 oC of warming per doubling of atmospheric [CO2].
130765. chris at 23:17 PM on 1 November 2008
        Misinterpreting a retraction of rising sea level predictions
        Re #14 and more generally. There seems to be a bit of nonsense over this. The gloabl temperature of 1998 was lifted by around 0.2 oC above the trend by the strongest El Nino of the 20th century. The temperature of 2005 was statistically indistinguishable from 1998. However this was reached without the "aid" of the massive El Nino warming (e.g. http://data.giss.nasa.gov/gistemp/2005/) So one could say that "global warming stopped in 2005". But why bother?! Since 2005 the solar cycle has been in its waning phase (we're pretty much smack at the bottom now)...we've had a La Nina suppressing temperatures during the early months of this year. As John Cook illustrates internal variations and extrinsinc factors introduce "noise" onto the long term trend. So it's pretty unremarkable that the temperature goes up and down a bit as it rises under the influence of enhanced greenhouse forcing. Probably the next record warm year will occur during the next significant El Nino or two....
130766. chris at 23:09 PM on 1 November 2008
        Misinterpreting a retraction of rising sea level predictions
        Re #12: Quietman, the last 5 million years has shown a slow decrease in temperature. That can be seen here, for example: Lisiecki, L. E., and M. E. Raymo (2005), A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records, Paleoceanography, 20, PA1003. or: http://en.wikipedia.org/wiki/Geologic_temperature_record what data are you loking at?
130767. chris at 22:57 PM on 1 November 2008
        Global warming stopped in 1981... no, wait! 1991!
        Re #13 That's nonsense of course. And what does schoolboy pseudo-psychoanalysis have to do with atmospheric, ocean and radiative physics? It seems a bit "conspiracy theorist" to me! Of course fear isn't "the greatest behavioural driver in mankind". I would suggest that sex, ambition, the imperative to care for our children, the drive for creativity, learning and understanding of our environment and world, and so on, are greater "behavioural drivers"; certainly nowadays... As for "supplant(ing of) rationality", I wonder whether you might have got things rather back to front! One of the reasons that "fear" has lost its impact on our lives is that rationality has increasingly dominated our social strutures during the last several hundred years and especially since the 19th century, when a modern scientific rationality has increasingy been the mainstay of social development. While this has been very beneficial to people living in these social strucutres overall, scientific rationality is rather dangerous for various vested interests, and so major institutional structures have developed, especially in the US, to pursue anti-rational campaigns against various aspects of science (e.g. misrepresenting the science on lead in paint and gas, misrepresenting the science on the dangers of asbestos, misrepresenting the science on the effects of ciggie smoking on morbidity and mortality, misrepresenting the science on the effects of aspirin-taking in children with respect to Reyes syndrome, misrepresenting the science on the effects of passive smoking, misrepresenting the science on the effects of chlorofluorocarbons on high altitude ozone.... ...and now misrepresenting the science on global warming. One of the extraordinary things that comes out of this is the extent to which a large proportion of US citizens have been "politicized" into going along with this rubbish even as it undermines their own better interests. They're willing to be treated as chumps, and to imbibe obvious nonsense fed to them on web sites from the likes of Fred Singer, Roy Spencer, some German schoolteacher (!) and so on (a surprisingly small motley crew of the highly misguided if not downright charlatan). Happily, it seems to me that outside of this "parallel universe" of nonsense, policymakers and individuals in general are behaving entirely rationally and without fear in addressing the rather clear scientific imperative to address the problems of massively enhanced greenhouse gas concentrations. It's sad to see the horrendous real/attempted duping of the US population by the anti-rational (of course they're highly rational in the context of pursuit of their vested interests!). This has had a dreary effect on US sociopolitic in the last few decades, with a remorseless driving up of income and wealth inequality...the associated downward drift in social mobility ....rather dismal population health indicators combined with massive health structure costs and so on... ..you might be interested in reading a new book by Professor Larry Bartles (political economist at Princeton) in which he explores the odd phenomenon of the last few decades in the US in which a large proportion of the US population has been "complicit in its own political fleecing" [***] ...the credulous willingness to be taken in by anti-science nonsense on global warming is just more of the same. [***]The Political Economy of the New Gilded Age by Larry M. Bartels Princeton University Press, Princeton, NJ, 2008 (quote from Robert Grafstein in his review of the book in Science magazine yesterday; 31st October p 681).
130768. Patrick 027 at 15:51 PM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        CORRECTION TO COMMENT 286: "(ps for waves in one dimension, phase velocity = frequency times wavelength: c = f*l group velocity = change in frequency per unit change in wavelength: cg = df/dl the angular frequency w = 2*pi*f, and the wave number k = 2*pi/l, so: c = w/k cg = dw/dk " if cg = dw/dk, then cg = d(2pi*f)/d(2pi/l) = 2pi * df/dl * dl/d(2pi/l) = 2pi * df/dl / d(2pi/l)/dl = df/dl / (1/l^2) = l^2 * df/dl so cg is not equal to df/dl. double check: dw/dk = 2pi df/dk, df/dk * dk/dl = df/dl well you can where this is going...
130769. Patrick 027 at 15:31 PM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        This website gives a very good brief description of some of what Rossby waves do: http://isis.ku.dk/kurser/blob.aspx?feltid=30760
130770. Patrick 027 at 14:59 PM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        " is proportional to -L*W*B/A = -L*(A*L)*B/A = -B*L^2." The exact relationship from Holton, p.218-219: relative to the basic state flow, the westward phase speed -cx: -cx = B/(k^2) k is the zonal wavenumber and is equal to 2*pi/L, so this means: -cx = B*(L^2)/(2*pi). So the proportion I found earlier was correct; the missing constant was 1/(2*pi). I actually interpreted the equation from Holton to fit the situation I considered; the equation in Holton was derived with B = beta (no gradient in basic-state relative vorticity). The equation in Holton was actually derived from the more general situation in which the orientation of the phase lines was left unspecified; in which case: -cx = B/(K^2) where K is the magnitude of the wave vector, so K^2 = k^2 + l^2, where k and l are the zonal and meridional wavenumbers, respectively.
130771. Patrick 027 at 13:31 PM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        So, Consider some sizable region within which there is a gradient in absolute vorticity. The flow is strictly two-dimensional, barotropic, invariant in height, and non-divergent. To simplify farther (results will be generalizable but this will make the explanation more clear), assume the wind is everywhere parallel to absolute vorticity contours, which are assumed straight and parallel. Set aside the curvature of the Earth; let the flow be on a flat x,y plane. (absolute vorticity will now be AV to save space here, relative vorticity will be RV) Also assume that the AV gradient is constant, which means the AV contours are equally-spaced. Again, for simplicity, assume AV contours are aligned in the x direction (east-west), so that the AV gradient is north south - and let the AV be increasing toward the north (positive y direction). Let the magnitude of the AV gradient be B. Notice all this implies that the relative vorticity (RV) is entirely shear vorticity. That's not really important to the overall concept, though. The state just described is the basic state. It has basic state AV and RV and basic state winds. Now lets linearly superimpose an AV anomaly (perturbation) field. Note that the AV anomaly is equal to the RV anomaly, because planetary vorticity is entirely included in the basic state; for all practical purposes, planetary vorticity is set, and thus never anomalous or perturbed. This means the entirety of the AV anomaly must be used to determine the anomaly wind field. To start, lets consider an AV anomaly that is sinusoidal in x and constant in y. This is a series of infinite length linear regions of alternating positive and negative vorticity - the crests and troughs of a vorticity wave. In order for the vorticity wave pattern to exist, in between the crests and troughs are wind anomalies, which blow north and south. The anomaly wind blows to the north where west of a vorticity trough (negative vorticity anomaly) and east of a vorticity crest, and blows to the south in the opposite part of the wave pattern. Remember that, in this situation, AV is conserved following the motion. The basic state wind is parallel to the basic state AV contours and so can't change the basic state. The anomaly wind is parallel to the anomaly AV contours and so can't change the anomaly. However, the anomaly wind can advect the contours of the basic state AV and the basic state wind can advect the contours of the anomaly AV. But for our purposes, we choose a frame of reference that follows the motions in the basic state, and so for the time being will ignore the basic state wind. Technically this is impossible due to the basic state RV - the wind is not the save everywhere and so the air cannot be followed with the same frame of reference at every position along y. But for now let's just ignore that.** So in the frame of reference we are now using, the anomaly is not being moved by the basic state wind; the basic state wind has dissappeared from our view; but the basic state AV is still real. Here's what happens: The anomalous wind advects the basic state contours to make them sinusoidal. But we keep the basic state the same; the difference is the creating of a new vorticity anomaly. The new vorticity anomaly is 1/4 wavelength to the west of the first vorticity anomaly. As the new anomaly grows, the new anomaly winds now advect the AV contours of the combined first anomaly and basic state. Notice that the first anomaly and basic state combined form sinusoidal AV contours; the winds of the new anomaly, due to the geometry, are precisely in proportion to the first vorticity anomaly and act to flatten the sinusoidal contours of the combined first anomaly and basic state. The result: if we add all anomalies together, we see a wave pattern that is propagating to the west. The full state (basic + anomaly) has sinusoidal contours of AV (PS note that the AV contour has a trough (visually, if north is up) where the AV itself has a crest (positive AV anomaly)). The anomaly wind varies sinusoidally, and is a maximum in between AV crests and troughs, and acts to move the sinusoidal pattern to the west. (We know that the amplitude of the wave is not growing because the anomaly wind is always zero at the maxima and minima of vorticity anomalies). The sinusoidal variations keep the wave form the same (sinusoidal). This is a Rossby wave. How fast does it propagate? If the vorticity wave amplitude is A and the wavelength is L, then the anomaly wind amplitude W is proportional to A*L (I'll go back and find the exact relationship sometime**; for now I'll just look at proportions). The displacments in y of the AV contours of the total state is proportional to A and inversely proportional to B (the basic state AV gradient). The rate of vertical displacements of the contours is proportional to W; The time taken for the wave to propagate relative to it's wavelength will thus be proportional to W*B/A. Multiplying by wavelength to get the phase speed c: c is proportional to -L*W*B/A = -L*(A*L)*B/A = -B*L^2. Thus the phase speed is to the west (hence the negative sign above) and is proportional to B times the square of L; the basic state AV gradient and the square of the wavelength. Next up: what if the wave phases are tilted in the horizontal (at an angle to the y-axis). Then: What if the wave phases don't extend to infinity in each direct in the direction of phase propagation (perpendicular to the pase lines (crests and troughs)). And Then: What if the waves don't extend to infinity along the phase lines? For example, what happens to a single vortex superimposed on the basic state (PS it tends to propagate westward but it may radiate disturbances and move north or south and disappear into the basic state.) That will cover the basics of phase speed and group velocity. After that, we could consider what happens when variations in the basic state wind distort the wave pattern or interact with it. Then we could consider what happens when different waves interact with each other (in the weak amplitude limit, they pass through like linear superimposed waves; but when one has a sizable amplitude, it significantly alters the 'basic state' through which the other is propagating - hence nonlinear interaction). And then what about three dimensions? Substituting conservation of PV for conservation of AV? What about basic state wind shear in the vertical? What about baroclinic waves? Vertical propagation? Etc... (PS I can't actually go into all of that because - well I don't know enough about it yet myself! And then there's the time factor...).
