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From: Bill Ward on 20 Dec 2008 02:28 On Sat, 20 Dec 2008 05:01:11 +0000, Don Klipstein wrote: > In article <pan.2008.12.09.00.55.04.957689(a)REMOVETHISix.netcom.com>, Bill > Ward wrote: >>On Mon, 08 Dec 2008 07:15:34 -0800, bill.sloman wrote: >> >>> On 8 dec, 05:42, d...(a)manx.misty.com (Don Klipstein) wrote: >>>> In article <tqb3j4pmpsqj32hes94kb9pni1vaup6...(a)4ax.com>, Whata Fool >>>> wrote: >>>> >bill.slo...(a)ieee.org  wrote: >>>> >>>> >>On 28 nov, 21:43, Whata Fool <wh...(a)fool.ami> wrote: >>>> >>> bill.slo...(a)ieee.org  wrote: >>>> >>> >On 27 nov, 23:02, Whata Fool <wh...(a)fool.ami> wrote: >>>> >>> >> bill.slo...(a)ieee.org  wrote: >>>> >>> >> >On 27 nov, 02:59, Whata Fool <wh...(a)fool.ami> wrote: >>>> >>> >> >> "DeadFrog" <DeadF...(a)Virgin.net>  wrote: >>>> >>>> <I snip to edit for space> >>>> >>>> >>> >> >You've misunderstood. The surface of the earth is ultimately >>>> >>> >> >cooled by radiation to outer space, but the "surface" that is >>>> >>> >> >cooled depends on the frequency that is being radiated. >>>> >>>> >>> >>    The frequency is determined by temperature, >>>> >>> >> isn't it? >>>> >>>> >>> >A black-body radiator emits a wide range of frequencies. The >>>> >>> >centre of the range does move to higher frequencies as the >>>> >>> >temperature of the emitter gets higher, but it doesn't move all >>>> >>> >that fast. >>>> >>>> >>>    Broadband radiation may resemble black body, but CO2 >>>> >>> does not radiate broadband. >>>> >>>> >>True, But it continues to emit at all the frequencies it can over a >>>> >>range of temperatures; >>>> >>>> >     The CO2 spectra is mostly narrow spikes, and >>>> > supposedly >>>> >those spikes are pretty much fixed to a certain range of >>>> >temperatures, show any reference that suggests otherwise. >>>> >>>>  The 15 um band of CO2 looks fairly broad here, comparable to the >>>> 2 broader water vapor bands at 6 and 2.5 um: >>>> >>>> http://www.iitap.iastate.edu/gccourse/forcing/images/image7.gif >>> >>> This spectrum covers a wide range of wavelengths, and doesn't ressolve >>> the rotational fine structure. >>> I've not had much luck finding spectra that do show the fine structure. >>> >>> The best I've been able to do is here >>> >>> http://www.anl.gov/PCS/acsfuel/preprint%20archive/Files/35_3_WASHINGTON%20DC_08-90_0738.pdf >>> >>> and since the pdf was generated by scanning a printed document, the >>> figures at the end of the document are none too clear. >>>> >>>> >     Actually, water vapor is almost BB at certain >>>> > temperatures, >>>> >that can't be said for CO2. >>>> >>>>  Water vapor has significant gaps. >>>> >>>> Same source: >>>>  http://www.iitap.iastate.edu/gccourse/forcing/images/image7.gif >>>> >>>> >>as it gets colder the number of phtotons emitted at shorter >>>> >>wavelegths goes down faster than the number emitted at longer >>>> >>wavelengths, which implies something rather from your "the frequency >>>> >>is determined by temperature". >>>> >>>> >   Exactly, so the net energy transfer is a function of >>>> > relative >>>> >temperature differences, say it anyway you want, but 388 parts per >>>> >million is a very small amount. >>> >>> But quite enough to repeatedly absorb and re-emit all the radiation at >>> the CO2 wavelengths as it goes through the atmosphere. >> >>Now what happens to the IR when it's absorbed? It goes to heat. Heat >>convects. > > Not where the local lapse rate is well below the relevant adiabatic one. > The temperature will get warmer than otherwise instead. Eventually it will convect, when the temperature rises enough. > >> That "re-radiation" bit is bogus. The gas is the same as any >>other, just warmer, and maintaining radiative equilibrium. I'm surprised >>you fell for that pinball explanation of radiative transport. IR travels >>at c. When it's converted to heat, it warms the gas, and allows >>convection to take place as soon as the lapse rate allows. > > If a layer opaque to longwave IR is added between the surface and what > the surface radiates to, then that new layer's temperature will be the > previous surface temperature. The surface will have to get warmer still > in order to transfer heat (from solar radiation) to that layer. Not necessarily, it can just transfer less heat at the same temperature. I just covered this in an earlier reply, so I won't repeat it fully, but if the layer is gas, it has a thermal conductivity, and IR is not usually considered part of the energy transfer through the layer in other applications. > Adding GHGs effectively does that to some extent. It adds a lower, warmer target. > Consider that most of the surface can get significantly warmer than it > is now before such a temperature rise initiates convection. But eventually it has to convect, if you keep adding heat. > > - Don Klipstein (don(a)misty.com)
From: Don Klipstein on 20 Dec 2008 21:16 In <pan.2008.12.08.09.55.26.820279(a)REMOVETHISix.netcom.com>, B. Ward said: >On Mon, 08 Dec 2008 05:06:34 +0000, Don Klipstein wrote: > >>In <pan.2008.11.30.20.54.34.361748(a)REMOVETHISix.netcom.com>, B.W. said: >>>On Sun, 30 Nov 2008 07:13:33 -0800, bill.sloman wrote: >>> >>>> On 29 nov, 06:43, Bill Ward <bw...(a)REMOVETHISix.netcom.com> wrote: >>>>> On Fri, 28 Nov 2008 19:25:22 -0800, bill.sloman wrote: >>>>> > On 27 nov, 20:50, Bill Ward <bw...(a)REMOVETHISix.netcom.com> wrote: >>>>> >> On Thu, 27 Nov 2008 07:50:47 -0800, bill.sloman wrote: >>>>> >> > On 27 nov, 06:32, Bill Ward <bw...(a)REMOVETHISix.netcom.com> >>>>> >> > wrote: >>>>> >> >> On Wed, 26 Nov 2008 17:09:40 -0800, bill.sloman wrote: >>>>> >> >> > On 26 nov, 22:17, Bill Ward <bw...(a)REMOVETHISix.netcom.com> >>>>> >> >> > wrote: >>>>> >> >> >> On Wed, 26 Nov 2008 07:53:11 -0800, bill.sloman wrote: >>>>> >> >> >> > On 26 nov, 12:28, Whata Fool <wh...