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Plugging the leaks

Filed under: — group @ 17 May 2012

Guest commentary by Beate Liepert, NWRA

Clouds and water vapor accounts for only a tiny fraction of all water on Earth, but in spite of it, this moisture in the atmosphere is crucially important to replenishing drinking water reservoirs, crop yields, distribution of vegetation zones, and so on. This is the case because in the atmosphere, clouds and water vapor, transports a vast amount of water from oceans to land, where it falls out as precipitation. Scientists generally agree that rising temperatures in the coming decades will affect this cycling of water. And most climate models successfully simulate a global intensification of rainfall. However, physical models often disagree with observations and amongst themselves on the amount of the intensification, and global distribution of moisture that defines dry and wet regions.



In a paper published in Environmental Research Letters, my co-author and I investigated these model discrepancies (Liepert and Previdi, 2012) (see also here). We developed a “quality control test” for climate models that is solely based on physical principles. We retroactively sum up all possible source, sink and storage terms of atmospheric moisture in models and postulate that a perfectly balanced physical model is a model without artificial leaks or floods in the system (note that small terms like methane oxidation fluxes into the atmosphere, or changes in total cloud water were not included). This approach of “self-consistency” is in contrast to previous studies where scientists performed model “reality checks” of comparisons with uncertainty prone precipitation observations. Eighteen state-of-the-art climate models as described in the United Nations 4th Assessment Report (IPCC-AR4) of the Intergovernmental Panel on Climate Change were included.

We found that most models predict an increase in moisture coming towards land in the course of the 21st century due to larger warming of land versus ocean surfaces with moderately increasing greenhouse gas concentrations. Some models, however predict radically opposite results, But these few models have large biases, which strongly affects the multi-model mean. The multi-model mean is often used in climate science and climate impact studies as “best predictor” since it smooths over model inconsistencies. These biases appear to be associated with ‘leaks’ in the model whereby water does not appear to be conserved. Some model leaks are even bigger than the anticipated global precipitation changes in the 21st century. The multi-model average is therefore biased by these few and has an average “leak” of the size of the discharge of the Mississippi river!

With our self-consistency test we were able to identify the outliers and narrow the prediction uncertainty. Only using the consistent models, we expect that in this century, the atmosphere will increasingly transport moisture towards land by the size of the river Nile, and with a model uncertainty of up to 13 percent of increase.

It is difficult for models to keep track of the small amount of water contained in the atmosphere (a thousandth of a percent of the total water on Earth). On the other hand, it is crucially important to plug leaks in physical climate models because water in the atmosphere plays an important role in the energy balance of the Earth. A bit fewer clouds, due to the leaks, can let extra solar energy reach the earth surface and heat up the planet – lost water vapor would have the opposite effect. This spurious energy flux in leaky models constitutes a “ghost” forcing of climate. We calculate that the ghost forcing in the IPCC models ranges from -1 to +6 watts per square meter, a forcing comparable to the size of non-carbon dioxide greenhouse gases – though since it is roughly constant in time it doesn’t impact the transient runs directly.

These results show that independent quality controls on climate model simulations are crucial for assessing the quality of future climate change predictions. Not all models are equally good and should be utilized in climate impact studies.

Climate impact models are used, along with crop yield, and hydrology models for instance, to inform far reaching decision-making. Climate research institutions are under pressure to build more accurate, more complex models that incorporate not only the physical climate, but also ecosystem processes and perhaps eventually, economic impacts. Testing and quality control should of course accompany these model developments, and it is to the credit of the modeling groups that they archive enough information in the public archives of CMIP3 and now CMIP5 that we can do these tests independently, assess the remaining problems and hopefully improve the predictions.


References

  1. B.G. Liepert, and M. Previdi, "Inter-model variability and biases of the global water cycle in CMIP3 coupled climate models", Environ. Res. Lett., vol. 7, pp. 014006, 2012. http://dx.doi.org/10.1088/1748-9326/7/1/014006

54 Responses to “Plugging the leaks”

  1. 1
    Joel Shore says:

    Two questions:

    (1) Does removing the “leaky” models from the multimodel mean significantly decrease the disagreement that Wentz et al. (?) found in terms of precipitation having increased more in the real world than the models predict?