130772. Patrick 027 at 12:17 PM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        PS1: "Thus, PV is higher where static stability is higher, all else being equal. absolute vorticity increases while conserving PV by vertical stretching (in isobaric coordinates) which corresponds to horizontal convergence due to the conservation of mass." Notice this implies that static stability is reduced by vertical stretching. Indeed, this is true, and can be seen easily by considering that a stable lapse rate requires an increase in potential temperature with height. Vertical stretching increases the spacing of isentropic surfaces in height, asymptotically approaching zero vertical gradient in potential temperature, which implies an approach to the dry adiabatic lapse rate. Horizontal convergence near the surface can thus make cumulus convection more likely (provided moisture), for example. PS2: "You might think that this would have profound implications for general circulation properties but it's not really a big deal (other complexities exist...) It doesn't mean that the southern hemisphere has to be identical to the northern hemisphere (even if the winds did not vary with height)..." Of course, because the requirement for symmetry only exists if vorticity is to be confined to such point vortices. Vorticity in the opposite hemisphere can be spread out to whatever degree and still fit with the irrotational circularly-symmetric wind field about the first point vortex out to some distance. Etc...
130773. Patrick 027 at 12:03 PM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        Conservation of vorticity: Following the motion of the air, vorticity is conserved provided that 1. the wind is non-divergent (when vorticity does change significantly, for larger-scale motions at least, the divergence is generally the most important factor. Divergence changes the vorticity because the conservation of angular momentum (in the absence of a torque, see conditions 2 and 4 below in particular) requires a conservation of circulation around an area whose boundaries follow the motion of the air. Positive divergence enlarges such an area, so in order to conserve circulation, the average vorticity (the component perpendicular to the area) decreases, remaining inversely proportional to area. Negative divergence, which is positive convergence, shrinks such an area and thus increases the vorticity with the same mathematical relationship. Notice that the perimeter also tends to grow or shrink (provided the divergence is isotropic (du/dx = dv/dy) or nearly so) so the wind speed tends to decrease or increase, for divergence or convergence, respectively. PS when divergence is anisotropic, or if for whatever other reason, there is deformation, this can change the wind speeds associated with a given amount of vorticity over a given area. The closer the shape of such an area with constant vorticity is to being circular, or the closer the vorticity is to being evenly distributed within a circular shape, the stronger the winds. The more elongated such a shape, the greater the perimeter, thus for the same circulation, the smaller the winds. The effect of course is most important close to the vorticity region - farther away the details of distribution don't matter as much. If a given amount of circulation is spread out more to have a very long perimeter about the same area, it has a reduced effect on the wind field and may act more like a 'passive tracer' (if it is conserved following the motion) than an influential 'source' of the wind. 2. no friction 3. no tilting/twisting of non-vertical vorticity components into the vertical (not a problem for strictly two-dimensional flow). This is generally a minor factor in changes in vorticity, at least for the larger-scale motions of the atmosphere (but it can be very important for severe thunderstorms). 4. no 'solenoidal term' in the vorticity equation (the vorticity equation gives the rate of change of vorticity in time as a function of the phenomena being mentioned here: the divergence, the tilting/twisting term, the solenoidal term, friction): this means that within the plane of motion, lines of constant density are everywhere parallel to lines of constant pressure. Setting aside any changes in composition (generally rather small effect in the atmosphere), this also requires that lines of constant temperature (isotherms) are also parallel to the lines of constant pressure (isobars). One way to expand this in three dimensions is to have isothermic surfaces everywhere parallel to isobaric surfaces. Such a situation is called *barotropic*. There is no vertical geostrophic wind shear in a barotropic atmosphere. While the atmosphere is generally not barotropic, the adjective is sometimes applied to some processes occuring in the atmosphere - I think those processes which do not depend much on vertical wind shear or are not based on there being a vertical wind shear (??) - as opposed to baroclinic processes and things, which I think include synoptic-scale structures that tilt significantly with height (relative to horizontal wavelength?), and those processes depending on vertical wind shear and horizontal temperature variation. For example, I'm going to introduce Rossby waves by considering barotropic Rossby waves. One way to eliminate the solenoidal term in the equations of atmospheric motions is to use pressure instead of geometric height or geopotential height as a vertical coordinate. The solenoidal term simply dissappears. How can that be? Well, the vorticity of the wind field on an isobaric surface can be a little bit (but not generally much) different from that found on a flat horizontal surface because the pressure surfaces are not perfectly horizontal. The (vertical component of) vorticity in isobaric coordinates (x,y,p) is found by taking dv/dy - du/dx along the same p. Because pressure surfaces are generally nearly horizontal, it may be inferred that the solenoidal term of the (vertical component of) vorticity equation in (x,y,z) must not generally be very large. In a vertical plane, however, the solenoidal term is another way to describe what causes (in the absence of the coriolis effect) hot air to rise and cold air to sink. 5.*** So far I have been discussing vorticity of just the wind. If the wind is taken relative to the Earth, then this vorticity is actually relative vorticity. What is truly conserved if the conditions above (1-4) are met is absolute vorticity, which is the sum of relative vorticity and planetary vorticity. Planetary vorticity is the vorticity of the rotation of the underlying surface of the Earth. (The vertical component of) planetary vorticity is equal to the coriolis parameter f (the coriolis acceleration for a wind vector(u,v) is equal to (f*v , -f*u), and f is proportional to the sine of the latitude. The variation in f over a north south distance is equal to beta. Thus, beta is the meridional gradient of planetary vorticity, df/dy. So when the above conditions 1 - 4 are met, (the vertical component of) absolute vorticity is conserved following the motion (PS it is absolute vorticity that increases or decreases with convergence or divergence, respectively - as I had mentioned earlier in "It's volcanoes"... while discussing baroclinic instability and the growth of extratropical cyclones). This means that north-south movements require a change in relative vorticity in order to balance the opposite change in planetary vorticity. When divergence is nonzero, absolute vorticity is not conserved; but if the motion is adiabatic, isentropic potential vorticity (IPV, although just PV often means IPV and I will just use PV here) is conserved (at least of the other conditions 2 - 4 are met, and actually, I'm not sure but I think 3 and 4 dissappear in isentropic coordinates for adiabatic motion, leaving only 2 (friction). As (the vertical component of)vorticity in (x,y,p) coordinates is found by taking the variation of u and v over y and x within a constant p surface, isentropic PV is found by taking the variation of u and v over y and x within an isentropic surface (constant potential temperature); this gives the isentropic relative vorticity; this is then added to planetary vorticity to find the isentropic absolute vorticity, which is then divided by d(potential temperature)/dp (or something proportional to that) to find IPV. Thus, PV is higher where static stability is higher, all else being equal. absolute vorticity increases while conserving PV by vertical stretching (in isobaric coordinates) which corresponds to horizontal convergence due to the conservation of mass. -------- Most generally, Rossby waves can exist and propagate due to gradients in and the conservation (or near conservation over short-enough time periods) of PV, but to start, I'm going to consider barotropic Rossby waves in strictly barotropic two dimensional flow with assumed conservation of absolute vorticity.
