tag:blogger.com,1999:blog-7729093380675162051.post8979707845177499962..comments2024-03-28T13:56:47.604+11:00Comments on moyhu: Calculating the environmental lapse rateNick Stokeshttp://www.blogger.com/profile/06377413236983002873noreply@blogger.comBlogger63125tag:blogger.com,1999:blog-7729093380675162051.post-85627750469422951962016-10-13T17:41:08.869+11:002016-10-13T17:41:08.869+11:00Sorry, I'm having trouble understanding the qu...Sorry, I'm having trouble understanding the question. The total air mass doesn't vary much (just a little with humidity). The rest I can't really understand.<br />Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-18787302562996548942016-10-11T20:15:33.974+11:002016-10-11T20:15:33.974+11:00How does this relate to air mass variation or real...How does this relate to air mass variation or real time application in physical contexts other than paelogeographic and atmospheric structured arguments? Is there a unique and qualitative attribute with the parrametrics of a specific feature?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-48657047227383279312014-11-04T09:41:18.509+11:002014-11-04T09:41:18.509+11:00Hey, I tinkered with the blog javascript and I thi...Hey, I tinkered with the blog javascript and I think I found a bug. The comment window should now be adjustable. I'll see what else I can fix.Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-21135244050169343422014-11-04T05:00:27.268+11:002014-11-04T05:00:27.268+11:00Err, 'stability criterion'Err, 'stability criterion'Steve Fitzpatricknoreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-23097064603215568522014-11-04T04:58:43.372+11:002014-11-04T04:58:43.372+11:00As I mentioned to Steve, I do lose comments someti...As I mentioned to Steve, I do lose comments sometimes. This happens even when I am logged into my google account.<br /><br />The only work around I've found is to press the preview button before the submit button.<br /><br />0n my browser the preview window is virtually useless, except for very short comments—this is not a complaint, it's just why I wouldn't automatically preview my comments.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-85762343229006168052014-11-04T04:57:43.344+11:002014-11-04T04:57:43.344+11:00Nick,
Here is what I tried to post earlier:
I th...Nick,<br /><br />Here is what I tried to post earlier:<br /><br />I think Carrick's graph (day and night lapse rate profiles) is very informative. The daytime curve shows that the actual lapse rate is higher than the DALR, especially below ~1 Km, which makes perfect sense to me. The DALR is a stability criteria, and there can only be active convection when the DALR is exceeded. At or below the DALR the column is stable and any mixing can only take place due to horizontal shear driven turbulence. Upward heat transfer is going on both by convection and radiation, with radiation becoming relatively more important at higher altitudes, until near the tropopause the lapse rate falls below the DALR and convection stops. Higher absolute humidity in the air (but below saturation) reduces the relative importance of radiative flux at all altitudes, and so increases the relative importance of convection. In a simplified system where there is no horizontal wind shear, the size of the discrepancy between the actual lapse rate and the DALR should dictate how much convective transfer there is, and at higher humidity this discrepancy should increase all along the air column, indicating the increased importance of convection.<br /><br />Carrick's night time curve shows that the lower troposphere becomes stable (lapse rate below the DALR), where absent shear driven turbulence only radiative transfer is important. Wind shear driven turbulent mixing, opposing a stable lapse rate (that is, below the DALR), serves to transport heat from above to below because of adiabatic heating. <br /><br />When you add enough moisture to get condensation, there must be a two-tier lapse rate: low altitude where the DALR governs convective stability, and a higher altitude above which the MALR governs convective stability. Seems to me no simple model of this very complicated process is likely to do a reasonable job, especially when the influence of wind shear and cloud formation is included. Steve Fitzpatricknoreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-31835893393992214312014-11-04T03:55:39.053+11:002014-11-04T03:55:39.053+11:00Nick, I think it's the case that daytime lapse...Nick, I think it's the case that daytime lapse rates at the top of the ABL tend to look nearly adiabatic.<br /><br />I believe point of the radiation equilibrium lapse rate being larger than the DALR near the surface, is that it implies radiative transfer will force the daytime lapse rate to be close to the DALR stability limit. So the DALR is a good zeroth order approximation to the lapse rate you will observe in the upper layer of the daytime convectively dominated ABL.<br /><br />The other important thing to see is that the DALR isn't a prediction of the observed lapse rate, rather it's an important "speed limit" on the maximum rate at which temperature can vary vertically in the atmosphere. So while it's useful for the specific application of the ABL, it has little to do with the actual observed lapse rate in the free atmosphere layer above the cloud interaction layer, other than being a not very interesting upper bound on the ELR.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-56516072942301716532014-11-04T03:15:37.125+11:002014-11-04T03:15:37.125+11:00Steve,