(a)fool.ami> wrote: >>>>> >> >> >> >> Eeyore <rabbitsfriendsandrelati...(a)hotmail.com> Â wrote: >>>>> >>>>> >> >> >> >> >bill.slo...(a)ieee.org wrote:> >>>> >>>> <big snip - Bill Ward does go in for mindless repetition> >>>> >>>>> > Since the effective radiating altitude is 6km above ground, right in >>>>> > the middle of the troposphere, this seems to be exactly the right >>>>> > place for a radiative transfer model to be effective. >>>>> >>>>> There's an excess of water vapor available to convect latent heat up >>>>> to the effective radiating altitude. >>>> >>>> The air at the effective radiating altitude is well below the freezing >>>> point of water - the earth radiates as if it is a black body at -14C, >>>> and while this is an average over all wavelengths (for wavelengths >>>> absorbed and re-radiated by CO2 the temperature has to be closer to >>>> -55C) it makes sense that the radiation appears to come from a layer >>>> where water vapour - the predominant greenhouse gas - has condensed >>>> out. >>>> >>>> The partial pressure of water vapour above the cloud tops is too low to >>>> convect any signficant latent heat higher >>> >>>You seem to be going to great lengths to repeat my points as though they >>>were your own. I'll take that as a compliment. Once the cloud has >>>condensed, its latent heat has radiated from the cloud tops, >> >> Radiation of the heat (latent or otherwise) does not occur the >> instantly. The air may descend somewhere else before losing all its heat >> to radiation. > >True enough. I misspoke. I should have said the cloud starts radiating >as soon as it begins forming, and continues from that point on. That is true. At this moment what I am in the best mood to add here is that cloud tops near tropopause do not account for most longwave IR radiation from this planet to "outer space". There is even convective cloud formation building to altitudes where cloud tops have low ability to cool by radiation - mostly within ITCZ (intertropical convergence zone), where the updrafts, much of which are part of "global atmospheric circulation" while also "largely confined to ITCZ convection ghotspots", rise to levels so high that their cloud tops are so cold as to either have overshot or else have achieved temperature so low as to experience *warming* by "local radiation balance", including influence of the "upper stratosphere" and the "thermosphere". How things appear to me - the tall/deep convective clouds in/near the ITCZ "largely-establish" the lapse rate from a few or several hundred meters above surface to "ITCZ tropopause level" (lower altitudes have a high rate of achieving lapse rate well short of convection within that latitude-zone during the 18-20 or so hours of each day when within-ITCZ something like 95-97% lacks such tall deep convection). >>> and has a clear shot to space. Above the cloud tops, WV is gone, A few articles ago I did mention 2 points: 1: How radiation-clearshots-to-space or fails to do so varies with wavelength through noted bands. I do consider noted that major GHG abosorption bands with significant ability to both absorb and radiate at "relevant temperatures" has their relevant spectral features of Earth's atmosphere changing by only a small amount if such GHGs have their "atmospheric concentartion" so much as halved or doubled. But keep in mind that over the past few hundred thousand years we have a record of great global temperature fluctuation (10-12 K or so) in response to "Milankovitch Cycles" affecting reception of hugely-much-smaller changes of solar radiation at Arctic and near-Arctic latitudes most-noted-as-around 65 degrees N. >>>radiation is effective, convection isn't needed. >> >> What about when CO2 is present? What about when cloud tops are low? > >There's not much CO2, and when cloud tops are low, temperature is >higher and radiation is greater. When cloud tops are lower, lapse rate is lower. Low cloud tops are mostly where the troposphere has convection limited to a low range of altitude from, the surface (a bit common), otherwise when cloud tops are both low and stratiform. (Cloud tops can easily be a few km below the tropopause.) And the radiation from cloud tops that low mostly runs into GHGs. > It's the integration over the area of >the Earth that counts. A few very effective radiating spots could make a >big difference. Keep in kind that much of that is from: * GHGs in clear air (70% of which exist above the 700 mb level) * Cloud tops so low as to have most GHGs above them, even including water vapor - almost halof of which exists above the 700 mb level >>>>>Â It's in the 10s of kW/m^2 compared to the 500W/m^2 max from >>>>>surface radiation. Â >>>> >>>> It was at the surface, where the partial pressure of water vapour is >>>> around 2300 Pa. The saturation vapour pressure has dropped to 603 Pa >>>> by the time the temperature has dropped to zero Celcius. It drops off >>>> even faster over ice, so it certainly isn't beating radiation at the >>>> effective emitting altitude. >>> >>>Assume at the surface boundary layer we have a thermal with a given >>>humidity and velocity. What do you think happens to a parcel of air, and >>>the energy it contains, as it rises? Keep in mind that matter and >>>energy are conserved. >>> >>>I can tell you, from direct observation, that it continues upward at a >>>relatively constant velocity until it reaches either a change in the >>>lapse rate, or the condensation altitude (cloud base). You need to >>>rethink your position to include that easily verifiable fact. You also >>>need to get out more. Try riding a sailplane in a thermal. >> >> Not that most of the world has thermals from surface to tropopause - >> those are thunderstorms. >> >>>> http://www.engineeringtoolbox.com/water-vapor-saturation-pressure-air-d_689.html >>>> >>>> http://www.answers.com/topic/dewpoint-jpg-1 >>>> >>>> http://faculty.matcmadison.edu/slindstrom/VaporPressure.doc >>> >>>Thanks for the supporting links. I may have posted a couple of them >>>before. >>> >>>>>The lower troposphere is translucent in the 15u band. Â How could >>>>>CO2 play any significant part, compared to radiation? Above the >>>>>clouds, it has a clear shot to >>>>> space. >>>> >>>> CO2 has both 5u and 15u absorbtion bands >> >> I would like to add that the 15 um band is significant at surface >> level temperatures. At 288 K, a blackbody has spectral power >> distribution about 71-72% of peak. > >Sorry, I don't understand what that means. Can you explain? At the 288K temperature that for 1950-1980 or 1930-1980-average that is of Earth''s surface (or atmosphere 4 feet or 2 meters above), thermal radiation at 15 um per-unit-area per-wavelength-unit-bandwidth is 71-72% of the peak for such temperature. >>>Please. Are you now claiming that the surface is radiating >>>significantly in the 5u band? You're the radiation expert, what BB >>>temperature would that represent? My BOE guess is about 300C, which >>>seems a bit unrealistic for Earth, >> >> At 288 K, a blackbody has spectral power distribution about 22% of >> peak at 5 um. There is some surface radiation in that band being >> absorbed by CO2 overhead. > >What percent? It's a fairly narrow band, overlapping water. I would like to say: http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png >Can you explain, using this graph? It looks like less than 5% of the >area under the spectrum to me. > >http://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png That is a wavelength range at which CO2 is much more significant than water vapor despite greater existence of WV than CO2 in this plantet's atmosphere. Also, even in this band (as opposed to the 15-uM-centetred-one) CO2 is a significant greenhouse gas, and at wavelength ranges within this band change of concentration of CO2 changes number of absorptions/re-emissions of thermal radiation at wavelengths in or towards the edges of this band. Though I consider the 15-uM-centered one more significant than the near-5-um-centered one for now. >>> especially at the effective radiation altitude. Looks like you've >>>reached the bottom of the barrel. >>> >>>> http://www.wag.caltech.edu/home/jang/genchem/infrared.htm >>>> >>>> What do you mean by "translucent"? >>> >>>Scattering rather than absorbing, like the frosted glass on a light >>>bulb. I was humoring you. I suspect the lower troposphere is nearly >>>opaque to the 15u band, and satellites are just seeing emission from the >>>top layer. It doesn't matter either way to the argument. Keep in mind that "foggy translucent" by absorbing and re-emitting thermal radiation with all relevent temperatures nearby means that adding GHGs effectively adds a "distrubted layer" (or fraction thereof) of absorption/re-reradiation of longwave IR. That does cause surface to need to have its temperature increase in order to lose heat radiationally to outer space as it did before. (Keep in mind my previous response along the "pinball argument" (my words). >>>> CO2 absorbs and retransmits infra-red radiation at specific lines >>>> within both bands, and this radiation won't have a "clear shot at >>>> space" until it gets high in the stratosphere. >>> >>>How much? And how much difference does it make in view of the negative >>>feedbacks involved in the convective transfer? Try considering the >>>lower troposphere as a variable (temperature sensitive) thermal >>>resistance Thermal resistance has a negative temperature coefficient for convection and a positive one for radiation (due to water vapor increasing with temperature, and secondarily due to percentage of CO2 dissolved in oceans decreasing as sea-level temperature increases). Keep in mind that so little of the world is covered by "deep convection", and close to half lacks clouds at any altitude, that radiation other than from clouds at any altitude (let alone restriction to cloud tops within even 4 km of tropopause) is currently a minority of this planet's "radiation outgo" that balances its "radiation income" from the Sun. >> The majority of the troposphere that is lacking convection has thermal >> resistivity not collapsing until convection occurs. That portion of the >> tropospher has upward mobility in lapse rate. > >Local convection should still be quite effective. Except that in most of the world it does not exist at any layer of the atmosphere having cliuds - close to half the world lacks clouds at any altitude. There is also significant cloud top over this world where the cloud tops are stratiform, and in addition to that a fair amount of the cumuliform (convective-turbulent) cloud tops being in the lower half of the troposphere. >>> and the region above the radiating layer as a relatively smaller, >>>slightly CO2 sensitive resistance. >>> >>>> CO2 is also disproportionately effective at broadening water vapour >>>> absorption lines, and this will be significant in the region close >>>> above the cloud tops where there's still some partial pressure of >>>> gaseous water to absorb and retransmit at water vapour's absorbtion >>>> lines. >>> >>>OK. Now use your radiative transfer model to compare that to the effect >>>of warming (lowering) the emitting layer a few degrees. Don't forget >>>the T^4 term. >> >> Lowering of the emitting layer is what happens if GHGs are reduced. > >Why would GHGs necessarily be involved, since clouds radiate as black >bodies? For one thing, so far a lot of radiation from this planet to outer space to throw back out what it received from the Sun is not from clouds, but from clear air or from the surface. At current atmospheric concentrations of GHGs, there remains wavelengths at which emission at relevant tremperatures is significant and at which the entire atmosphere still has or recently had significant