130774. Patrick 027 at 10:48 AM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        So, setting irrotational components aside, what kind of wind field do I get? A point vortex, or a circular streamline with constant vorticity inclosed, result in (outside the circle) the concentric circular streamlines with wind speed inversely proportional to radius and proportional to the circulation of the point vortex or initial circle. In the case of a circle instead of a point vortex, within that central circle (containing finite vorticity of constant value at all points within) , there is pure orbital/curvature vorticity, and the velocity distribution is analogous to solid-body rotation, with wind speed proportional to radius Now what happens if I string out a line of point vortices, of equal strenght and spacing? I get a shear line. If the line is infinite, Wind blows parallel to the line and is in one direction on one side, the other direction on the opposite side, and constant speed everywhere. If I have an infinitely long rectangle instead, then the vorticity is finite within the rectangle and the wind speed changes gradually crossing from one side to the other, switching direction where it goes to zero. Within that rectangle, there is pure shear vorticity (provided the vorticity is uniformly distributed within the rectangle and the rectangle is infinitely long). IF the shear line (infinite vorticity distributed evenly along the line) or shear zone (rectangle) is not infinitely long, then (in the case of the rectangle, provided that it is relatively long compared to it's width) at sufficient distance from the endpoints and at sufficient proximity to the line or rectangle, the description in the previous two paragraphs still approximates the wind field. At sufficient distance from the line or rectangle, relative to length, the effect of elongation is reduced (it looks more and more like a point vortex or circle; the effects of small details (like variations in vorticity within the rectangle or circle or along the line) become less important relative to the effect of the total circulation of the central shape.). Notice the analogy to electromagnetism: The wind field about a point vortex is like the magnetic field around an infinitely thin wire with an electric current. The wind field around the circle is like the magnetic field around a wire of circular cross section with constant current density. The wind field around a shear line or rectangular shear zone is likewise analogous the the magnetic field produced by a current sheet. And the magnetic field at sufficient distance likewise is not so sensitive to the relatively small details (for example, if the wire had a square cross section). Similarly, the gravitational field at sufficient distance from a mass is not so sensitive to deviations from spherical symmetry of the mass. some deviations from a perfect dipole in the Earth's magnetic field also die out with distance (but others increase - those due to the solar wind, at least). Etc... Now with that background, we can move on to Rossby waves. (FINALLY!)
130775. Patrick 027 at 10:22 AM on 1 November 2008
        Arctic sea ice melt - natural or man-made?
        So at any distance from some unit area with some vorticity, there must be some circulation around it. The wind field is a vector field. This can be decomposed into component vector fields (this could be the two components parallel to the coordinate axes, but I am refering to components in a more general sense - suppose I have a vector field V = V(x,y) (V is a function of x and y). If I have two other vector fields V1 = V1(x,y) and V2 = V2(x,y), such that at each point (x,y), V = V1 + V2, then V1 and V2 form a complete set of components of V. And so on for three (or more) dimensions. It turns out that the vorticity of V is equal to the sum of the vorticities of each component V1 and V2 (at each point (x,y). The same is also true for the divergence of V, and also a number of other quantities that could be derived from either V or it's individual components. So, I could take V = Vir + Vnd. Vir is the irrotational component - its vorticity is zero everywhere. Vnd is the non-divergent component - its divergence is zero everywhere. There could be some component of V, Virnd, which is both irrotational and non-divergent, and so could be assigned to Vir or Vnd or divided up among them. Seperate components of Virnd potentially include a constant wind vector (invariant in x and y) and a pure deformation vector field, etc. Now suppose I take the total wind vector field, and find it's vorticity distribution. I then take out individual bits of vorticity times area (circulation) at each point (x,y), one at a time (of course for any realistic wind field, vorticity is finite and not concentrated into a finite number of zero-area points, so there will be an infinite number of circulation 'bits' and each is just infinitisimal in size). If I take out some small point vortex, I have to take out a wind field component with it, so that the circulation about that point at all distances no longer includes the effect of that bit of circulation associated with that point vortex. So I remove a component of the wind which has concentric circular streamlines centered at the point vortex, with speed inversely proportional to radius. If I do this until I am left with an irrotational wind field than I have found all components of the wind defined as those corresponding to units of vorticity times area, (bits of circulation). I can reconstruct the total wind field by adding all those components back. It is possible to reconstruct an entire wind field within some domain (in (x,y) space) based on it's vorticity field, provided some boundary conditions specified at the edges of the domain (to account for whatever irrotational wind field components there may be; notice that wind field components that are associated with vorticity only outside of the domain must be irrotational within the domain). PS1 this ability to reconstruct a wind field from it's vorticity is an example of 'invertability'. PS2 Actually, I'm not sure if this only strictly applies to the nondivergent wind field - does divergence need to be specified within the domain in order to account for divergent components of the wind? And again for three dimensions, etc... ------- A couple additional points on all that before moving on. 1. I've been describing two-dimensional flow on a flat surface. Which is a reasonable approximation for a small area of the Earth. If I am describing horizontal winds within a spherical surface, however, then any point vortex must imply an equal and opposite point vortex on the opposite side of the sphere (notice that both point vortices may be simultaneously cyclonic or anticyclonic, as the direction of cyclonic circulation is opposite on either side of the equator, etc...). The wind field is not inversely proportional to distance along the sphere at great distances - the wind speed much reach a minimum halfway to the opposite point and be neither increasing nor decreasing in either direction at that location. You might think that this would have profound implications for general circulation properties but it's not really a big deal (other complexities exist...) It doesn't mean that the southern hemisphere has to be identical to the northern hemisphere (even if the winds did not vary with height)... 2. On a flat plane, a point vortex accounts for a wind component defined as above that goes out to infinity. If it stopped at any point, there would have to be some opposite vorticity spread out along that outer circle. So one could say hypothetically that a point vortex must have some counteracting vorticity at 'infinitiy'. If space curves into a hypersphere then see last two paragraphs...
130776. chris at 08:56 AM on 1 November 2008
        Temp record is unreliable
        Re #36 that's good...you agree that the atmospheric CO2 levels vary only slightly due to effective atmospheric mixing. You say that this is "assumed", but of course, as we both know [http://www.skepticalscience.com/co2-measurements-uncertainty.htm], this isn't an "assumption" at all..it's a real world observation [so long as we are careful to make CO2 measures in isolated locations and average over the relevant timescales for mixing (yearly averages are appropriate)]. There's still a few problems with your post: (i) Temperature data isn't "used" for models of course. And so the "resultant" of the models isn't in any way "questionable" in relation to the temperature data which is an entirely independent data set. Model output (as predictions or hindcasts) might well be compared with the real world temperature....but that's another matter altogether. (ii) Notice that one doesn't need a huge number of "temperature recording stations" to assess changes in global temperature. Remember that the aim is not to determine the Earth's "average temperature" or "global temperature". These are terms with little meaning (after all the Earth's average sea level surface temperature will differ from the Earth's average 200 metres altitude temperature and so on). The Earth's temporal temperature evolution is determined as a change in the "temperature anomaly", which is the change in temperature in single locations averaged over a very large number of locations. Thus temperature stations at a whole range of locations and altitudes provide valid data sets. On similar lines, the fact that there is a strong correlation between temperature anomalies over large distances (100's of kilometres) means that the whole Earth doesn't need to be minutely sampled. Obviously we couldn't assess absolute global temperatures in this manner. But we're not assessing absolute global temperatures. We're assessing the change is absolute temperature at single locations and averaging these changes. So one needs to be clear about what the surface temperature anomaly means and how this is determined before attempting to trash it! [you might read the relevant descriptive papers here [*****]. Notice that in relation to the subject of this thread, the Earth's temperature anomaly progression under the influence of a marked 20th (and especially late-20th) century warming is essentially unchanged if the entire set of urban stations is omitted from the analysis. [e.g. Hansen et al (cited below) state in an analysis of urban heat effects that: “These examples illustrate that urban effects on temperature in specific cases can dominate over real climate trends. Fortunately, there are far more rural stations than urban stations, so it is not essential to employ the urban data in analysis of global temperature change.”] So the "urban heat island effect" is somewhat of a red herring (or a stalking horse) in the context of global temperature anomaly measures. [*****] Hansen et al (1999) GISS analysis of surface temperature changes J. Geophysical Res (Atmos) 104, 30997-31022 or (for the Hadley analyses): Rayner NA et al (2003) Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century J. Geophys. Res. (Atmos) 108 (D14): Art. No. 4407 JUL 17 2003 etc. etc. (iii) Of course the proof is in the pudding. We've observed a large warming, especially of the high Northern latitudes (as predicted by models) with large attenuation of Arctic sea ice....we've observed large scale retreat of mountain glaciers....we've observed increased concentrations of atmospheric water vapor in response to atmospheric warming much as predicted ......we've observed widespread increases in the sea surface temperature...and so on. In fact it's possible to leave out direct surface temperature measures and construct a completely independent temperature scale by analysis of the record of mountain glacier retreat: e.g. J. Oerlemans (2005) "Extracting a climate signal from 169 glacier records" Science 308, 675-677. And as John Cook outlined in his top post, there are many other indicators of rising surface temperatures that are independent of direct temperature measures.