    (2) Are the “leaky” models also outliers in any way in terms of their climate sensitivity (as shown in Table 8.2 of the IPCC AR4 report) or are they pretty much in line with the non-leaky ones?

  2. 2

    I’m looking forward to when the constraints on individual models achieve better constraints so as to strengthen the confidence. It would be nice to know what this ghost is up to/too.

    Where are the Ghostbusters when you need them?

  3. 3
    Dan H. says:

    John,
    Another paper shows problems in other models also.

    http://curryja.files.wordpress.com/2012/05/kim-et-al-2012_grl.pdf

  4. 4
    Beate says:

    We have shown in another paper Liepert & Previdi 2010 that the large precipitation increases in the last two decades shown in Wentz et al. can be explained by reduction in air pollution (reduced “global dimming”, some optimists call it global “brightening”!). And it would be simulated by the better models if the aerosol forcing were better constrained. This comparison is not necessarily a physical problem of models.
    Btw this is why we advocate for both types of model testing: consistency checks and reality checks.

  5. 5
    Beate says:

    There seems to be some correlation between leaking to sensitivity albeit not significant.

  6. 6
    John West says:

    “Only using the consistent models, we expect that in this century, the atmosphere will increasingly transport moisture towards land by the size of the river Nile”

    So, increasing Global river flow by 0.28% from 562,636 to 564,220 cubic meters per second (on average)?

    (Nile being 1,584 cubic meters per second.)

    http://www.rev.net/~aloe/river/

  7. 7
  8. 8
    Dan says:

    re:3. The paper “partly supports the utility of the multi-model ensemble approach in overcoming the systematic model biases from individual models and in enhancing decadal predictability.”

  9. 9
    Patrick 027 says:

    About ghost forcing: “though since it is roughly constant in time it doesn’t impact the transient runs directly.” – so just to be clear, this is a ghost forcing present in all forcing scenarios in the models and not a ghost feedback, right? (Now that I’ve asked the question I’m positive the answer must be yes, but maybe worth highlighting the point anyway?)

    Are there similar leaks in weather forecasting models?

    Somewhat off on a tangent but something I’ve wondered about – to what extent is the increased warming over land relative to ocean a transient response due to the ocean’s heat capacity including that of the deeper ocean? (And is the remaining (equilibrium) part of the increased warming associated with a decreased diurnal temperature range over land (which may not be the case everywhere…)?)

  10. 10
    Blair Dowden says:

    I am trying to understand the significance of “an increase in moisture coming towards land in the course of the 21st century due to larger warming of land versus ocean surfaces.” Comparing it to the outflow of the Nile river does not help very much. I would rather compare it to the direct effect of raising temperature and increasing the amount of water vapor in the atmosphere. It would also be nice to know what it really means to how the climate will affect us.

    I recall reading in these pages that the former wetness of the Sahara Desert thousands of years ago was due to more moisture arriving from the ocean. Was this caused by the temperature differential due to global warming in progress? And when the Holocene warming stopped, the differential lessened, and the Sahara became desert? Is this the kind of magnitude we are talking about here?

  11. 11

    #3 Dan H.

    There are problems with all models. Scientists root out the problems to improve the models.

    The real problem is when people, or even untoward propositions by certain scientists, highlight the uncertainties disproportionately in contrast to what is known… often grandstanding the points out of context for the deenialosphere.

    Now who would do such a thing… hmmm… Judith Curry perhaps? Roger Pielke Jr/Sr? S. Fred Singer? John Christy? Roy Spencer? Richard Lindzen, Patrick Michaels, Steve McIntyre, Ross McKitrick… et cetera

  12. 12
    Patrick 027 says:

    Re 8 Blair Dowden – The orbital forcings on Earth are primarily redistributions of TOA insolation (incident solar radiation at the Top Of the Atmosphere) over latitude and year, with the eccentricity variations having only a small effect on global annual average TOA insolation (although variations in albedo could take that redistribution and turn it into a global annual average change in solar heating) – glaciations and deglaciations can be caused by that because seasonal and regional changes can have global average effects (an ice sheet forming in one place can have a global average cooling effect; and then there’s CO2 and CH4, vegetation, etc.). But other regional climate changes can continue to occur with or without glaciations or deglaciations (such as when Earth’s global average surface temperature is desensitized to orbital forcing). I’ve read that the precession cycle in particular affects low-latitude monsoons and is responsible for those Saharan wet-dry variations (but the strength is modulated by eccentricity, and I don’t know that there isn’t a glacial-interglacial variation there). My understanding is that when eccentricity is sufficiently large and the summer solstice is sufficiently close to perihelion, there can be strong enough solar heating in the northern low-latitudes in summer to drive circulation to bring rain into the Sahara (and there’s a vegetative positive feedback).