transparency. >> Except the emitting layer will still have the temperature appropriate >> for 1/4 of the solar constant times ratio of solar absorption to >> emissivity of the radiating layer. > >Not if the surface temperature has increased. The lapse rate won't allow >it. The temperature of the emitting layer will increase, radiating the >heat necessary to cool the surface back down - negative feedback. Except that most of the world has room to warm significantly before vertical convection sets in. Especially regions where surface albedo to incoming solar radiation is subject to change as a result of change in radiation balance (specifically change in temperature necessary to maintain such) - Much of the world having snow/ice cover reduced by increase of GHGs can easily warm quite a bit with awfully little increase of local convection from surface or lowest km to so much as 4 km above sea level. And warming of areas so close to the poles will if anything reduce "net global convection" via "global atmospheric circulation" by means of "advection" (which is heat transfer by fluid flow that is, for planets, largely horizontal). >>>Sorry about the repetition, but it was worth it, since you have now >>>apparently caught on to what I was saying. I'm more pragmatic than >>>polite, I guess. Not that I always fail to be rude; I merely do that most of the time and also I "let facts get in the way" most of the time! >> - Don Klipstein (don(a)misty.com) - Don Klipstein (con(a)misty.com)
From: Don Klipstein on 20 Dec 2008 22:01 In article <pan.2008.12.08.08.36.56.199364(a)REMOVETHISix.netcom.com>, Bill Ward wrote: >On Mon, 08 Dec 2008 03:54:11 +0000, Don Klipstein wrote: Oh so long ago, boy-oh-boy am I so slowed down this time of this year, majority of 2 weeks! >> In <pan.2008.11.29.05.43.32.198332(a)REMOVETHISix.netcom.com>, Bill Ward >> wrote in part: >> >>>On Fri, 28 Nov 2008 19:25:22 -0800, bill.sloman wrote: >>> >>>> On 27 nov, 20:50, Bill Ward <bw...(a)REMOVETHISix.netcom.com> wrote: >>>>> On Thu, 27 Nov 2008 07:50:47 -0800, bill.sloman wrote: >>>>> > On 27 nov, 06:32, Bill Ward <bw...(a)REMOVETHISix.netcom.com> wrote: >>>>> >>>>> > <snip> >>>>> >>>>> >> As you put it up thread, "the stratosphere isn't functioning as an >>>>> >> insulator." >>>>> >>>>> >> If the stratosphere is transparent, and there is an excess of >>>>> >> convective capacity in the troposphere (driven by the lapse rate), >>>>> >> how can trace amounts of CO2 affect surface temperatures? If >>>>> >> convection is sufficient to get latent heat to the tropopause, >>>>> >> where it can radiate from cloud tops, etc, it has a clear shot at >>>>> >> 3K deep space. The tropopause is there because it represents the >>>>> >> top of the convective mixing layer. Because of increasing UV >>>>> >> heating, the stratosphere has an inverted lapse rate, which >>>>> >> prevents convection. >>>>> >>>>> > You seem to have set up a straw man by claiming that you can slice >>>>> > the atmosphere into three layers - >>>>> >>>>> > - the troposphere where heat transfer is only by convection >>>>> >>>>> > - a very thin tropopause which does all the radiation >>>>> >>>>> > - the stratosphere which does nothing >>>>> >>>>> > which - unsurprisingly - leads you to incorrectly conclude that CO2 >>>>> > cann't do anything. >>>>> >>>>> Where did I say the radiation all comes from a thin layer? You must >>>>> be misinterpreting the concept of effective radiating altitude. >>>> >>>> I very much doubt it. The proposition that the you think that all the >>>> radiation comes from a thin layar at the tropopause folows direcly from >>>> your claim that radiation doesn't play a significant role anywhere in >>>> the troposphere, which strikes me as implausible. >>> >>>Below the effective radiating layer (cloud tops) radiation is swamped by >>>convection, so CO2 can have little effect. >> >> What about in the majority of the troposphere lacking convection? And >> how are cloud tops the effective radiating layer in the half of the world >> that lacks clouds? > >It doesn't have to be everywhere, just in the places where most of the >cooling takes place, such as the tropics. For one thing, most radiative cooling of this world to balance radiative warming from the Sun is mostly not from cloud tops anywhere near trhe tropopause, I might dare say mostly from where this planet lacks clouds at any altitude. The tall deep convective clouds in the ITCZ ("Inter-Tropical Convergence Zone" rise so tall there with assistance by "global atmospheruic circulation" - with suitably-weighted-average over relevant altitudes of the atmosphere it is warmer in the tropics than towards the polses, so in ITCZ the atmosphere generally rises and towards the polses the atmosphere generally sinks. We achieve a "heat engine" here - namely one of "global atmospheric circulation" notably achieving the cold-spots-at-top-level-troposphere of tropical air rising where it does on-average gets even-colder than most of this planet's atmosphere elsewhere. Such a model works due to most despite not all levels of the atmosphere involved in "global circulation" being warmer towards the equator and colder towards the poles. Air rising in "tropical deep convection hotspots" is assisted in its rising to altitudes so high that it cools to temperatures so cold that on worldwide annyual average, in the ITCZ is where air that high is so cold (-60 to -75 C or whatever). Keep in mind that most of the tropics are clear and most cloud tops are elsewhere in the world and both lower and warmer - despite "global atmospheric circulation" having a very significant part through the small minority of the tropics covered by tall deep thunderheads within/near the ITCZ. >>> Above the radiating layer, there's not much CO2 left, Based on my latest calculations as to oversimplification as to what that altitude is (350 mb level, roughly 7.6-8 km above sea level give-or-take), 35% of all GHGs other than water vapor are above this level. A smaller percentage of this planet's atmospheric WV is above this level. As for what "pressure level" is 50-50 - the "500 mb level" is close enough for all GHGs other than WV, and the "700 mb level" is close enough for WV - that one is noted as having great positive correlation between "vertical velocity" and "precipitation production" ("my words"). >> Assuming Earth reflects half of solar radiation and has .95 emissivity >> of low temperature thermal IR (the figure on my non contact >> thermometer), Earth radiation achieve radiation balance at 237-238 K. (I >> may have posted a few degrees lower before by forgetting the .95 >> figure). 