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Comments 129451 to 129500:

129451. Mizimi at 09:12 AM on 7 November 2008
        It's the sun
        QM: Green plastic is not a good colour! better is simple translucent or the slightly 'bluish' UV stabilised pvc.
129452. Mizimi at 09:02 AM on 7 November 2008
        Water vapor is the most powerful greenhouse gas
        PS: I cannot find figures for agricultural irrigation and windage losses: some of that evapotranspiration would be offset by 'natural' plant growth, but to what extent is not clear, so that 1870 billion tonnes is probably a bit high.
129453. Mizimi at 08:58 AM on 7 November 2008
        Water vapor is the most powerful greenhouse gas
        Yup, got my powers mixed up! That should have been 25 billion tons. There are a large number of water usage sites which give estimates for various activities: Evaporation from reservoirs: 275cubic km/yr (275 billion tonnes) World industry: 90 cubic km/yr.....90 billion tonnes (which includes the world's 63,590 power stations) Agriculture 1870 cubic km/yr ( listed as evapotranspiration as they can't tell the difference) So a reasonable estimate for AWV added to the atmosphere is 2200 billion tonnes a year which otherwise would not be there. Which is a lot more than the CO2 added.
129454. Quietman at 07:15 AM on 7 November 2008
        It's the sun
        Re: "we look at the EVIDENCE that they might use to support their statements." I don't think so.
129455. Quietman at 07:12 AM on 7 November 2008
        It's the sun
        chris Nice dissertation on how CO2 can be absorved by the ocean. Now show how much is tectonic. The fact is that you can't. This is an area that is not well understood. This is indeed claiming to know what we actually know very little about. 1) CO2 relaesed from undersea volcanos and ridges is direct to the oceans. 2) Fertilzer entering the oceans causes algal and bacterial blooms which then die, rot and produce methane and add carbon direct to the oceans, at the same time reducing O2 production. There are knowns but the actual amounts are total unknowns. Go ahead, please tell me that mankind knows everything that happens under the oceans. Then go tell the scientists that are still trying to figure it out, I am sure they would greatly appreciate it. You just don't get it. As much as we may know there are many times as much things that we do not know and pretending to know will not help.
129456. chris at 05:12 AM on 7 November 2008
        It's the sun
        Re #192 I'm don't understand the rest of your post. What articles are you referring to? As for your non-sciency assertions about Rhodes Fairbridge and "Spencer" (Spencer Tracy?!), I can't glean what you're referring to in the context of my post or this thread. Whatever you are referring to, we don't evaluate the assertions of others using hero-worship or personal preferences. Instead (if we are interested in the science), we look at the EVIDENCE that they might use to support their statements.. Your assertions about peer review and "fear" are not very intersting, since they're just conspiracy theory bluster and without any foundation whatsoever! Let's try to scientific and skeptical!
129457. chris at 05:01 AM on 7 November 2008
        It's the sun
        Re #192 That's quite incorrect Quietman. We know very well that our emissions are forcing up the oceanic CO2 concentration by prodigious amounts. We can measure this in a number of ways. We know quite well the scale of our emissions and can determine that around 40-50% of these have remained in the atmosphere. Much of the rest has gone into the oceans. We know that this has to occur from simple understanding of physical equilibria (Le Chatelier's principle). And we can measure this directly through analysis of inorganic carbon in the oceans, or via the reduction in ocean pH [see abstracts of Sabine et al (2004) and Feely et al (2004) below, for example]. There are many measures that demonstrate without question that we are pumping CO2 into the atmosphere in massive amounts and that this is disturbing the CO2 equilibrium between the atmosphere and the oceans well towards oceanic CO2 dissolution and dissociation into bicarbonate, and H+: CO2(air) <->CO2(aq)<-> H2CO <->HCO3- + H+ <-> CO3-- + H+ That's very well understood and characterised in the real world. We really shouldn't pretend not to know what we do know very well! Sabine CL et al (2004) The oceanic sink for anthropogenic CO2 Science 305, 367-371. Abstract: "Using inorganic carbon measurements from an international survey effort in the 1990s and a tracer-based separation technique, we estimate a global oceanic anthropogenic carbon dioxide (CO2) sink for the period from 1800 to 1994 of 118 +/- 19 petagrams of carbon. The oceanic sink accounts for similar to 48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO2 to the atmosphere of about 39 +/- 28 petagrams of carbon for this period. The current fraction of total anthropogenic CO2 emissions stored in the ocean appears to be about one-third of the long-term potential." R.A. Feely et al (2004) Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans Science 305, 362-366. Abstract: "Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans. This acidification process has changed the saturation state ofthe oceans with respect to calcium carbonate (CaCO3) particles. Here we estimate the in situ CaCO3 dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO2 on CaCO3 shell–forming species. CaCO3 dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO3 dissolution rate for the global oceans is approximately 0.5 ± 0.2 petagrams of CaCO3-C per year, which is approximately 45 to 65% of the export production of CaCO3."