  13. 13
    Patrick 027 says:

    Re the last part of my comment 7: The reason why I refered to DTR in the context of increased warming over land – I was trying to think of why land would warm more than ocean (aside from heat capacity) and the idea I had was

    Winds tend to be stronger in the free troposphere than in the boundary layer – or ocean currents (or average land surface motion, obviously), so different fixed locations (or slow-moving masses of surface water) ‘share’ the free troposphere more than the boundary layer. For the sake of illustration, consider the simplified case where the free troposphere is horizontally and temporally constant (it has a small DTR; relative to land surfaces the solar heating / heat capacity ratio is smaller), it will tend to be convectively coupled to places and times where the surface is warmest (for a given relative humidity) or otherwise more humid. When the land surface cools at night it can be decoupled (convectively) from the free troposphere, while it can only warm up to the point that it becomes convectively coupled (it would warm after that along with the free troposphere but not as much). With the ocean having nearly zero DTR, it should tend to warm up until it is also convectively coupled to the free troposphere, so it will be as warm as the warmest land surfaces, except if those land surfaces and their boundary-layer air are dryer (seems plausable depending on vegetation and soil moisture), and except if the export of latent heat toward land cools the ocean surface to the point that pure radiative equilibrium (with the given horizontal fluxes of heat) with the air above would be convectively stable. Thus increasing DTR over land could make the land surfaces cooler on average relative to the ocean (and increase global average lapse rate in the boundary layer ?); on the other hand, drying the land could make it warmer. And soil moisture affects DTR (as do cloud cover, H2O vapor, wind)… So either drying or decreasing DTR could (depending on what else is happening) result in greater time-averaged warming regionally (relative to other regions).

    Is this on the right track?

  14. 14

    #8 Blair Dowden
    #10,11 Patrick 027

    I can speak from my sailing experience in SoCal. Generally speaking and depending on what time of year it is, the land areas radiate off a great amount overnight and when the land dissipates enough heat to be cooler than the surrounding ocean, the breeze will be offshore. This is great so as to sail out in the morning.

    As the land heats up in the daytime and becomes warmer than the ocean, the rising heat column will draw air from the cooler ocean creating an onshore wind, which is great in the afternoon when you want to sail back into port.

    Of course frontal passage and direction can override or accentuate this effect.

    I don’t know the science around this very well, but I imagine that with warmer oceans evaporating more moisture and warmer lands drawing that moisture inland, then stronger rainstorms are feasible. Of course this would have to be considered with regional changes in the hydro-logic cycles due to pressure variances and myriad other factors including of course ocean cycles and changes on land due to increased temperatures.

  15. 15
    Unsettled Scientist says:

    Dan H. #3

    Your post is so devoid of content as to be meaningless. I really wish you’d at least put in the time to read the paper before you copy & paste it so you could say something of interest about it, even if your wrong about it at least it would be interesting. What kind of models? What kinds of problems? The kinds of problems that the author Judith Curry has with reality? That kind of problem? (Removing tongue from cheek.)

    Reading the paper myself, it looks as if the authors are saying that areas in which single or coupled models are lacking skill, using a multi-model ensemble (MME) one can improve the forecasting skill in those areas (notable AMO, PDO and global mean temperatures).

    So it’s not really “models have problems”, but more like “using the models together makes them better” in extreme vernacular.

  16. 16
    David B. Benson says:

    Thank you, Beate.

  17. 17
    tharanga says:

    I am enjoying the guest articles – it is good to get people with different expertise and perspectives on here. Please continue to invite them.