237 K is about -36 C. >> >> 237 K is when 95% of blackbody radiation intensity is 1/8 of the solar >> constant. >> >> Average location of a photon radiated from Earth to outer space is >> where >> temp. is -36 C, but that is give-or-take a lot, since a lot of thermal >> radiation can go some fair distance through the atmosphere before being >> absorbed. >> >> On average, the altitude at which temperature is 237 K is around the >> 300 >> mb level, which has about 30% of the mass of the atmosphere above it. >> However, a lot of photons radiated to space from Earth come from >> greatly >> different altitudes, some of which have more than 30% of the atmosphere >> overhead. >> >>> and the 15u band is off peak, >> >> Peak wavelength of a blackbody at 237 K is around 12.5 um. At 15 um, >> radiation is about 91% of that at peak wavelength. > >You are 18K lower than another similar analysis: > >http://www.atmos.washington.edu/2001Q1/211/notes_for_011001_lecture.html > ><begin excerpt> I run low in time for this evening after this evening's load of beers, but I do so far mention that your most-immediate-above cite mentions a figure of 30% of solar radiation reflected, while I have been working on 50%-reflected. The above link says solar constant is 1368 watts per square meter. (I was working previously on 1366.) 70% of that times 1/4 is 239.4 watts per square meter, with blackbody radiating that at indeed 255 K to nearest degree or even half a degree probably. So far for this evening, I would say that "standard atmosphere" of this planet is 288 K at the surface and cooling at close to the "1-size-fits-all-wet-adiabatic-lapse-rate" until hitting tropopause, which at this rate would be 255 K or a bit over 5 km from surface or hardly at all below 500 mb level. Keep in mind that albedo of our planet to solar radiation appears to me to be currently closer to 50% than to 30%, due in part to slight reflectivity of water surface, maybe due in slight part to reflectivity of low clouds and land, and also appearing to me to be due to significant (though also minority) reflectivity of snow and ice cover - some of which goes away if the surface and/or lower troposphere is warmed by increase of GHGs (or anything else). - Don Klipstein (don(a)misty.com)
From: Don Klipstein on 21 Dec 2008 20:44 In article <pan.2008.12.20.06.41.07.173163(a)REMOVETHISix.netcom.com>, Bill Ward wrote in part: >On Sat, 20 Dec 2008 04:52:58 +0000, Don Klipstein wrote: > >> In article <pan.2008.12.08.09.21.16.182224(a)REMOVETHISix.netcom.com>, Bill >> Ward wrote: >>>On Mon, 08 Dec 2008 04:30:44 +0000, Don Klipstein wrote: >>>> You can slow down the upward transfer by radiation by adding more >>>> stops in the radiative path, by adding GHGs. >>> >>>EM travels at c. IR can be converted to sensible heat, but it can't be >>>slowed. >> >> Suppose the surface is at 288 K and radiating to some target layer at >> 225 K. >> >> Surface is radiating 39 mW/cm^2 and receiving 14.5 mW/cm^2. Net >> radiative heat transfer is 24.5 mW/cm^2. >> >> Now, add some layer in between that absorbs and reradiates everything. >> >> That intermediate layer then has to be at 288 K to transfer 24.5 mW/cm^2 >> to the top layer - and is as a net receiving 24.5 mW/cm^2 from the >> surface. >> >> That intermediate layer is radiating 39 mW/cm^2 to the surface, so the >> surface has to be radiating 63.5 mW/cm^2 in order to achieve net upward >> radiative heat transfer of 24.5 mW/cm^2. A blackbody needs to be at 325 >> K to transfer 24.5 mW/cm^2 to the 225 K outer layer with an >> absorbing/reradiating layer in between. > >That seems to assume the active layers are somehow fixed in place. If >they are gases, they will warm as they absorb IR, become less dense and >convect. They don't convect until the lapse rate increases to the adiabatic lapse rate. In most of the troposphere, the lapse rate is short of adiabatic. > Another way to look at it is to assume the optically dense gas >layer is simply heated by surface IR, maintaining radiative equilibrium >with the surface at the lower skin, then moves the heat through the layer >by conduction and convection to the top skin, which is in turn in >radiative equilibrium with the upper target. The atmosphere is optically thin enough to most thermal IR that it is absorbed and re-emitted no more than a few times. And much of the world has its surface cooled by radiation with no convection overhead. >I see no reason to assume that IR is carrying heat through an optically >dense gas. Conduction and convection seem to work quite adequately in >humid air except when the climate somehow becomes involved. How does the >gas know whether it should be internally carrying heat by conduction or >radiation? Isn't the result the same? > >It seems much less complicated to assume the layers are simply hot gas, >and will transfer heat internally just as gases do in all other >disciplines, with radiative transfer only as needed through any >radiatively inactive regions (which will still convect and conduct). > >Heat will eventually tend to rise through the troposphere, whether by >radiation or convection. If