129458. chris at 04:34 AM on 7 November 2008
        Water vapor is the most powerful greenhouse gas
        I wonder if your numbers are incorrect Mizimi. The total yearly worldwide emissions of CO2 are something a bit under 30,000 million tons [***]. I suspect your 25,000 billion tons of water vapour evaporated in cooling towers should similarly be 25,000 MILLION tons and not 25,000 billion tons. Where did your numbers come from? [***] see table 3 at: http://www.eia.doe.gov/oiaf/1605/ggrpt/
129459. Patrick 027 at 12:03 PM on 6 November 2008
        Arctic sea ice melt - natural or man-made?
        If you need anything clarified, please ask. (There's a lot I don't know but I'll try.) Books: I'm quite surpised that Cushman-Roisin is so expensive. You may want to look into Holton (An Introduction to Dynamic Meteorology). Two other books (these focus on the midlatitude weather): Mid-Latitude Atmospheric Dynamics A First Course - Jonathan E. Martin and Synoptic-Dynamic Meteorology in Midlatitudes Volume II Observations and Theory of Weather Systems - Howard B. Bluestein The second starts off without introduction to atmospheric physics; I think you could start with Volume I but I don't think you'd need it if you have either Holton, Martin, or maybe Cushman-Roisin. Bluestein, Martin, Holton, and Cushman-Roisin are all focussed on dynamics; of those, Cushman-Roisin gives the most attention to oceanic dynamics as well as atmospheric dynamics. There is also: Atmospheric Science An Introductory Survey - John M. Wallace, Peter V. Hobbs This is a very general book, which even discusses atmospheric electricity and the magnetosphere, as well as radiation, cloud microphysics, and the general circulation. Just the last two chapters (in the edition I have, anyway) go into mathematical detail regarding momentum and dynamics. Global Physical Climatology - Dennis L. Hartmann As with Wallace and Hobbs, a variety of subjects are covered; the distinction is a focus on climatological aspects here. Includes a chapter on oceanic circulation. Also discusses paleoclimatology, natural changes and anthropogenic changes, and climate models. (Which reminds me, Holton has a chapter about numerical modelling) Other books, a little less heavy on the detailed math: Earth's Climate - Past and Future - William F. Ruddiman The title says it all. A lot of good information. Essentials of Meteorology An Invitation to the Atmosphere - C. Donald Ahrens. An introductory level, perhaps too introductory if you've understood a fraction of what I've been saying (then again there are some good climate maps in the back and other interesting things). Snow Ball Earth - Gabrielle Walker For geology books that have some paleoclimatology in them, there's: Evolution of the Earth - Dott and Prothero Ontario Rocks - Nick Eyles
129460. Quietman at 10:10 AM on 6 November 2008
        It's the sun
        chris On CO2 entering or exiting the water. That is an assumption. There is no way to know if that is a fact. You like to say lets not pretend to not know what we do know. In this case lets not pretend to know what we dont know. Given the current state of tectonic activity under the surface of the oceans there is no way in hell you can know what direction CO2 is travelling. Did you actually read any of the articles that I gave links to? In this same argument at Live Science I was challanged to provide just 20 papers by scientists refuting AGW. When I provided links to 20 papers (not articles) I got the response that over half were not peer reviewed. They were not peer reviewed because of fear. This buddy review system means that if you don't agree you must be wrong. Rhodes Fairbridge was wrong because he was not peer reviewed. Here's a news flash for you, he was not peer reviewed because he had no peers. The man was a genius. Spencer gets knocked for his religious beliefs. I don't share his belief but I don't call him crazy for it. That is what is known as grasping at straws.
129461. Quietman at 09:48 AM on 6 November 2008
        It's the sun
        rob Your comment 188 had me laughing. Not at you however. It's the way you worded your statement. I do appreciate a good jab on occasion.