130777. Mizimi at 05:42 AM on 1 November 2008
        Water vapor is the most powerful greenhouse gas
        Loss of heat from evaporation amounts to around 78 W/m or a quarter of the total insolation. The vapour rises into the upper troposphere and radiates heat into space. Wind driven circulation also pushes moist warm air into higher latitudes where the air is colder and drier; this warms the local atmosphere which then radiates heat into space at a greater rate as insolation is much lower. Yes, water vapour is a GG, but it also acts as a coolant within the hydrological cycle as a whole. http://eesc.columbia.edu/courses/ees/climate/lectures/o_atm.html http://www.env.leeds.ac.uk/envi2150/oldnotes/lecture3/lecture3.html
130778. chris at 01:04 AM on 1 November 2008
        What 1970s science said about global cooling
        Re #16 Not really Healthy Skeptic. "Denialism" is stupid when the thing you are denying is the evidence and its implications. After all it was pretty stupid to deny the evidence that smoking is a major causal factor in cancer and heart and respiratory disease. Many, many people paid for that stupidity with their health and lives (and continue to do so). It was pretty stupid to deny the evidence in the early 1980's that aspirin-taking was a causal factor in developing Reyes disease in children. Unfortunately many people were fooled by the stupid deniers of the time and suffered as a result. It was pretty stupid to deny the evidence that industrial chlorofluorocarbons result in catalytic destruction of high altitude ozone. Happily, in this case informed opinion and mature policymakers generally ignored the deniers, and so the latter didn't cause too many problems. Denialists don't deny "facts" of course. They deny the evidence by attempted misrepresentation. Some of the denialists of the phenomena in my previous paragraph are now denialists on behalf of those with agendas to mispreresent the science on global warming. So we'd be pretty stupid to take account of the obvious misrepresentations in the denialst nonsense of BTN's links in post #14! Happily, while there is a well-funded agenda of denialism on this topic (plus ca change!), there are now far many more mature and honest individuals with intact skeptical faculties who are able to see the "denialism" for what it is. The question is why some people are so stupid as to take obvious misrepresentations seriously. I wonder what they consider they are achieving in participating in this sort of chicanery? I have a horrible feeling that they consier that "believing" and propagating blatant untruths is a valid form of "politics"!
130779. chris at 00:42 AM on 1 November 2008
        What does CO2 lagging temperature mean?
        Re #29: Well yes, they were profoundly catastrophic effects Mizimi...and they occurred infreqently. And you might say that "in the scheme of things were relatively transient". However the present massive return of long-sequested carbon into the atmosphere by anthropogenic oxidation of fossil fuels is also: (i) infrequent (it hasn't happened at least for the last 20 million years) (ii) "relatively transient" "in the scheme of things". (ii) potentially catastrophic. One needs to be careful to make a proper assessment of events in the deep past, particularly in telescoping" these into "transient" phenomena, when in many cases they certainly weren't. For example the Jurassic extinction (see Svensen et al, 2007, abstract in my post # 28), was likely the result of release of greenhouse gases over many 1000's of years to buils up atmospheric concentrations to catastrophic proportions. Likewise the extinctions associated with the opening up of the N Atlantic plate boundary at the Paleo-Eocene Thermal maximum (PETM) were probably due to a rather long-lived explusion of greenhouse gases into the atmosphere. In fact (see Keller, 2005; abstract in my post #28) there isn't much evidence for impacts in extinctions outside of the end Cretaceous extinction. From the perspective of some time point in the deep future, a period of 2-300 years of pumping CO2 into the atmosphere at the rate of 2-4 ppm per year will look like an extremely "transient" event. And notice that in the general case (see Mayhew et al. 2007; abstract in my post #28), low biodiversity in the fossil record is associated with warm periods. So it doesn't take "transient" catastrophies to warm the world to the extent of greatly reducing biodiversity In other words, jut because human perception makes processes occurring within our lifetimes on the decadal/centennial time scale seem extremely slow (and seemingly innocuous), they are not necessarily any less "transient" or possibly less catastrophic, then events in the deep past. In fact the rate of enhancement of atmospheric greenhouse gases now is likely far higher than during many of the tectonic phenomena leading to massive extinctions in the deep past. Of course where we have an advantage now, is that we know what is going on and are in a position to do something about it. We'd be extremly stupid to let events get too far out of control...
130780. Patrick 027 at 15:25 PM on 31 October 2008
        Arctic sea ice melt - natural or man-made?
        Vorticity: Clarifications: 1. the derivation of vorticity from the wind field, as described above, is based on the wind at an instant in time. Streamlines are also based on the wind at an instant in time; streamlines are everywhere parallel to the wind velocity, and the wind speed is inversely proportional to the spacing of streamlines in two-dimensional flow** (**for non-divergent winds: divergence = du/dx + dv/dy, non-diverence wind implies du/dx + dv/dy = 0; a two dimensional wind field can always be decomposed into an irrotational portion with zero vorticity, and a non-divergent portion which must have any vorticity that exists in the total wind; streamlines, which are contours of the streamfunction, can be defined for the non-divergent component of the wind.) So for example, pure orbital/curvature vorticity corresponds to streamlines that, in the direction locally perpendicular to themselves, are equally-spaced. The streamlines curve; if the vorticity is constant, the streamlines must form arcs that are parts of concentric circles ... No, wait, is there another way to do that? Can constant orbital vorticity correspond to something other than solid body rotation? For a moment I had an idea***... have to think about that - anyway, it's not important for the rest of this. For pure shear vorticity, the streamlines are straight; they're spacing varies along a direction locally perpendicular to themselves. This is at an instant in time, so if the streamlines are changing in time, the motion of the air parcels can vary - they could have trajectories that are straight even where streamlines curve and vice versa, or the curvature could be in the opposite direction. So I was inaccurate when I wrote "Where there is only shear vorticity, the wind is not changing direction." Pure shear vorticity, an absence of curvature vorticity, requires the wind is not changing direction along a streamline at an instant in time, which is a relationship among different air parcels. It is not required for each individual air parcel to not be changing its own direction of motion. 2. I have been so far discussing vorticity as a scalar quantity. It can be treated as such for flow in two dimensions. In general, though, vorticity is a vector. The component of that vector which I've been focussed on is that which is perpendicular to the two dimensions of the flow I've been describing; for horizontal flow, it is the vertical component. If the horizontal flow varies with height, it can/will have horizontal components of vorticity as well, but for introductory purposes, assume the flow is identical at each level so that the only component of vorticity is the vertical component (in the z direction for x,y,z coordinates). --------- So I left off describing an irrotational (zero-vorticity) wind field of concentric circle streamlines centered on some region which contains voriticity. Now for Stoke's theorem: Take an enclosed area. Take the wind velocity at all points along the perimeter of that area. At each point, take the component of velocity that is parallel to the perimeter at that same point. If that component points such that continuing in that direction is counterclockwise around the area, count it as positive, otherwise count it as negative. Now integrate this value along the length of the closed perimeter, stopping where you started (a complete revolution). This is the **circulation** around the enclosed area (it has units of wind speed times length, such as square meters per second). (obviously a somewhat different usage of the word than in the context of 'general circulation of the atmosphere or ocean' or 'the fluid is circulating'...) It turns out that the circulation around such a closed path is equal to the area-integrated vorticity contained within it (this can be proven mathematically). Or in other words, the circulation around an area, divided by that area, equals the area average of vorticity in that area. In three dimensions, that area is on a surface. That surface can be any surface whose edge is on the same path (so if the path is in a single plane, the surface need not be on that plane - it could be a curved surface). In this more general case, it is the component of vorticity locally perpendicular to the surface that must be integrated over the area of the surface to find the circulation, or be averaged over that area to get the circulation be unit area. (PS in general, the vorticity as a vector is equal to the 'curl of the wind vector' which is written mathematically as the gradient operator *cross* the wind vector (somewhat like a vector cross product, except the first 'vector' is an operator; the divergence is written like a vector dot product with the wind vector, but again with that operator as the first 'vector').) Now back to two-dimensional flow. Consider the wind field where the streamlines form concentric circles around a center point, and starting at a distance R from the center, the wind is inversely proportional to the distance from the center. Since the circumference is proportional to the distance from the center (the radius of the circular streamline), the product of the wind speed and the circumference of the streamline it is on is constant over a range of distances. Since the wind velocity is parallel to the streamlines, this means the circulation around each streamline is the same. Which means that the circulation of two different concentric streamlines are the same, which thus means the circulation around the area of an annulus between two such streamlines is zero (the circulation around an area with a hole in it is equal to the circulation oround the outer boundary minus the circulation around the inner boundary, in other words, it is the circulation of the larger area included the hole, minus the circulation of the hole). This means the average vorticity within the annulus is zero. This is true except within the circle of radius R at the center of this structure. Notice that maintaining the same wind field outside of that central circle which must contain all the vorticity, I can redifine the wind field between radius R and radius R2 from the center to again be inversely proportional to the radius, with the same wind speed at R, and then all the vorticity is concentrated into a smaller circle of radius R2. The circulation around this smaller circle must be the same as that around the larger circle. Thus the wind field outside this central circle doesn't depend on the size of the cirle, only on the circulation of the circle and thus the area-integral of vorticity within it. A point vortex can be defined, which has infinite vorticity at a single point, but only some finite circulation, and this would correspond to a wind field with concentric circular streamlines, with wind speed inversely proportional to radius, and the wind speed at a reference radius R0 being proportional to the circulation 'possessed' by the point vortex. Will have to continue later; but what is coming is an illustration that the wind field can be reconstructed by it's vorticity distribution. (At the same instant in time, anyway, although under some conditions vorticity is conserved following the motion, so that ... etc.)
130781. Patrick 027 at 13:01 PM on 31 October 2008
        Arctic sea ice melt - natural or man-made?