IR is absorbed in the gas, the resulting hot >spot will rise via density differences. I don't see any other choice. If IR is absorbed by the atmosphere worldwide, that does not make a localized hotspot to rise. >All gases have thermal conductivity, independent of radiative transfer. Air has thermal conductivity low enough for air to be as much as 2 degrees C warmer 1.5 meters above the ground than the ground is on a clear calm night. It sure appears to me that the heat escaping the surface has to escape nearly enough entirely by convection and radiation. >>>Is it at 255K? That seems to be the usual figure. >> >> I was figuring lower - Earth is receiving solar radiation at a rate >> per >> unit surface area of about 1/8 the solar constant. Cross section is pi >> times radius squared, surface area is 4 times that, and albedo is about >> 50%. Blackbody radiates 1/8 of 1366 watts/m^2 at about 234 K. >> If low temperature emissivity of Earth as a whole is the .95 that >> instructional material for my non-contact thermometer says is close >> enough to ("my words") "1-size-fits-all" for nonmetallic materials, make >> that "effective radiating temperature" 237 K. > >Those are probably different initial assumptions than the other >calculation used. If it is 255 K rather than 237 K, that would mean the Earth absorbs 67% of solar radiation. However, that may be erroneously oversimplified because the radiation comes from places that are not all at the same temperature. >>>> More CO2 means the lower troposphere gets more opaque in the 15 um >>>> band. >>> >>>Which makes convection more effective by converting IR to hot air. >> >> Or which makes the surface or lower atmosphere warmer than otherwise >> when those can warm up by some amount without achieving convection. >> That's most of the world at night and a fair amount of daylit area >> outside the tropics. > >Yes. Places where there's relatively less cooling taking place. But still significant cooling. In another article I posted a link to a global map of insolation, after effects of atmosphere and clouds. The polar regions have to get rid of something like 100 watts per square meter, plus heat advected to them from warmer parts of the world. >>>>> Above the clouds, it has a clear shot to space. >>>> >>>> What about where the tops of the highest clouds are below the 700 mb >>>> level? What about in the clear half of the world? >>> >>>It doesn't have to be everywhere to be an effective mechanism. >> >> It has a significant effect, but significant radiation comes from >> clear >> air and from ground. The ground does cool easily at night when there >> are no clouds overhead and when there is no convection. > >But the surface is colder, so the T^4 factor kicks in. If the surface cools by 15 K out of 290 from midafternoon to dawn, T^4 decreases by 19%. >>>> around 150-210 nm or somthing like that. That's why the upper half >>>> (or 2/3 or whatever) of the stratosphere has an inverted lapse rate. >>> >>>Which means it should be hotter and radiate more. >> >> It's hotter, but radiates less easily than the more-GHG-dense >> atmosphere >> underneath. It is indeed cooled by radiation. This is mainly above the >> altitude of the equatorial tropopause - which is around the 110-120 mb >> level, above 88-89% of GHGs other than water vapor and above a much >> higher percentage of water vapor. >> >> Between the stratosphere and the thermosphere is the mesosphere, with >> lapse rate in the direction of getting colder with increasing altitude. >> Apparently GHG radiating ability decreases less than absorption of solar >> UV does as altitude increases through that layer, though both figures >> are very low. >> >>>> CO2's 15 um band plays a significant role from the lower >>>> stratosphere >>>> through the lower troposphere. >>> >>>I'm still not convinced of that. >> >> A blackbody radiator at relevant temperatures (220-320 K) has >> radiation at least 60% of that of peak wavelength at 15 um. > >And CO2 is not a blackbody radiator. Looking at the wiki graph link, I'd >guess that the 15u band could absorb only about 25% of the 310K blackbody >radiation, and less, if Sloman was correct about the fine band structure >leaving holes. It probably is less - but absorbing 20 or 15% of the thermal radiation surely appears significant to me. The Wiki article on greenhouse gases says that CO2 accounts for anywhere from 9 to 26% of atmosphere GHG effect. - Don Klipstein (don(a)misty.com)
From: Don Klipstein on 21 Dec 2008 21:11
In article <pan.2008.12.15.07.25.04.110636(a)REMOVETHISix.netcom.com>, Bill Ward wrote in part: >On Mon, 15 Dec 2008 03:49:54 +0000, Don Klipstein wrote: > >> In article <pan.2008.12.02.09.04.49.526817(a)REMOVETHISix.netcom.com>, Bill >> Ward wrote: >>>On Tue, 02 Dec 2008 05:55:11 +0000, Don Klipstein wrote: >>> >>>> In <pan.2008.11.26.21.17.23.310423(a)REMOVETHISix.netcom.com>, Bill Ward >>>> wrote: >>> >>>Do you think that the "wet adiabatic" environmental lapse rate is related >>>to latent heat, or is it simply less than the dry adiabatic lapse rate >>>because it's not at equilibrium? >> >> It is less due to latent heat. >> >> The "1 size fits all figures" that I have heard are 3.5 degrees F per >> 1,000 feet for the wet one and 5.4 degrees F per 1,000 feet for the dry >> one. >> >>>>> Is it primarily by radiative transfer, or convection? It seems to >>>>> me >>>>>it must be convective, simply because warm, wet air is less dense than >>>>>cold, dry air, and quickly rises to maintain the lapse rate. >>>> >>>> Much of the time the answer is a significant factor other than >>>> radiation and vertical convection. Much of the "global convection" >>>> involves air movement within a degree of horizontal, and often forming >>>> clouds when moving upwards. Sometimes the lapse rate there is between >>>> the "dry adiabatic" and the "wet