  18. 18
    Chris Colose says:

    Patrick,

    You’re right that the thermal inertia is not the whole story for the land-ocean contrast (land is still amplified considerably even in equilibrium experiments). Manoj Joshi has a couple papers, notably one with co-authors in 2008 in Climate Dynamics, discussing several relevant mechanisms.

  19. 19
    Christopher Hogan says:

    The question I would like answered is this: What does this mean, if anything, for predictions of drought conditions in the US interior, this century, e.g., per Dai’s 2010 review?

    At first glance, reading this research, while individual models deviate substantially from “conservation of water”, for whatever reason, the ensemble median is close to being neutral. So to an uninformed reader like me, the main thrust of this seems to be narrowing the uncertainty around the existing mean prediction, rather than shifting the mean.

    So, does the imposition of self-consistency on all models materially change Dai’s prediction of likely widespread North American drought this century? Or does it mainly narrow the uncertainty (and slightly shift) that mean prediction, in effect saying that we’re even more sure of this outcome?

    As a resident of North America, that’s the practical takeaway from this that I would like to know.

  20. 20
    Patrick 027 says:

    Re 18 Chris Colose – Thanks!

  21. 21
    Sou says:

    @Christopher Hogan #19 – That’s an important question and not just for the USA. As I read it, the article doesn’t indicate the pattern of precipitation, only the likely trend in total precipitation.

    So far from what I’ve observed the trend here is for more intense droughts and more intense precipitation. This seems to be supported by the literature I’ve read.

    If there is even more precipitation on land (resulting from ‘larger warming of land versus ocean surfaces’), as seems to be indicated by the article, then droughts and floods can both increase as greenhouse gases accumulate – with different regions responding differently.

    We are starting to get local climate projections here now, and where I live that pattern is what is expected. In addition the seasonal pattern is expected to change, which means local agricultural production will have to adapt quite a lot. (Other parts of Australia have different projections – particularly in the tropics and sub-tropics.)

    http://www.climatechange.vic.gov.au/regional-projections/north-east

  22. 22
    BaitedBreath says:

    o/t
    An idea I’ve seen floating around lately, is that although there is a decade+ hiatus in atmospheric warming, the (top 700m of the) oceans continue to warm.

    So is there some way that (atmospheric) CO2 could be warming the oceans without first warming the atmosphere itself ?

  23. 23
    CM says:

    Thanks for the post. As a general reader with little knowledge of mathematical models, I was left wondering how water could ‘leak’ out of one. I’d naively think that one could just decree that water be conserved, and it would be. You referred to the very small amounts involved — is it something like rounding errors?

  24. 24

    I suspect that as regional-scale prediction becomes quicker, easier and more accurate sensible voices will become more prominent in the discussion–it will be a much more pragmatic discussion overall. And precipitation will be a big part of it.

  25. 25

    #22–Sure–the CO2 modifies the atmosphere’s radiative properties, not its heat content directly.

  26. 26
    BaitedBreath says:

    #25
    So CO2 absorbs LW, but is never warmed by it? ALL the LW it absorbs, is reemitted (in all directions, some of it downwards)?

    And the oceans also absorb (the downward) reemitted LW, but ARE warmed by it ?

    [Response: This discussion is confusing people! Yes, CO2 is warmed by the absorption of long wave, so yes, the atmosphere heat budget DOES increase as a result.–eric]

  27. 27
    Ray Ladbury says:

    BaitedBreath,
    This is a wee bit off topic, but:
    CO2 high in the atmosphere is cool, and so largely in its ground state. It absorbs IR radiation from the surface and goes into a vibrationally excited state. This state can relax either radiatively, or by undergoing a collision with another molecule (most likely N2), which passes energy to the N2, heating the atmosphere. The latter collisional relaxation is far more likely in the atmosphere, so re-radiaton of IR occurs for only a minority of IR captured. Keep your eye on the energy.

  28. 28
    dbostrom says:

    Apparently some of the leakage may be sprinkling over the midwest United States?

    Doubled Trouble: More Midwestern Extreme Storms (via Rocky Mountain Climate Organization and NRDC so contrarians should feel free to ignore the factual data contained therein, possibly at their own peril).

  29. 29

    BaitedBreath, the greenhouse effect is just like nuking a burrito in a microwave oven.