        "This is getting interesting." Great! "Where are you getting this information from?" physics, math, college courses, and textbooks, the last including: "Introduction to Dynamic Meteorology - Third Edition" by James R. Holton "Introduction to Geophysical Fluid Dynamics" by Benoit Cushman-Roisin If you wanted to get these, of course you'd want the most recent editions; the third edition of Holton does have an error in Chapter 8 in section 8.2.1 (for a while I couldn't figure out how the math was being done and then I figured out why! But I think the ultimate conclusions may be correct anyway (perhaps the math was originally done correctly and then a few steps were copied wrongly)). As for Cushman-Roisin - a great dynamics book, but be aware the brief description of global warming is not good. -------------- Before going on, a few clarifications: 1. the constant basic-state density with height approximation: The description of gravity waves I had in mind was derived mathematically from equations using a constant-density approximation. In at least some ways this can be a good approximation because and so long as the individual air parcels themselves do not rise or fall so much with height, but obviously a vertically-propagating or perhaps even an evanescent wave will propagate through a greater depth of the atmosphere, and of course the atmospheric pressure and density decrease to a first approximation exponentially with height. Again, I haven't gone through the math entirely for myself, but from Ch 12 of Holton, it seems there's a general tendency, if not exactly than approximately, for vertically-propagating waves of various kinds - (including planetary (kind of Rossby) waves, equatorial Kelvin waves, equatorial Rossby-gravity and gravity waves and (are there vertically-propating equatorial waves that are purely Rossby?)) - to increase amplitude in proportion to the square root of the inverse of density (the inverse of density also known as specific volume (volume per unit mass)). However, I don't think this means the energy or momentum flux is increasing with height, at least not just from that alone. 2. Just to be completely clear, I was refering to the group velocity and phase velocity earlier relative to the flow of air. Thus they generally have horizontal components even if the waves are stationary relative to the surface; the wind moves through the waves, hence the waves move through the air. (ps for waves in one dimension, phase velocity = frequency times wavelength: c = f*l group velocity = change in frequency per unit change in wavelength: cg = df/dl the angular frequency w = 2*pi*f, and the wave number k = 2*pi/l, so: c = w/k cg = dw/dk In multiple dimensions, c and cg can be vectors and k can also be a vector (the wave number vector, or I think it's okay just to say wave vector). In this case, cg = the gradient of w in k-space (which means, the x component of cg is equal to the rate of change of w per unit change in the x-component of k. Note that the gradient may vary over k-space, which makes cg a function of the k vector). One has to be careful using c (phase velocity - I'm going to use that term here though I'm not 100% sure if that's technically the correct term) as a vector (which is to be perpendicular to planes or lines of constant phase (troughs, crests, etc.)- the different components of c are not equal to the phase speeds in those different dimensions. The reason for this: imagine a diagonal line on the x-y plane moving perpendicular to itself at speed c. The phase speed in the x-direction, cx, is the speed of the x-intercept. If the line is nearly parallel to x, cx can approach infinity for a finite value of c. However, the inverses of c, cx, and cy add like vectors - as if 1/cx and 1/cy were the vector components of 1/c. Note that the cx (the phase speed in the x-direction) = w/(x-component of k). (see appendix A of Cushman-Roisin, "Wave Kinematics") Without going into the precise mathematical derivation based on the relationship between group velocity and other wave properties for vertically propagating gravity waves, it can be seen from the geometry that the horizontal phase speed (the inverse of the horizontal component of the vector in the phase velocity direction with magnitude 1/c) must be equal to the horizontal component of the group velocity (I think the horizontal and vertical components of group velocity do actually add as vectors - No, wait...????????) ... well, what I was going to say was that if the wind speed slows down with height, then (if I am correct here**) the group velocity not only becomes closer to horizontal (as the phase velocity is increasely farther from horizontal), the vertical component must become smaller, which means the propagation of energy and momentum slows down. This would then explain more clearly why, per unit vertical distance, all else being equal, wave damping would increase, so that the wave would dissipate faster per unit distance, so that per unit volume, the momentum and energy transferred from the wave to the background (basic or mean) state would increase. One has to divide by density to get the effect per unit mass, of course (momentum = velocity times mass). *NOTE* that this happens where the frequency of the wave relative to the air is reduced - where the wind velocity relative to the horizontal velocity of phase propagation is reduced (I stated that more generally because some waves may not be stationary relative to the surface, depending on what causes them, changes in the wind, etc.). PS the geometrical relationship between phase plane orientation, group velocity and phase velocity - what is parallel or perpendicular to what - is common to more than just vertically-propagating gravity waves. It applies to some other kinds of vertically-propagating waves, including equatorial Kelvin and Rossby-gravity waves. In the case that the wind relative to the horizontal position of the waves goes to zero, the group velocity, as I understand it, must go to zero. This means there is a convergence of wave energy and momentum - if the group velocity is still upward at some level beneath this critical level. Even if the waves have reached a steady state beneath this level, wave energy and momentum must continuously accumulate at such a critical level. This would explain the quote from Holton earlier: " Holton p.284: "Amplitude enhancement leading to wave breaking and turbulent mixing can occur if there is a 'critical level' where the mean flow goes to zero," - 'critical level' in the original is italicized instead of in single quotes " I would expect that this is another way that the momentum of the wave is transferred to the air at that level as opposed to just propagating through it and moving on. 3. Pressure perturbations and temperature perturbations: What allows gravity waves to exist is that, within a stably-stratified fluid (lapse rate less than the adiabatic lapse rate, so that potential temperature increases with height (or potential density decreases with height, where potential density is the density the material would have if brought adiabatically to some reference pressure) is that when air is displaced vertically so that the pressure changes, the temperature changes more than the temperature of the surrounding air, so that lifted air is more dense and will tend to sink, and air pushed down will be less dense than surrounding air at its new level and will tend to rise. The vertical accelerations do require pressure perturbations that are not in hydrostatic equilibrium (in other words, there must be some small imbalance between gravitational force and the vertical pressure gradient force). However, there are also pressure perturbations that are in hydrostatic equilibrium with the temperature perturbations. The temperature perturbations are in part due to the pressure perturbations but also to the vertical displacements that cause changes in pressure following the air as it moves. Thus, if we designate the vertical maxima in trajectories as crests and the vertical minima as troughs, the troughs tend to be warm and the crests tend to be cold. This means that, relative to the background (basic) state, the 'hydostatic pressure' decreases more with height through crests and less with height through troughs. When the phases are tilted, the hydrostatically-balanced portions of the pressure perturbations are thus high pressure under crests and above troughs and low pressure above crests and beneath troughs, with pressure extremes 90 degrees (1/4 wavelength) out of phase with the vertical displacements. These pressure perturbations push the actual temperature perturbations a little higher than otherwise, which in turn pushes the pressure perturbations a little higher than otherwise, but probably not much for small-amplitude waves. On the other hand, non-tilting phases require that the hydrostatically-balanced portion of the pressure perturbation is high pressure in the crests and low pressure in the troughs, and decreasing with height even for constant vertical displacement amplitude; but of coures the amplitude decreases with height, and it works out if both decrease exponentially with height (at least before taking into account the density variation with height of the basic (background) state, but I think the picture is still qualitatively similar). In this case, the temperature perturbations are reduced from what they would be because the pressure perturbations are opposite the pressure variations following the air motion. As long as the amplitude is small enough, however, everything should be the same sign as so far described (I think. It's possible to imagine the opposite scenario... well I'd have to think about that - I haven't done the math yet**). The non-hydrostatic portion of the pressure perturbation is necessary to balance the vertical accelerations. It will thus be high pressure beneath troughs and low pressure above troughs, to accelerate the air upward from the troughs. And the opposite for crests, where the air's upward motion slows and reverses: a downward acceleration. Notice that for tilted (vertically-propagating) waves, this is 180 deg (1/2 wavelength) out of phase of the hydrostatically-balanced pressure perturbation (before the readjustment to the adjustement to temperature). There is also horizontal acceleration because, subtracting the basic state wind from the total, the waves involve cycling slantwise motion parallel to crests and troughs. So... Now I have to do more to figure it out, but the diagram on p.202 of Holton shows high pressure over the trough and under the crest, with cold near or at the crest and warm near or at the trough, and the pressure and temperature perturbations 90 degrees (1/4 wavelength) out-of phase. As for the evanescent waves, ... I need to figure more about before going farther with that...** 4. Form drag and layers of air: It is important when considering momentum transfer by form drag to define layers of air by material surfaces (or in cross section, material lines). A material surface is either parallel to motion or moves with the air; trajectories never cross material surfaces. Streamlines can cross material surfaces so long as the material surfaces move along them. In the case of the layers of air considered here, the material surfaces are displaced vertically along with the air as it moves, so a layer of air is ridged. For vertically propagating waves, the pressure perturbations are such that, on the upper material surface, there are higher pressures on one set of slopes and lower pressures on the other set, so that there is a net force acting on the air layer in the horizontal. However, if the amplitudes of both the the 'pressure wave' and the vertical displacements are the same at the bottom of the layer, then the forces acting from below on the bottom material surface exactly oppose that from above. The difference in forces acting on the bottom and top of material surfaces that would be due to variation in the wave 'strength' with height would result in a net sideways force on the layer of air. If this is not the case with amplification with height of the wave displacements due just to decreasing basic-state density, then that could be because the pressure perturbations simultaneously decrease with height (due just to the density decreasing with height, again) in sufficient proportion (?). This concept of form drag based on forces on material lines is also useful with vertically-propagating equatorial Kelvin and Rossby-gravity waves (among others, I'd think). So there are a few things there I'm not sure about but overall I think/hope that still helps. Now back to vorticity and Rossby waves... to be continued...