adiabatic" rates and the clouds have >>>> billowy cumuliform tops or are cumuliform throughout. Sometimes "warm >>>> advection" occurs more at cloud-top level than at cloud-base level >>>> (from the windspeed being greater higher up in the troposphere), >>>> causing the clouds to be stratiform. >>> >>>OK, that all sounds plausible, but I'm not sure how much effect the >>>horizontal component would have, other than the obvious mixing. >> >> The horizontal component involves atmospheric heat transfer from the >> tropics to the poles. It is very significant. It leads to frontal >> inversions, which cover significant area ahead of warm fronts (including >> areas where the warm fronts fail to reach at the surface). It leads to >> existence of stratosphere at middle and upper latitudes at pressure levels >> below that of the tropical tropopause. >> >>>>>IR radiated from the surface would be quickly absorbed by WV, clouds, >>>>>CO2, and other GHGs, and at 500W/m^2 would be overwhelmed by the 10's >>>>>of kW/m^2 available from convection of latent heat. >>>> >>>> Half the Earth's surface has no clouds overhead at any altitude. >>> >>>Surely you mean "at any given time". Or are there really regions >>>comprising half the Earth's surface that have never had a cloud in the >>>sky? >> >> I did mean "at any given time", and "those given times" in "those >> given locations" account for half the world lacking clouds at any >> altitude. > >OK, I'll buy that as an average. But I'll bet the tropics are far more >likely to be cloudy than the polar regions, and that's where most of the >cooling occurs. > >>>> The surface manages to radiate *somewhat* to outer space at night when >>>> the air overhead is clear - otherwise there would be no such thing as >>>> nighttime frost when air 2 meters above the surface is at +2 degrees C >>>> (a fairly common situation). Some of the outgoing radiation can easily >>>> be absorbed and reradiated a couple or a few times by GHGs, but net of >>>> that is upward (and upward net is reduced by increase of GHGs). >>> >>>OK, no argument with that. I look at it as the surface radiating to a >>>target warmer than 3K space, but it's the same math. >>>> >>>>>At night, convection stops, but cooling is not required at night. >>>>>Convection kicks in during the day, when cooling is needed. >>>> >>>> Cooling still occurs at night by radiation. 5 AM temperature has a >>>> great rate of being less than 10 PM temperature. Upper level of >>>> radiation by atmosphere at night has half of its radiation to outer >>>> space. That heat comes from radiation from surface - even if absorbed >>>> and reradiated a couple times along the way. >>> >>>Agreed. At night the flux is always outward. >>> >>>> The "upper radiation level" also varies greatly with wavelength. >>> >>>Do you mean the "effective radiating altitude", which is calculated, or >>>some sort of integrated spectrum involving all the photons reaching a >>>surface outside the atmosphere, like a satellite imager? Neither I, nor >>>apparently Google, is familiar withe the term "upper radiation level". >> >> Looks like I did not choose wrds well - it should have been "effective >> radiating altitude". >> >> Keep in mind that the "effective radiating altitude" is very fuzzy, >> since some wavelengths radiated by the surface have good atmospheric >> transparency (and a fairly clear shot to space) as long as there are no >> clouds, others have low chance of reaching the 500 mb level without being >> absorbed, and some are in-between - with absorption and reradiation >> varying directly with concentration of GHGs. > >That's my point. It's not well enough known to claim 1.5W/m^2 is going to >make any difference at all. All it takes is a minor negative >feedback loop to correct for that small an effect. The Ice Ages having temperature swinging 10-plus K from slight periodic changes in insolation show that we have a lot of positive feedback. >>>>>I don't see how radiative cooling is even necessary below the cloud >>>>>tops, since there's plenty of cooling capacity from convection. >>>> >>>> When frost or dew forms on the ground and on cars and trucks, the >>>> heat >>>> loss has a very impressive rate of by being by radiation. >>> >>>True, but radiation is peanuts compared to the available cooling >>>capacity of latent heat during the day. If the surface radiation were >>>blocked, convection could easily make it up. >> >> What about on days when there is no convection past the 750 mb or so >> level for even a minute? (I see plenty of those even with sky >> half-clear and cumulus clouds present.) What about in Arctic and >> upper-midlatitude areas where change in radiation balance during the 18 >> or whatever hours per day with little convection has a significicant >> effect on snow/ice cover, and that affects how much solar radiation the >> surface absorbs? > >It's the total transferred power that counts. It doesn't take much latent >heat convection to make up for a lot of radiation. The place to look for >changes is where the cooling is greatest, not places which are already >being warmed by the tropics. Cooling is significant in the polar areas. The global insolation map in the Wiki article on insolation shows the polar areas getting about 1/3 as much insolation as the tropics do. Cooling is even more than 1/3 that of the tropics, since global circulation transfers heat from the tropics to the polar regions. Where the surface can warm significantly before convection occurs is probably where the world can warm more if GHGs increase. I would also expect more warming in areas where warming reduces surface albedo. >>>>>Once the energy reaches the tropopause, as you imply, it's a pretty >>>>>straight shot to 3K deep space, since there's not much atmosphere left >>>>>to absorb IR. >>>>> >>>>>Perhaps it's easier to see if you look at the lapse rate