129462. Quietman at 09:41 AM on 6 November 2008
        It's the sun
        Mizimi I was thinking of safety, my grandchildren are 6, 4, 2 years and the latest 3 weeks old. I don't want to see them fall into a plain glass pane. I had in mind green translucent fibreglass for the roof and clear double pane 3'x 5' anderson casements mounted sideways for the walls. The andersons wont cost anything as they are currently on the house and I am replacing them with something easier to maintain. It's the roof panels that I am not sure about. Any thoughts?
129463. Mizimi at 06:35 AM on 6 November 2008
        Water vapor is the most powerful greenhouse gas
        Around 55% of the world's electrical energy is produced from coal (some 8 terawatts) and during that generation the approximate amount of water evaporated from cooling towers is about 25 million million tons/yr. or 25,000 billion tons...much the same as the CO2 from ALL fossil fuel combustion. And that figure does not include the water produced by combustion. The amount of WV varies according to time of day and load/location and network switching; but as coal fired stations are more difficult to modulate, they tend to be run as 'mainstay' providers, with oil or gas stations 'topping up' as necessary. That WV is generally enitted at around 100 to 200 meters above ground ( dependent on the type of cooling tower) and then drifts according to prevailing wind. That drift can exceed 2000 kilometers in 7 days ( average time before precipitation). So the next door country tends to get your WV ( rather like acid rain). Also, in another thread, Dan Panburn mentioned a paper which suggests the re-radiation of IR occurs within about 100 mtrs of the emitting body and thereafter conduction/convection take over. If this is the case, then adding substantial amounts of WV at relatively low altitudes would have an immediate warming effect which perhaps would be limited geographically by the WV 'shadow'. ????
129464. Dan Pangburn at 15:16 PM on 5 November 2008
        Models are unreliable
        Chris apparently has no knowledge of dynamic system theory. That helps explain the overt hostility (under the false assumption that I am just making stuff up) and why he/she mistakenly declares that some of my assertions are erroneous. Dynamic systems with feedback are phenomena of the natural world, like thermodynamics, genetics, cosmology, etc. etc., which can be studied and understood. The subject is studied by some engineers; usually as part of a post graduate course. They study the phenomenon and learn concepts and applicable mathematic tools and usually apply them to things like the guidance system of an antimissile missile, cruise control device for a vehicle, etc. Learning about dynamic systems is not required for climate scientists. They appear to be totally unaware that knowledge of dynamic systems would drastically alter their perception of world climate. Knowledge of dynamic systems allows recognition that world climate, as summarized by average global temperature, can be viewed as a dynamic system and that the mathematics and concepts of dynamic systems apply. Some things are immediately obvious to anyone familiar with dynamic systems with feedback. For example, the existence of temperature downtrends proves that significant NET positive feedback does not exist. Failure of climate scientists to recognize this stems from a lack of knowledge of that part of science pertaining to dynamic systems. Incidentally, a lack of knowledge of dynamic systems resulted in misinterpreting the meaning of ‘input’. Input to a dynamic system refers to the input to the transfer function. This input is not merely the output of the source of energy (as Chris erroneously guessed), which in the case of climate is the sun, but also includes any and all feedbacks (the combined effect of which is NET feedback). Also, lacking an understanding of dynamic systems can result in the delusion that world climate is somehow special and does not follow the same (dynamic system theory) rules as other dynamic systems. The output of this dynamic system model is average world temperature. The transfer function is by definition a function that accounts for all factors that influence average world temperature. Lack of understanding of dynamic systems with feedback has resulted in a repeat of stuff that no one that is knowledgeable on the subject disputes and a failure to realize that temperature downtrends prove that substantial negative feedback must exist because the NET feedback can not be significantly positive. Temperature observations are widely available. They show temperature downtrends when there is no significant influence from Milankovitch. This could not take place (without change to influence from outside the planet) if there were any net positive feedback. Without the imposition of net positive feedback by the GCM users, the GCMs do not show significant global warming. Other shortcomings of GCMs and their use are described at 32 above. Any good reference on dynamic system theory and application would serve to learn how dynamic systems work. As a start, one might review the applicable chapters in Phelan, R 1967, Dynamics of Machinery McGraw Hill Book Co. NY. Although the subject is presented in the context of control systems it is readily generalized to apply to global climate and global average temperature.