130782. chris at 09:11 AM on 31 October 2008
        Human CO2 is a tiny % of CO2 emissions
        "More or less in balance" isn't "a cop out". There's a pretty good understanding of the short term and medium term carbon cycle that dominates the carbon flux between the atmosphere and biosphere, and on longer periods, the atmosphere and terrestrial environment. So to answer your first question: ["How much out of balance does it have to be before you consider it not in equilibrium?"] If atmospheric CO2 levels haven't varied much more than about 20 ppm (maybe 30 ppm according to some plant stomatal index analyses) around 280 ppm for the last 10,000 years before the 20th century, one can conclude that the system has been more or less in balance. It's not "a cop out" to state the obvious. The flux of carbon into the atmosphere has been reasonably closely balanced by the flux out of the atmosphere for vast periods of time before the 20th century. And if one considers the 10 million years before the 20th century, the atmospheric CO2 seems to have been pretty much near equilibrium. So if one considers only the interglacial periods, the atmospheric CO2 was below or around 300 ppm during this entire period according to the proxy record: e.g. Pearson, PN and Palmer, MR (2000) "Atmospheric carbon dioxide concentrations over the past 60 million years" Nature 406, 695-699. M. Pagani et al. (2005) "Marked Decline in Atmospheric Carbon Dioxide Concentrations During the Paleogene", Science 309, 600 – 603. T. K. Lowenstein and R. V. Demicco (2006) "Elevated Eocene Atmospheric CO2 and Its Subsequent Decline" Science 313, 1928. R. M. DeConto et al (2008) "Thresholds for Cenozoic bipolar glaciation" Nature 455, 652-656 Note that it's worth distinguishing the interglacial and glacial periods here, since the shift of atmospheric CO2 down to around 170-180 ppm during glacials is similarly part of the short term carbon cycle that relates to the distribution of carbon between the terrestrial biosphere, oceans and atmosphere. In this case it's the temperature-dependent element of the cycle and its response to very slow insolation variation (Milankovitch cycles). So we can talk about being "near equilibrium" or "more or less in balance" in quite explicit terms: (i) On the timescale of 1000-10,000 years, the relatively fixed amount of ACCESSIBLE carbon distributing between the atmosphere, oceans and biosphere has maintained an atmospheric CO2 concentration that has undergone relatively little variation (the overall variations during 1000's of years of the order of the changes now occurring in about a decade). (ii) on the timescale of 10 million years the longer term carbon cycle involving the sedimentation of carbon as carbonates in the deep oceans and the slow release of carbon from ocean plate subduction and volcanic activity has also been more or less in balance. The atmospheric CO2 record of the last 10 million years suppoorts that conclusion. (iii) On top of the equilibrium carbon distributions of the carbon cycle on the millions of years timescale, insolation variations (Milankovitch cycles) cause very slow requilibration of CO2 between the atmosphere and ocean/terrestrial environments. Now something quite different is happening. A massive store of excess carbon inaccessible to the carbon cycle for many 10's of millions of years is being rapidly reintroduced into the system in an extraordinarily short time period. Not surprisingly the atmospheric CO2 concentration is rising very rapidly indeed. The atmospheric CO2 concentration is out of equilibrium (there's a large nett flux into the atmosphere from previously long-sequestered sources), and the atmospheric CO2 concentration is being driven up towards some new equilibrium concentration. And the above also address your second question: ["How does all that CO2 locked up as carbonate sediment compare to the oil/gas/coal deposits?"] That's not quite a relevant question. Considering carbonate sediments and their formation, the long term paleoCO2 record of the last 10 million years or so indicates that carbonate sedimentation has been pretty much in balance with the return of CO2 from subducted carbonate back through volcanoes into the atmosphere. ...where the "out of balance" element has arisen is the awesomely rapid oxidation and return to the atmosphere of massive stores of carbon previously sequestered out of the short and medium carbon cycles for 10's and 100's of millions of years. Note that dynamic systems CAN be in equilibrium. In general they fluctuate around equilibrium states. Of course one can raise semantic issues about the extent to which a particular fluctuation constitutes a departure from equilibrium. But it's quite easy to be explicit and define exactly what one means by the particular equilibrium in question.
130783. chris at 08:13 AM on 31 October 2008
        It's Urban Heat Island effect
        O.K. so you agree that the colours denoting changes in temperature are entirely appropriate in the light of the completely general use of the colours asssociated with the visible part of the EM spectrum to denote temperature and temperature change (e.g. in thermal imaging of body temperature as in my link in post 5). That's good. But you're going to carry on maintaining that there's some sort of a disconnect between the satellite photo of the Earth at night (which is a pretty good identifier of urbanization and its density) and the surface temperature anomaly. It should be obvious that if one were to take the satellite picture of the Earth each night and average this for a year, that it would look pretty much the same as the snapshot. Or do you consider that averaged over a whole year there would magically appear lights from massive connurbations in the Arctic and Alaska, the vast Northern territories of Canada and Serbia, the empty regions of Australia, North and Central Africa and so on...? ...I think not.
130784. Mizimi at 06:44 AM on 31 October 2008
        It's Urban Heat Island effect
        Chris: thermal imaging does not produce colours..these are added by the software interpreting the input data as selected by the user. I accept we 'naturally' take white/orange/red to be 'hot' and blue/green to be 'cold' but how cool is a methane flame? Our bodies detect IR quite well but not UV, yet more people get sunburnt than fireburnt. My point about the two images above is that the temp anomaly is a compilation of a years data and thus the UHI's would be obscured. We regularly fly thermal imaging 'sorties' over our airfields to assess which buildings are inadequately insulated ( as well as to give the pilots some practise), but we do it at night to improve the image contrast. UHI effect will also vary according to season. So if these images are supposed to show that UHI effect is so minimal that they do not affect global temp, then, in my opinion, they fail.
130785. Mizimi at 05:46 AM on 31 October 2008
        It hasn't warmed since 1998
        PS: that should be 2108 of course!!
130786. Mizimi at 05:28 AM on 31 October 2008
        It's the sun
        QM: Yes, the plastic is modified polythene which is translucent. Part of the effect is due to albedo (colour) and part due to low incident angle reflection (shiny surface). Both effects diminish with age, (darkening of the colour and accumulation of dust) but the plastic only lasts about 3 years and then is replaced. Much of the plastic is recycled ( even the plastic string used for baling and tying plants!!) and turned into garden and playground equipment. Some is even re-inforced with steel bar and used as I beams for lightweight construction. True greenhouses hold temps up because they minimise losses thro' convection/windage rather than trapping heat by preventing re-transmission of IR ( although you can buy IR glass which acts just like a GG...a bit expensive tho'). Translucent fibreglass will do the same but I do not know the light transmission characteristics of this material...you might end up cutting the light frequencies the plants need. Why tempered glass? Ordinary 2 or 3mm plain window glass is perfectly OK and the cheapest. Don't forget to have vents to control the temp in summer....you don't want to cook the plants!
130787. Quietman at 16:49 PM on 30 October 2008
        Arctic sea ice melt - natural or man-made?
        Patrick This is getting interesting. Where are you getting this information from?
130788. Quietman at 16:44 PM on 30 October 2008
        It's the sun
        Mizimi That is interesting. I am planning to build a greenhouse to counteract the cooling conditions here. Is the increased albedo because of the plastic? I was planning on using tempered glass and translucent fibreglass.
130789. Patrick 027 at 15:04 PM on 30 October 2008
        Arctic sea ice melt - natural or man-made?
        Rossby waves: First, notes on vorticity. Vorticity = dv/dx - du/dy ; that is, the variation in the meridional wind component (v = Dy/Dt) going from west to east, MINUS the variation in the zonal wind component (u = Dx/Dt) going from south to north. Or in any coordinates (s,n) where facing in the direction of positive n, s points to the left, then the vorticity is the rate of change in the n direction of the s-component of velocity over n MINUS the rate of change in the s direction of the n-component of velocity; voriticity = d(Dn/Dt)/ds - d(Ds/Dt)/dn. (where Dq/Dt for any q is the velocity in the q direction; D/Dt is the langrangian or material derivative, which means it is the time derivative following the motion of the air; hence Dq/Dt is the rate of change of location along q following the air's motion.) Vorticity is the sum of two components: shear vorticity, and orbital or curvature vorticity. If there were only orbital/curvature vorticity, then the motion is simply rotation about a point. At each point at which this is the case, du/dx = - dv/dy, and d(Dn/Dt)/ds = - d(Ds/Dt)/dn, for any orientation of (s,n) axes. Over the space in which the vorticity is constant, the air would be rotating as if parts of the same rigid object, and there would be no deformation (if the air were tagged with shapes, the shapes would be rotated but remain the same size and shape). If only shear vorticity is present, then for a given location it will be possible to find some orientation of (s,n) such that one of d(Dn/Dt)/ds or d(Ds/Dt)/dn is zero. Suppose it is the first which is zero; in that case vorticity = shear vorticity = d(Ds/Dt)/dn. Where there is only shear vorticity, the wind is not changing direction. It is possible to have shear vorticity and orbital/curvature vorticity of opposite signs, in which case, if of equal magnitude, the total vorticity would be zero. One such case would be a wind field in which the streamlines form concentric circles, but outside of the central point or a central circle, the wind speed is inversely proportional to the distance from the center. Within the central circle, there would have to be some vorticity, or if there is only vorticity at the central point, that would have to be infinite vorticity (but just at one point, so that the vorticity integrated over area (for now, call that C) would be finite). To be continued...