  30. 30
    Hank Roberts says:

    Many places in the US Southwest and other parts of the world have seen development building on old landslides, and old debris cones below steep ravines.

    Those seemed inactive, the slopes hadn’t moved for centuries.

    Those were mostly formed early after the last ice age ended, when warming and an increase in precipitation happend fairly quickly.

    Now, we’re getting faster warming.

    More precipitation events that are short and intense to follow?

    Insurance companies find this sort of observation interesting.

  31. 31
    ozajh says:

    John P. Reisman #14,

    I am not a scientist, but I believe you are correct about the likelihood of stronger (but possibly far less frequent) rainstorms. However, with increased temperature goes an increase in evaporation rate, with implications for plants’ water requirements. And agricultural (in its widest sense) fresh water requirements are FAR larger than everything else put together.

    I believe there is also the likelihood that the rainfall will increase in areas that already get more than enough, and decrease in the zones that area already deficient. In Australia there are HUGE differences in agricultural land values on a per-acre basis compared to places like the UK, and these differentials almost always boil down to rainfall and/or access to irrigation water.

  32. 32
    Ron Manley says:

    This is an interesting contribution. What I find most surprising is that it has not been done before.

    By my calculation water in the atmosphere weighs on average 1.28 E+13 tonnes. The annual flow of the Mississippi is 5.3E+11 tonnes. So, models lose 4% per year of their water. What is more the flow of the Nile is 1/6th of the flow of the Mississippi so models which lose 4% of their water every year are being asked to represent a process, transfer to land areas said to be equivalent to the Nile flow, of 0.07 % a year.

    As the authors correctly point out misplacing water is equivalent to losing energy – and the amounts are not trivial relative to other forcing mechanisms.
    I market the most widely used hydrological model in the UK (HYSIM). In that model I calculate the water balance at the start of simulation, inputs and outputs of moisture during simulation and the water balance at the end of simulation as check that it does not ‘leak’ (or ‘absorb’) water. It would seem to me axiomatic that climate models should at least do the same plus, possibly, an energy balance.

  33. 33
    Hank Roberts says:

    Are the two approaches described the same?

    This (main post) globally:
    “… a “quality control test” for climate models that is solely based on physical principles. We retroactively sum up all possible source, sink and storage terms of atmospheric moisture in models and postulate that a perfectly balanced physical model is a model without artificial leaks or floods in the system”

    and

    This (Ron Manley) for — just the UK in isolation?:
    “… calculate the water balance at the start of simulation, inputs and outputs of moisture during simulation and the water balance at the end of simulation as check that it does not ‘leak’ (or ‘absorb’) water.”

    If those don’t describe the same approach, what’s different?

  34. 34
  35. 35
    Ron Manley says:

    Hank Roberts #33

    1. Although HYSIM (the model) was developed in the UK it has been used successfully by me, colleagues and clients all over the world. Your “UK in isolation” comment does not apply.

    2. “What’s different” is that in my model the important water balance check is built-in whereas the paper by Liepert and Previdi shows that in (most? all?) climate models it is not.

  36. 36
    Susan Anderson says:

    I can’t help but think those water spheres are a little misleading. If you were to represent earth’s surface land in a similar way, how big would it be? Of course, it would involve a decision as to what to include or not, but the visual while initially stimulating is beginning to bother me.

    Also, I’m always puzzled by people who treat various kinds of water events and absences as discrete from each other. There are extreme events, both dry and wet, and a whole host of things in between. Anyone who lives in areas that have pleasant livable proportions of wet and dry can observe that drought and flood is changing on a much smaller, but still damaging scale. In addition, flooding events can disturb the process that keeps our water clean and leave mold and other toxic effects behind. All these changes add up, a little bit here, a little bit there, to steady disturbance of the processes that we have come to take for granted.