129465. chris at 06:29 AM on 5 November 2008
        The Mystery of the Vanishing Ocean Heat
        Re #24: HealthySkeptic - Thinking of something silly and then asserting that that's what the scientists must have done, isn't skepticism…it’s not healthy either – allowing yourself to be used as conduit to service someone else creepy agenda is not good for you! …There are lots of problems with your little post: (i) The IPCC doesn't make measurements, and I'm pretty sure it didn't "choose a location like Hong Kong, which is subsiding, to collect sea level data" (can you source that idea please?). Scientists make measurements, and they publish their data. The role of the IPCC is to make a detailed compilation of the scientific data and to present this in reports such that the complex science can be appraised by policymakers and the public alike. (ii) The data on sea levels from tide guages, comes from 100's of tide guage locations. In fact there are probably 1000's of these, but since it would be foolish to use tide guage measurements from regions where the geophysics, in relation to isostatic post glacial rebound effects or subsidence, is poorly defined, many of these are eliminated from analysis. So as Douglas and Peltier stated in a review some years ago: "Tide guages in Alaska, Japan, India, and many other areas have long records that are unusable because of vertical uplift or subsidence associated with seismic activity or crustal deformation" BC Douglas and WR Peltier (2002) The puzzle of global sea-level rise. Physics Today 2002, 35-40. And so, for example, a recent analysis of the rate of sea level rise throughout the 20th century century analyzed data from a set of tide guages that numbered around 50 in 1900, rising to around 100 in 1940 and 300 in the 1990's. Tide guages data were only used where reliable assessment of non-sea level change contributions were determined either to be minimal or assessable [*] [*] J. A. Church & N. J. White (2006) A 20th century acceleration in global sea-level rise. Geophys. Res. Lett 33, art # L01602 (iii) The IPCC isn't trying to "prove" anything. Its role is to summarise the scientific data periodically so as to inform policymakers (and anyone who cares to take advantage of an incredible resource) of the science. I suspect that it might be you that is trying to "prove" something! Anyway it's very easy to compare the IPCC reports with the original scientific data, and so (if one is sufficiently interested) to determine whether the IPCC reports are a faithful assessment of the science.
129466. chris at 04:07 AM on 5 November 2008
        It's the sun
        re #186/187 rob, the sun certainly keeps us snug, but it hasn't made any significant contribution to the marked warming of the last 30 odd years! (i) remember that the paper that indicates high solar activity "over the past 60 years" in the context of the previous 1150 years (Usoskin 205; link in John Cook's top post), only addresses the relationship between solar output and the Earth's surface temperature up 'til 1975. Since that time the solar output has been tending downwards a tad, while the Earth's surface temperature has gone up markedly. As the authors indicate, variations in solar outputs can't have made a significant contribution to the marked warming of the last 30-odd years. (ii) Storage heaters once warmed up and disconnected from their energy supply do continue to release heat through the next day (they're full of bricks!), but the maximum heat release after disconnecting from the mains occurs immediately, and then drifts downwards (an exponential decay of release of thermal energy as the heater tends towards a new equilibrium temperature equivalent to ambient temperature - it's slightly more complicated since the ambient temperature isn't constant and in any case is (hopefully!) responding to the hot bricks). So the oceans may release thermal energy stored following a period of high solar output, but the maximal rate of release of thermal energy should occur pretty soon following a downward drift in solar output, and this release of thermal energy will drift downwards much like your storage heater. However that's completely contrary to the temperature record. The solar output maxed around 1950, and since then has been pretty constant, drifting downwards a tad in the last 20-odd years [see, for example, Mike Lockwood and C. Fröhlich (2008) "Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. II. Different reconstructions of the total solar irradiance variation and dependence on response time scale"; Proceedings of The Royal Society A 464, 1367–1385; as well as the long list of similar studies linked in John Cook's top post under "Other studies on solar influence on climate"]. A storage heater doesn't hold onto all of its heat for a long, long period before starting to release it. Neither does the ocean. (ii) Another difficulty with your argument relates to the "top of the atmosphere" radiation