130790. Patrick 027 at 11:22 AM on 30 October 2008
        Arctic sea ice melt - natural or man-made?
        ... well, now I'm not quite sure about the lack of form drag (the phase of pressure relative to displacement) with non-vertically propagating gravity waves, but anyway, moving on: If the forcing is at lower frequency than the buoyancy frequency, then: Vertical propagation occurs. surfaces of constant phase (crests and troughs) tilt with height. An interesting thing about these kinds of waves is that the group velocity is at right angles to the wave vector (which is perpendicular to the crests and troughs). The wave vector is in the direction of phase propagation. The group velocity is parallel to the crests and troughs. Relative to the air, for gravity waves emanating from the surface (such as from wind blowing over ridges), the crests and troughs move downward at an angle but build upward (along themselves) at an angle (at the group velocity), so that in steady state conditions, the wind blows through a stationary tilted crest and wave pattern. The pressure perturbation and vertical displacements are positioned so that there is form drag - there is higher pressure on the windward sides of the ridges and lower pressure on the lee sides. Thus there is a net force on the ridges, which means the air is losing momentum to the ridges. However, as each layer of air loses momentum to the layer below by the same process, it gains momentum from the layer above. If the gravity wave propagates upward without dissipation, there is no net loss of momentum. Ultimately the momentum transfered to the solid Earth from the air by the form drag is then taken from the air at levels where the gravity wave is dissipating (or otherwise ceasing to propagate as just described?). When the winds vary in time, the formation of gravity waves will change and I expect those changes to propagate at the group velocity. The winds and static stability can and will change with height, which will affect gravity wave propagation. Where the wind is slower, the frequency of the waves is reduced relative to the air following its motion - my understanding is that this (perhaps just because of the period of motion, or perhaps also because the tilts change so the group velocity goes farther away from the vertical?) allows for enhanced thermal and mechanical damping of the wave at such levels (per unit volume ?). Mecahnical damping would be by viscosity - including eddy-viscosity (the eddies in this case would be on smaller scales); concievably it might include something else**??. Thermal damping can occur because there are pressure perturbations in a gravity wave, which cause small adiabatic temperature variations, which then cause small variations in radiative (photons) cooling rates, which is not an adiabatic process and will reduce the gravity wave amplitude. In such gravity waves, the perturbation velocity and motion is parallel to the constant phase surfaces (crests and troughs, etc.) and oriented so that the horizontal projection is parallel to the mean wind. Inertio-gravity waves are gravity waves in which the fluid parcel oscillations are slow enough (slow wind, very very very broad ridges, low static stability) for the coriolis effect to become significant - so that the perturbation trajectories form ellipses rather than a line segment (following the air with the mean wind). As this happens, the coriolis effect becomes part of the restoring force. I haven't gone thoroughly through the math but from what I've read ("Introduction to Dynamic Meteorology - Third Edition" by James R. Holton - see chapters 7 and 9 in particular for gravity waves) vertically propagating inertio-gravity waves must have frequencies (following the motion of air parcels) between the buoyancy frequency (generally much much more rapid, and in that limit, crests and troughs approaching vertical) and the inertial oscillation frequency (proportional to the coriolis effect, and in that limit, crests and troughs approaching horizontal). I'm not sure what happens when the frequency is less than the inertial oscillation frequency - I suppose in that case the wave can't propagate. That might be why, in the context of inertial oscillations in the ocean excited by the wind, I've read that these can not propagate toward higher latitudes (but I was skimming that material, so don't take my word for it). Typically ridges don't have the profile of an endless sinusoidal wave with constant wavelength. Wind blowing over irregular topograph, or a single ridge, may excite a spectrum of gravity waves; depending on conditions, some may propagate vertically and some others may decay with height exponentially. (Of course, at high amplitudes, nonlinear effects, such as wave-wave interaction, may become a bigger factor). Sometimes conditions may allow vertical propagation but only up to some level, at which point the waves don't propagate further. I expect there'd be evanescent waves above that level (because the amplitude can't discontinuosly jump to zero - the same condition that requires evanescent electromagnetic waves beneath a reflecting surface). The gravity waves may reflect from that level. Repeated reflection between the surface and the upper level can generate trapped lee waves (Holton, p.284). Reflection may play some role in downslope windstorms but nonlinear processes are important in that phenomenon (Holton, p.284-285; also try looking up 'Froude number', 'hydraulic jump'). Without going into all details, Holton p.284: "Amplitude enhancement leading to wave breaking and turbulent mixing can occur if there is a 'critical level' where the mean flow goes to zero," - 'critical level' in the original is italicized instead of in single quotes (see also 'Scorer parameter'). Gravity waves with downward group velocity may occur presumably upon reflection from above - perhaps they could also occur from wind blowing underneath and relative to a disturbance in the air, though I haven't read of anything like that. Gravity waves can be excited by wind blowing over cumulus convection, and also may be produced by that convection itself (in that case, gravity waves may radiate away from the disturbances). 2. Rossby waves (to be continued)...
130791. Patrick 027 at 05:35 AM on 30 October 2008
        Arctic sea ice melt - natural or man-made?
        "Try to remember my background is engineering not climatology or theoretical physics. " I have a little bit of engineering and basic physics background but I'm not sure exactly what you mean about eddy currents in electricity. However, I really haven't begun to explain how these mechanical waves propagate. So to correct that, here are two important examples: 1. Gravity waves exited by wind blowing over sinusoidal ridges. Take the (arbitrarily-defined) layer of air closest to the surface. Without wave-breaking, the air moves up and down over ridges. It thus has to accelerate. So there will be pressure variations. Take the next layer of air - because the first layer is displaced, the next layer must be displaced, etc. As a function of the wavelength of the ridges and the wind speed, there must be some frequency of oscillation for the air as it blows through this set-up. If the air is stable (potential temperature increasing with height), air displaced vertically will tend to fall back to where it was, and oscillate about an equilibrium level - in the absence of forcing, this continues except for thermal (radiative - photons) and mechanical dissipation of the potential and kinetic energy involved. This natural frequency is called the buoyancy frequency or Brunt-Vaisalla (sp?) frequency. If the forcing of gravity waves is at a higher frequency, (unless I have this backwards), then the gravity waves produced by wind blowing over ridges decrease exponentially with height; there is no vertical propagation of the energy. There is no form drag - that is, the pressure perturbations associated with the gravity waves are aligned with vertical displacement maxima and minima so that there is no sideways forcing. The dissipation that would occur is by viscosity, which would occur in the absence of gravity waves (wind blowing across the surface tends to lose momentum to the surface (and hence the Earth), and wind at different levels at different speeds can exchange momentum via viscosity, though that is not generally a dominant factor in atmospheric motions away from the surface). On the other hand, if the forcing frequency (determined by the wind and the wavelength of the ridges) is less, than ... to be continued...
130792. Quietman at 16:16 PM on 29 October 2008
        Arctic sea ice melt - natural or man-made?
        Patrick So you are saying that eddy waves are similar to eddy currents in electricity rather than in aerodynamics? Try to remember my background is engineering not climatology or theoretical physics.
130793. Patrick 027 at 14:57 PM on 29 October 2008
        Arctic sea ice melt - natural or man-made?
        ... I think that - either when there is zero EP-flux or when the EP-flux divergence is zero?, then the wave is not dissipating (or amplifying or breaking) and so is not altering the mean state (it must be the first, because even without EP flux divergence, there is some alteration - but maybe it has to be reversed in time?). In such a case a wave can propagate by making only temporary changes (as electromagnetic waves may nudge the matter in a transparent material along the way (which affects how the wave propagates).
130794. Patrick 027 at 12:43 PM on 29 October 2008
        Arctic sea ice melt - natural or man-made?