as bounded at >>>>>the top by the effective radiating temperature, and consider the >>>>>surface temperatures as derived from that and the adiabatic lapse >>>>>rate. >>>> >>>> That gets complicated by half the troposphere having lack of clouds >>>> at >>>> any altitude, and there are separate adiabatic lapse rates for clear >>>> air and clouded air. The global atmospheric average is close to the >>>> "wet" one, leaving upward mobility of lapse rate in the clear half of >>>> the world and in clear layers of the atmosphere in the clouded half of >>>> the world. >>> >>>At any given point, the applicable lapse rate should be obvious, >>>depending on whether cloud is present. I'm not convinced the lower >>>"average" environmental lapse rate has much to do with latent heat. It >>>might just be off-equilibrium due to transport lags or the like. >> >> It just happens to be that the "average lapse rate below the >> tropopause" is close to the wet adiabatic one. Close to the equator, >> it is more than coincidental - global circulation (from atmosphere >> below_tropical_tropopause_pressure_level as-a-whole) being warmer >> towards the equator and cooler towards the poles has air in the >> intertropical convergence zone rising. That largely establishes the >> lapse rate in the ITCZ as being close to the wet adiabatic one from >> the levels of the bases of the deep tall tropical convective clouds to >> the tropical tropopauuse. Below that cloud base level where those >> clouds form, the lapse rate is close to the dry adiabatic one at hot >> times of the day, and less at other times. >> >> Although it sounds like global circulation merely forces upward air >> movement in the ITCZ and that should cause clouds other than the billowy >> cumulus of natural convection, those show up anyway (along with a lot of >> clear air). Surface temperature in the ITCZ is not uniform. For one >> thing, some parts of the ITCZ have daylight and others have night. Also, >> ocean currents cool the ITCZ unevenly. So, upward air movement in the >> ITCZ occurs in hotspots where natural convection is sufficient to >> account for the upward global atmospheric circulation in the ITCZ - and >> the clouds there are billowy thunderheads, with many having anvil tops. > >I've often seen precipitation falling out of the anvil, many times never >reaching the ground. The energy in a thunderstorm is staggering, and >seems far more than IR could ever provide. Most of that energy had >to have come from the surface, and there's really no way back down. It >seems to me it has to radiate to space. Little of the surface is covered by thunderheads. And the atmosphere at the level of tropical anviltops is so cold, that it actually experiences slight warming from radiation. The air eventually does cool by radiation where it descends. >Thermals are what got me started on this issue. I asked myself just how >much IR it would take to lift a sailplane at a thousand feet/minute. >I immediately had doubts that IR is significant. The energy is clearly >mechanical energy of convection, and the cloud (if any)sitting on top of >the thermal has to represent an order of magnitude more energy from >latent heat. > >Thermals may not be all that common on the average, but when they do >occur, they must carry orders of magnitude more energy than IR. > >When I look (longingly) at pictures of tropical islands, I see very >familiar looking clouds. I have to assume the dynamics are similar, >and that they are common in the tropics. So I need a lot of convincing >evidence before I'll believe their heat transfer ability is somehow >comparable to an already cold polar surface or similar situation. All it >would take is a slight modulation of humidity or lapse rate to have large >effects on the power transmitted, far greater than the 1.5W/m^2 CO2 >forcing assumed in the climate models. I agree that tropical thunderstorms lift warm air accounting for thermal power densities many times the solar constant. However, that heat is mostly not radiated at the tropical tropopause - the anviltops are at about the same temperature as the surrounding clear air at the same altitude, and it is actually colder at that altitude in the tropics than in the middle latitudes. Cooling of the tropics is ultimately mostly from radiation from altitudes lower than the tropical tropopause and from global circulation. >> Do keep in mind that there is global atmospheric circulation at >> altitudes and pressure levels that are troposphere in the tropics and >> stratosphere elsewhere. Air rising through the ITCZ to close to the 100 >> mb level does not all go down there but some descends elsewhere >> poleward. And a lot of that moves poleward at altitudes where the is >> little hope of convection to such level from the surface, due to surface >> being cooler than in the ITCZ. At some of these >> extratropical-stratospheric altitudes and pressure levels, atmosphere is >> even usually warmer than it is over the ITCZ because over the ITCZ it is >> so cold (from cooling by uplifting) that local radiation balance warms >> the air moving largely horizontally at/near the tropical tropopause >> level. It cools by radiation in order to descend elsewhere, with much >> of that done during the descent - especially in the polar regions. > >That seems reasonable, but I don't see how it really affects the tropical >convection cells. That's how the energy got up there in the first place. I don't think radiation does much to tropical convection cells. But if the polar regions warm with increase in reception of solar radiation, then horizontal temperature gradient will decrease. That will slow global circulation, which means slightly less cooling of the tropics. The tropics will warm slightly as a result, and the thunderstorms would have to become a little more intense. - Don Klipstein (don(a)misty.com) |