  37. 37
    Marcus says:

    #35 Ron Manley:

    The hydrology tool serves a different purpose than a climate simulation. It is trivial that the continuity equation has to be fullfiled exactly as movement of water through land is calculated as a result, and the overall balance is a test, that no systematic shifts occur distorting the very result one is about.
    In a climate model that leaks water, the question is how does it leak and where. It has not been the main purpose of such models to display movement of water on land, for instance, and it is by no means clear that (working hypothesis) deficitary treatment of water continuity somewhere in the code implies a significant erroneous pseudo forcing, as You want to suggest.
    As models evolve and climate impact studies become more demanding, one could expect some development regarding water continuity, but there is nothing around advising standard GCMs do not serve *their purpose*.

    Marcus

  38. 38
    Ron Manley says:

    #37 Marcus
    I agree that the objectives of climate and hydrological models are different. I also recognise that whilst the model I have been talking about is fairly complex as hydrological models go, 60,000 lines of code, it is simple relative to climate models. That said, from the forgoing discussion it appears that the ’leakage’ of climate models is of the same order of magnitude as the changes they are trying to estimate. That, at the very least, raises doubts about their use as a predictive tool. It would be interesting to repeat the exercise to see if they also ‘leak’ energy.

    [Response: Be careful not to over-generalise here – there are many of the models that conserve both energy and water to machine accuracy (including the GISS models). However, historically there have been many reasons why there have been slight leaks in coupled GCMs – they mostly occur because component models – like the atmosphere, or sea ice or ocean have made assumptions that are not important when the component is run independently, but that when they are coupled lead to slight inconsistencies in energy and water fluxes. This takes time to work through within a coupled system – and it’s notable that the biggest leaks occur in the newer models. But these issues can be quite subtle – look up Bitz and Lipscomb (1999) or Schmidt et al (2004) for discussions on this related to sea ice fluxes. However while the implications of these leaks on sensitivity to change are generally small, it’s worth nailing them down. – gavin]

  39. 39
    Ron Manley says:

    #38
    Thanks, Gavin, for the clarification.

  40. 40

    Echoing John West’s question.

    Why give numbers in “Niles” rather than Sverdrups? We’re all grownups here.

    One Nile appears to be order 0.01 to 0.02 Sv in agreement with West. For global runoff I’m finding numbers between 0.6 SV and 1.2 Sv, so the nonleaky-model perturbation appears very small. Smaller than one would expect in theory?

    “Evaporation from the global ocean is estimated to be ~ 13 Sv, and the precipitation sums to ~ 12.2 Sv. The difference of 0.8 Sv compares with the estimate of river input of 1.2 Sv. ”

    http://www.eoearth.org/article/Sverdrup?topic=49549

    So in terms of model water fluxes, it is little wonder that leaks appear that compete; the actual perturbation over land is order one part in a thousand compared with the global flux and a fortieth of the uncertainty in the global balance. It’s not obvious to me that this is either robust or consequential, even if there is a tighter model consensus with the “leaks” plugged.

  41. 41
    Harold Pierce Jr says:

    The most important physical mechanism that transports water from the oceans onto the land is the wind, which is not shown in the diagram. When wind moves over the surface of water, nitrogen and oxygen molecules and argon atoms impinge upon the surface and blast water molecules right out of liguid phase into the gas phase, i.e. the air.

    In some regions, tropical cyclones transport enormous amounts of water from the ocean onto the land. A tropical cyclone is a gigantic rotary flash evaporator. The annual monsoons bring life-giving water from the oceans onto land. When the monsoons fail there is food shortages and misery.

    I live in Burnaby BC, a major ciy in Metro Vancouver (aka, Lower Lotus
    Land). During the rainy season, which starts in Nov there is a continous stream of low pressure systems that orginate in the Gulf of Alaska and dump over 1000 mm of water at Vancouver Int. airport. In the Queen Charlotte Island, annual rainfall is measured in meters.

    At the equator the land is moving at about 1000 miles per hour and “slides” under the air. A parcel of moist air in Atlantic ocean off the coast of Brazil will be at the foothills of Andes in less than two hours.

    In winter the ocean off the coast of eastern North America is extremely cold. Yet a Nor’easter can transport enormous amounts of water out of frigid ocean and depsits it on land in the from of ice and snow.

    Would a slight increase in mean global temperature by few tenths of a deg C or in the concentration of CO2 in air by a few ppm have any effect on any of the above mechanisms? Obviously not.