        "Re: 276 I am just guessing but doesn't direct nonstop sunlight on the poles during a 6 month long day have a little to do with this?" YES! (And that will bear on any changes in solar forcing, but in and of itself is just part of the regular seasonal cycle which changes on timescales of several thousand years and longer...) "Re: 277 I have no clue as to what that means. Are you talking about wind or radiation? Eddys are circular currents caused by turbulence (in water or air) so I do not follow. " Not about electromagnetic radiation as in photons. These are mechanical waves. Waves are often thought of as sinusoidal in some way, but one can have a single wave pulse. There's phase velocity and group velocity - for dispersive waves, not the same thing. (Energy propagates witht the group velocity.) In order for waves to occur there must be a restoring force - gravity, pressure, elasticity, etc... In the context of geophysical fluid dynamics, I'm not sure exactly if there is a distinction between eddies and waves. Eddies can propogate. Rossby waves involve rotation. Cyclones that develope in midlatitudes are an aspect of baroclinic waves, which I think may be considered a kind of Rossby wave... It is true that in order for baroclinic instability to occur, there must be some vertical level, called a critical level (or steering level in this case, for obvious reasons) where the wind averaged across the baroclinic wave (a basic state wind) is equal to the velocity of the motion of the baroclinic wave (at least in the case where the average wind is not changing direction with height); however, above and below, the wave is propagating through the air. Even if we ignore vertical motion, the air at the center of a cyclone is not necessarily going to be at the center of the same cyclone in the near future; Even if a cyclonic circulation is strictly two-dimensional and axisymmetric, so that at any instant the streamlines (parallel to the wind vector at each location) are circles, propagation of this streamline pattern can be such that individual trajectories spiral into and out of the cyclone and in some cases may curve anticyclonically. ... Often an analysis of the atmosphere is made using zonal averages - these are averages over all longitudes - so that they might be graphed in two dimensions (if averaged over some specific time period or at some particular moment in time, etc.). Then there are zonal means, mean temperature, zonal (westerly) wind, and the mean meridional circulation (north-south and up-down). Motions that average to zero are attributed to eddies. Correlations of some parts of eddies with other parts of eddies can yield nonzero eddy fluxes - for example, in this perspective, the average eddy temperature deviation is zero, the average eddy meridional wind velocity is zero, but the average of the product of the two can be nonzero - thus there is a nonzero northward temperature flux by eddies. The average zonal velocity of eddies can also be zero, but a correlation between eddy zonal wind velocity and eddy meridional wind velocity can yield a nonzero northward eddy flux of zonal (westerly) momentum. The average of the square of the eddy wind speed will be nonzero, and hence so will the eddy kinetic energy. One way of analyzing how eddies affect the mean is by looking at the EP flux, which is a mathematical expression derived from distributions of eddy temperature and momentum fluxes, and is related to the eddy potential vorticity flux. In this perspective, everything 'eddy' would include some of such things as (internal) gravity waves, (internal) intertia-gravity waves, Rossby waves (baroclinic waves, planetary waves, etc.), equatorial Rossby waves, Rossby-gravity waves, and Kelvin waves; thus these can all have eddy fluxes. I'm a bit vague on much of this, but the gist of what I've gotten is: These waves can propagate through the atmosphere in some ways; depending on the type and at least sometimes the wavelength of the wave, there can be a index of refraction assigned to parts of the atmosphere which is a function of the wind field, the coriolis effect (varies with latitude), stability, and/or quantities derived from those things - vorticity, potential vorticity, etc. Waves may propagate horizontally only or they may also propagate vertically. Relevant to either direction, there can be critical levels. There may be regions where the wave can not propogate in an oscillatory manner - upon reaching a boundary it may be felt on the other side as an evanescent wave, one which decays exponentially away from that boundary - if another boundary is reached where it can again propagate, perhaps some of it will have tunneled through the barier (perhaps analogous to electron tunneling, considering the quantum-mechanical wave nature of electrons; also perhaps analogous to the evanescent portion of an electromagnetic wave which exists on the opposite side of a reflecting surface). Some gravity waves are actually evanescent waves - for example, a gravity wave produced by wind blowing over a ridge may decay with height and have vertical phase planes vertical with - zero group velocity? - whereas otherwise a gravity wave produced by wind blowing over a ridge will propagate vertically (the energy will propagate with the group velocity, and this carries momentum). Waves may be concentrated by variations in the index of refraction. They may reflect. They may over-reflect - I'm not sure but maybe that's analogous to the stimulated emission of radiation. Generally, disturbances may radiate waves. Waves may grow, and thus must be taking something from the background state they inhabit. They may dissipate, and in doing so they may deposit momentum back into a background state. Waves can also break (like waves crashing on a beach). I started going into this because wave-mean interactions are important in the global circulation; wave propagation also is important in stratospheric and mesospheric motions; etc...
130795. Mizimi at 05:49 AM on 29 October 2008
        Temp record is unreliable
        Thanks Chris; somehow I missed the link. This thread is about temperature records and how reliable /accurate/representative are they. CO2 levels are assumed to vary only slightly due to effective atmospheric mixing, but this is very different from temperature which has much greater variation. Given the paucity of temperature recording stations I cannot accept that the data used for models is sufficiently representative of the global condition, and thus the resultant of the model is questionable. Even satellite records are questionable as recently demonstrated by the modification needed to the attitude correction algorithm.
130796. chris at 05:46 AM on 29 October 2008
        Global warming stopped in 1998, 1995, 2002, 2007, 2010, ????
        Re #24: That's incorrect. The overall trend of the last 5 million years has been a mildly cooling one. Re #21 There's no such thing as "normal" temperature in relation to the Earth. The Earth is on a journey through time, and it's properties (atmosphere, temperature, biosphere, geology and so on) evolve according to a whole range of intrinsic and extrinsic factors. For human kind and the current biosphere, "normal" only really has a meaning in relation to evolutionary adaptedness. The biosphere in its current state is adapted (i) to the relatively cool period of the last several million years, and (ii) to a world with rather more continuous and connected environments that has, until the recent past, allowed migration as a fundamental means of adapting to climate change.
130797. chris at 05:31 AM on 29 October 2008
        Global warming stopped in 1998, 1995, 2002, 2007, 2010, ????
        Re #23 The notion that one can change reality or somehow diminish real world implications with semantics is a dismal notion...it's politics, not science. The world is warming..the evidence indicates that the massive enhancement of greenhouse gases is a dominant causal factor....our understanding of the climate system and its response to enhanced greenhouse effect indicates that we're very likely to get a considerable amount of additional warming. That's "global warming"...and it's already causing "climate change"... As for the "shift in emphasis" from "Global Warming" to "Climate Change", much of that "shift" has come from the sectors of the political spectrum, especially in the US, that has had such a degrading effect on the entire US sociopolitic during the last several decades: So, for example, it was Frank Luntz, the Republican party strategist, that urged Republican candidates in a memo some years ago, to use the phrase "climate change" rather than "global warming", because (in his words): "Climate change is a lot less frightening than global warming". At that time, Luntz's aim was to misrepresent the science and to play the "uncertainty" game ("there's no proof that cigarette smoke causes cancer"..."there's no proof that aspirin enhances the liklihood of Reyes syndrome in children".."there's no proof that CFC's denude high altitude ozone concentrations" etc. etc. ad nauseum). Happily, like an awful lot of people that combine politics with at least a semblance of honesty, Luntz has shifted his viewpoint, such that he said in an interview a couple of years ago: "It's now 2006...I think that most people would conclude that there is global warming taking place and the behaviour of humans is affecting the climate..." The take home messages are, first, that the natural world sadly doesn't bow to ones' political pursuasions (see King Canute's political advisors!), second, that on the supposed use of semantics to politicise/downplay real world consequences, one should be a little more careful in assessing where the politicizations are coming from.... ....and third, if one considers that it is appropriate to misrepresent and deliberately misunderstand the science in pursuit of political agendas, one might consider who is actually benefitting from one's contrived misrepresentation...one might discover at some future time that one was being treated as a chump to service someone else's agenda!
130798. Mizimi at 05:31 AM on 29 October 2008
        It's the sun
        FYI: University of Almeria (Spain): A study by Pablo Campra (published in the Journal of Geophysical Research)on the effect of greenhouses in western Almeria province reports an 0.3C/decade drop in temp over the last 25 yrs....roughly the same as the rise in temp for the rest of the world during that time. Western Almeria has over 30,000 hectares of plastic covered greenhouses supplying produce to European supermarkets. The plastic sheeting increases the local albedo, reflecting sunlight back into space. The plants grown also act as a carbon 'sink' absorbing around 10 tonnes of carbon/hectare...an annual equivalent of 300,000 tonnes of carbon.
130799. Mizimi at 05:18 AM on 29 October 2008
        What does CO2 lagging temperature mean?
        Chris: You have listed catastrophic events which cannot be predicted and occur infrequently; yes, they had an enormous effect ( from which life recovered) but in the scheme of things were relatively transient. As such they should be factored out of any attempt to model climate.
130800. chris at 21:05 PM on 28 October 2008
        CO2 measurements are suspect
        Re #9 The ocean isn't really "covered by a few ships". The oceans have a scattering of data stations in isolated islands (see map in the World Data Centre For Greenhouse Gases in John Cook's top article). It's pretty hard to see what your difficulty is. If we can measure CO2 in the atmosphere from a whole slew of data stations in isolated positions around the world situated away from urban centres, and these give rather similar atmospheric CO2 measures (yearly averaged), then we can be pretty confident that we are obtaining accurate and valid measures of the atmospheric CO2 concentration, particularly if we have extended time series that allows us to determine year on year variations in the level from individual sites. That's rather consistent with what we understand about the nature of atmospheric gases that are highly diffusive, and so are pretty well mixed on the annual basis. Of course it's important to monitor yearly averages if we wish to determine the year on year variation in atmospheric CO2 levels, since there are significant intraannual (cyclic) variations, especially in relation to the yearly cycle of plant growth and decay that is dominated by the N. hemisphere seasonal growing/decay cycle. And we do know what the CO2 levels west of the Brazilian rainforest are. We have data from Huancayo in Peru from various periods in the 1980's. These are within a few ppm of the global average from the ocean surface stations (or the Mauna Loa observatory). We have data from Easter Island that lies to the west of the Brazilian rainforest. Likewise these data are within a few ppm of the rest of the globally averaged data. I expect you can find more data from sites west of the Brazilian rainforest if you try (it really depends how interested you are in finding out this stuff). We do know what the atmospheric CO2 levels are in the Sahara. We have extensive data from Assekrem in Algeria in the N. Sahara, for example. The data are rather close to the atmospheric CO2 levels measured from the globally averaged data (or the Mauna Loa data). In other words wherever we look, we find a rather consistent set of atmospheric CO2 concentrations throughout the world, so long as these are measured in isolated sites unperturbed by major sources of atmospheric CO2.

Prev  2608  2609  2610  2611  2612  2613  2614  2615  2616  2617  2618  2619  2620  2621  2622  2623  Next