budget. I’m pretty sure that satellite monitoring of solar irradiation and that returning from space shows an imbalance (‘though need to hunt down the relevant papers). There's excess solar energy being retained in the climate system, consistent with greenhouse gas warming. If the warming was due to some magical delayed release of stored thermal energy in the oceans, one would expect a top of the atmosphere balance of solar and re-radiated energy, or even a slight excess dissipation of energy into space. I don't think the data supports that interpretation. (iv) Notice that the temperature hasn't declined since 1998. The temperature has been on a rising trend from the mid- 1970's, through the 1980's, 1990's and early 2000's. The surface temperature in 1998 was lifted by around 0.2 oC above the trend by the strongest El Nino of the 20th century [see, for example: http://data.giss.nasa.gov/gistemp/2005]. In such an event solar thermal energy absorbed by the ocean surface is anomalously spread over vast tracts of the Western Pacific and Indian ocean to the Eastern Pacific and the S. American coast, combined with the suppression of cold water upwelling along the Western S. American coast. This gives us a marked but transient upward jump in the Earth's surface temperaure. In 2005 we pretty much reached the 1998 surface temperature without the large temperature enhancement of a strong El Nino. So the temperature was still trending upwards through 2005... (v) Note also that the increased surface temperature resulting from enhanced greenhouse gas concentrations relates to the new equilibrium temperature corresponding to the Earth’s new “balance” in response to an enhanced forcing. But of course both at equilibrium, and during the “journey” towards the new equilibrium, stochastic (and non-stochastic) elements of the climate system introduces “noise”. So we don’t expect a perfect progressive increase in temperature as greenhouse gas concentrations rise. We only have to look at the temperature record to see that the marked warming of the last 30-odd years constitutes a rising trend “overlaid” with noise that takes the year on year temperature on short upwards and downwards excursions. (vi) Note also that while changing solar output or the very slow cyclic drift of the Earth's orbital properties that underlie the ice age cycles does cause CO2 to re-equilibrate somewhat from the oceans to the atmosphere, this effect is very, very small in the context of current rising atmospheric CO2. So while atmospheric CO2 levels rose by around 90-100 ppm during the 5000 years of the last glacial to interglacial transition (in response to a temperature rise of around 6 oC), we've had a 70 ppm rise in atmospheric CO2 since the start of the 1960's. So atmospheric CO2 is rising more than 100 times faster now than during the ice age transitions that are the best example of your scenario of heat-induced release of CO2 from the ocean. And of course we known that CO2 isn't coming out of the oceans in response to warming. CO2 is being forced INTO the oceans in prodigious amounts.
129467. Quietman at 12:04 PM on 4 November 2008
        Arctic sea ice melt - natural or man-made?
        "Introduction to Geophysical Fluid Dynamics" by Benoit Cushman-Roisin, 1 new from $361.71 9 used from $175.00 so I think I will skip this one unless the library has a copy.
129468. Quietman at 11:59 AM on 4 November 2008
        Arctic sea ice melt - natural or man-made?
        Patrick Thank you. The small part of that I managed to understand was interesting. Also thanks for the references. I will see if I can locate a used copy of "Introduction to Geophysical Fluid Dynamics" by Benoit Cushman-Roisin as it sounds like it may illuminate some questions I have.
129469. rob at 11:38 AM on 4 November 2008
        It's the sun
        chris at 09:48 AM on 7 October, 2008. If CO2 is the driver why has the temperature declined since 1998 when CO2 is still increasing. It`s the sun you fool, sun warms the oceans, which warm the land mass, you know, the gulf stream, warm oceans release CO2, sun goes dormant, oceans cool, land temps decline, CO2 also begins to decline, simple.
129470. rob at 11:26 AM on 4 November 2008
        It's the sun
        Might the heating of the oceans (which cover 75% of the planet and are the largest heat reservoir on the planet) by a sun that has been more active over the past 60 years than anytime in the previous 1150 years have something to do with the continuing rising temps from the late 1970`s till 1998. You know common sense, err, storage radiators of the 60`s, heat them up at night get heat all through the next day. Are you dumb enough to expect all the accumulated heat in the oceans to disappear overnight just because the heaters been turned off, of course the correlation is still sound. Pity you did not show the graph ending at 2008.
129471. Patrick 027 at 05:08 AM on 4 November 2008
        Arctic sea ice melt - natural or man-made?