    About fifty years ago I was playing five card stud in the back room of the Tea Cup Inn. At the showdown of one hand, a player turned over his hole card, showed a pair of wired jacks, and started reaching for the pot. Cecil the Hammer turned over is his hole card, and his hand showed wired kings. Cecil the Hammer then said, “Them jacks broke. Better get’em fixed.”

    The water cycle is broke. Better get it fixed.

  42. 42
    dbostrom says:

    Further to Harold’s remarks, it’s well known that evaporation of the oceans is vigorous in tropical regions not because surface waters are warmer in the tropics but instead because that’s where the greatest concentrations of oxygen, nitrogen and argon are to be found. In other words, most of the atmosphere lingers near the equators. That’s also why people living at higher latitudes (such as in Burnaby, B.C.) tend to be rather light-headed and confused at times; the air is simply too thin to consistently support demanding intellectual pursuits.

  43. 43
    Hank Roberts says:

    > At the equator the land is moving at about 1000
    > miles per hour and “slides” under the air

    Ah, then tropical warmth would be due to frictional heating?

  44. 44
    CM says:

    Gavin @38, thanks — that answers my #23 as well.

  45. 45

    #41, 42–Ah! So that’s why I’m so much smarter since moving to Georgia!

    However, the thin air does facilitate the waving of hands.

  46. 46
    dbostrom says:

    @45: Here in Seattle we find that a cannula w/bottled oxygen helps. Farther north the low partial pressure of oxygen becomes more challenging. Even farther “up” where the air pressure drops still more, boiling summer seas are a spectacular sight.

  47. 47
    afeman says:

    #42: The equator is also where the surface is moving fastest (compared to higher latitudes). The inertial velocity goes to zero at the poles, which is why water condenses and freezes there.

  48. 48
    Brian Dodge says:

    Harold, you have a leak in your energy budget; the N2, O2, Ar, that “blast” the water molecules off the surface lose kinetic energy. Some of the kinetic energy is imparted to the water molecule, some is left in the other gases, and some goes into disrupting the water-water bonds which give liquid water surface tension. This is stored in potential energy of water vapor molecules to rebond into liquid. The energy available from condensation(rebonding into liquid) is called latent heat. Because the total kinetic energy left over is less by the amount taken by the latent heat, the gas molecules(N2, O2, Ar, and now H2O) are moving slower, so the air above the surface has cooled – evaporative cooling. The kinetic energy of water molecules in liquid water is enough to “blast” some molecules off the surface as well, and they take energy with them.

    Here’s a simple experiment you can do at home with a styrofoam cooler, a thermometer, some plastic wrap, and a teapot. Heat up a quart of water in the teapot, pour it into the cooler, put the thermometer in the hot water, and record the rate of cooling. Do it once with the cover open, and once with the cover closed. I predict that the water will cool slower with the cover closed, because the evaporating water molecules can’t escape & will reach equilibrium where just as many condense and carry energy (latent heat) into the surface as the evaporating molecules carry away. All the heat loss will be by conduction through the styrofoam – which is used in coolers because it conducts heat poorly. Do the experiment a third time, but cover the surface of the water with plastic wrap. Is the rate with plastic wrap closer to with the cover closed, or closer to cover open? What portion of the heat is carried away by conduction through the styrofoam, convection in the air with the cover open but plastic film preventing evaporation; and how much does it increase when you have conduction, convection, and evaporation?

  49. 49
    Bob Loblaw says:

    I can’t help but wonder whether you people are 1.5 months too late, or 10.5 months too early. Can’t you keep all your talents in check until the April 1 edition of RC????

    The classic one is “At the equator the land is moving at about 1000 miles per hour and “slides” under the air.. Of course,we all realize the truth of this, with regard to winds – every place on earth only ever experiences winds from the east, and they are always at a constant speed dependent on latitude and never change due to anything else. All that high/low pressure stuff, and trade winds, and “westerlies”, and that famous phrase “the wind are calm” – that’s all our imagination isn’t it?

    Please, Harold Pierce Jr, tell me that you’re just pulling or legs?

  50. 50
    adelady says:

    No Bob, that’s not the problem.

    What I want to know is the gravity arrangement at the equator.

    How do all those umbrellas on tropical island beaches stay where they are in 1000mph winds?


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