        Returning to isolated vortex superimposed on pv or av gradient: One can see (unless the following is wrong*) that there must be some tendency for the relative vorticity 'center' to be displaced from a center of total state PV or AV; with basic state PV or AV increasing to the north, then (in the northern hemisphere) a cyclonic PV/AV anomaly has an associated relative vorticity (RV) anomaly that is displaced to the south relative to the higher PV/AV values in the total PV/AV 'bump', so the wind field will advect the PV/AV anomaly to the west. For an anticyclonic PV/AV anomaly, the RV anomaly is displaced in the opposite direction from the lower values of PV/AV in the total PV/AV 'dent', but the direction of the winds is reversed, so again the anomaly is advected to the west. For a circular vortex, the wind decreases with distance. If the central PV/AV anomaly is balanced by a ring of opposite sign then the wind field can be even more limited. I started to draw this in the case of a vortex of entirely one sign of vorticity; Associated with the westward motion, the growth of anomaly to the west is of the same sign. There is growth of anomaly to the east which is of opposite sign, however (the energy of waves can propagate differently from wave phases by creation or growth of new phase lines). The anomaly growth is strongest along the east-west line where the anomaly winds are more north and south rather than east-west, and is inversely proportional to distance from the center, outside the region of initial anomaly PV/AV. Because of the rotation due to the variation in vorticity in two dimensions, the contours are distorted from a symmetrical wave shape. I have read that vortices may oscillate around their average propagation. The rotation could also cause the new anomaly phases to wrap around a bit, causing an overall tilt to phase lines and opposite tilt to the the extent of disturbances (??). If a vortex is strong or compact enough relative to the basic state gradient, as mentioned before, PV/AV contours may be closed; this tends to start off of center, toward higher basic state PV/AV for positive anomaly and opposite for negative (notice the potential geometric analogy to the trajectory/streamline relationships for propagating cyclones/anticyclones). To the extent that the PV/AV is conserved and not mixed, such closed loops, tending to act as material lines, can be though of as trapping fluid. Thus, unlike the essential aspect of waves, there is some fluid that must propagate with the disturbance. Also, for shorter wavelength Rossby-wave disturbances that might occur within the vortex, they would tend to propagate along such contours and would thus be trapped within the vortex. They might be able to tunnel out to some degree because the wind field can extend farther than the vorticity field; this will be more true for longer wavelengths than shorter wavelengths (the wind at a given distance being less sensitive to fine-scale vorticity variations). My understanding is that, to the degree that a vortex can radiate mechanical waves, it loses amplitude. If some mixing is allowed so that contours can reconnect, then this process could be associated to a vortex propagating towards greater basic state vorticity of the same sign (or reduced basic state vorticity of opposite sign), shedding it's outer layers, until the core eventually reaches basic state vorticity equal to the total vorticity within the original core. (If mixing is not allowed, this couldn't happen with the closed contour 'core' of the vortex - if it still propagates in the same direction, the countours would press up against each other, trapping, stretching and tinning out regions of other vorticity values.) --- Interesting questions: What about a checkerboard pattern of vorticity anomaly - proportional to cos(ly)*cos(kx)? What about such a pattern which is tilted at some angle? --- What about distortion of waves due to differential propagation and wind? The relative vorticity associated with a westerly jet is such that the poleward AV gradient is enhanced across a westerly jet; it is reduced across an easterly jet or relative minimum in westerly winds. (PS in case it wasn't clear before, a westerly wind is eastward (it comes from the west). A northerly wind is from the north. Etc.) Thus, Rossby waves' phase propagation through the air should be faster to the west within a westerly jet. This would oppose the tendency for the winds to carry the Rossby wave phases faster to the east within the jet. Supposing the advection of Rossby waves by the wind is the stronger effect: what would happen? To the north of a westerly jet, a north-south oriented wave phase line would become tilted northwest-southeast, and any that are tilted from northwest to southeast would be distorted such that the wavelength is reduced. Oppositely tilted waves would have their wavelengths increased and also get tilted toward being north-south. Mirror image on the other side of the jet. The zonal wave number is unchanged but the meridional wave number varies. ... Well without going into all the details, the effect, which would be different for different wavelengths, would be to alter the group velocities of the waves. Conceivably one portion of the spectrum might be pulled into a westerly jet (?)(causing it to meander with those wavelengths?) while another portion would be pushed away, and maybe the reverse for an easterly jet or relative minimum in the westerlies (?)
129472. 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.
129473. 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.
129474. 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.
129475. Patrick 027 at 06:13 AM on 3 November 2008
        Arctic sea ice melt - natural or man-made?
        Thanks Philippe!
129476. 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???
129477. 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 :-)
129478. 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).
129479. 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.
129480. 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)...
129481. 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)
129482. 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....
129483. 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...
129484. 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!
129485. 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].
129486. 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....
129487. 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?
129488. 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).
129489. 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...
129490. 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
129491. 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.
129492. 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...).
129493. 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...
129494. 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.
129495. 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!)
129496. 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...
129497. 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.
129498. 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
129499. 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"!
129500. 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...

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