Sorry about that problem. I don't know...Steve,<br /> Sorry about that problem. I don't know what is happening. There is nothing in the spam bin (which is itself unusual). AFAICS, every comment of yours that I have email notification of has appeared.<br /> <br /> I invoke captcha during quiet commenting periods, but not in recent days.<br /> <br /> I have found acquiring a Google ID helpful. My wordpress ID was also good, but recently problematic. The google ID means you don't have to enter anything, and it used to mean slightly better privileges, like being able to paste into comments.<br /> Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-75743013532015185512014-11-04T02:40:49.370+11:002014-11-04T02:40:49.370+11:00Steve, this happens to me too… what I found works ...Steve, this happens to me too… what I found works is to always press the preview button. I also write my comment in an editor then copy and paste it in, which helps reduce the chance of lost data (at the risk of copy and paste errors).Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-12768915100004838962014-11-04T01:43:45.898+11:002014-11-04T01:43:45.898+11:00Nick,
I am puzzled. Sometimes I try to make a com...Nick,<br />I am puzzled. Sometimes I try to make a comment and the 'capcha' (sp?) window pops up, and the comment shows up. Sometimes the 'capcha' window does NOT pop up, my comment disappears, and is lost forever (happened twice this AM, once yesterday). Does blogger not play well with certain browsers?Steve Fitzpatricknoreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-71692440384834249562014-11-03T19:50:48.919+11:002014-11-03T19:50:48.919+11:00Carrick,
I've realised I made a substantial e...Carrick,<br /> I've realised I made a substantial error here. I assumed entropy balance as if the air were adiabatic. But as you say, there is a significant radiative flux interacting with the air, and that carries entropy with it. So it isn't the case that the heat pump has to completely counter the entropy creation.<br /> <br /> I'm not sure what to make of your plots showing a radiative flux much greater than the gradient would imply. They say that convection transfers heat up to straighten the gradient to the LR. The logic of my corrected equation agrees. But the LR is generally in the convectively stable region. Maybe transient instability is enough.<br /> Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-21726840920062883212014-11-03T14:58:08.033+11:002014-11-03T14:58:08.033+11:00Regarding relative magnitudes of radiative vs conv...Regarding relative magnitudes of radiative vs convective equilibrium, one of the standard papers that discusses this is:<br /><br />http://www.clidyn.ethz.ch/ese101/Papers/manabe67.pdf<br /><br />See Figure 5.<br />Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-448901287264519902014-11-03T12:24:10.047+11:002014-11-03T12:24:10.047+11:00By the way, I'm pretty sure you're correct...By the way, I'm pretty sure you're correct about there being cloud condensation above 2500 m.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-11719379945157298472014-11-03T11:42:23.348+11:002014-11-03T11:42:23.348+11:00Nick: It's not obvious to me that the radiativ...Nick: <i>It's not obvious to me that the radiative equilibrium gradient is larger than the DALR. If it were, then there would have to be a very effective counter-pump. </i><br /><br />Actually, that is typically the case near the surface, so it does act to drive convection:<br /><br />https://dl.dropboxusercontent.com/u/4520911/Climate/Temperature/RadiativeVsConvective.pngCarrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-25537326977247893672014-11-03T11:26:39.326+11:002014-11-03T11:26:39.326+11:00Carrick,
My interpretation of the Albuquerque dat...Carrick,<br /> My interpretation of the Albuquerque data is that there is a diurnal transient near the ground, which fades with altitude. Around 1000 m, there is plenty of wind energy, so good heat pump. Looks like at 2500 m, maybe cloud condensation?<br /> Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-40303906502099856002014-11-03T10:54:43.562+11:002014-11-03T10:54:43.562+11:00Steve, I agree, as long as you have strong convect...Steve, I agree, as long as you have strong convection --driven circulation, you'd expect to see a lapse rate close to DALR.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-33289752101182647362014-11-03T10:28:38.254+11:002014-11-03T10:28:38.254+11:00This diagram maybe helps explain it:
http://1.bp....This diagram maybe helps explain it:<br /><br />http://1.bp.blogspot.com/_QVNrX4AKZAY/TPhVbPeyfLI/AAAAAAAAFAs/larwRX5QQEU/s1600/bl_evol.jpg<br /><br />Here's data from Albuquerque (nearly optimal conditions to show the effect, which is atypical for Albuquerque, due to mountain generated winds):<br /><br />https://dl.dropboxusercontent.com/u/4520911/Climate/Temperature/ABQ20140414.pdf<br /><br />Red curve is 5 PM MDT and blue curve is 5 AM MDT. Note that between 1000-2000 meters elevation, the ELR is very close to DALR, with the nocturnal lapse rate in the residual layer actual actually closer to DALR than the daytime convective layer is.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-52701801878360012172014-11-03T10:10:31.095+11:002014-11-03T10:10:31.095+11:00Nick, to be clear I was referring to the lapse rat...Nick, to be clear I was referring to the lapse rate in the residual layer, not the surface boundary layer (where the nocturnal lapse rate is typically negative).Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-85777167634329189422014-11-03T10:06:29.850+11:002014-11-03T10:06:29.850+11:00Pekka, to be clear, what I was arguing is that for...Pekka, to be clear, what I was arguing is that forced convection in the ABL is responsible for the ELR approaching the DALR during typical daytime conditions.<br /><br />The issue with the residual layer, is it is a layer of air that becomes "detached" from the surface after the establishment of a nocturnal (stable) boundary layer. When it is not disturbed (typically this is between sunset and roughly sunset + 4 hours), what you see is a further steeping of the lapse rate.<br /><br />In the daytime surface layer (roughly the first 100-m), the lapse rate typically exceeds the DALR, but again this is generally due to convective forcing, and there is a lot of low-altitude turbulence associated with it.<br />Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-49827814323375782362014-11-03T09:43:08.338+11:002014-11-03T09:43:08.338+11:00Carrick,
Ignoring nocturnal boundary layer influe...Carrick,<br /><br />Ignoring nocturnal boundary layer influence, it seems to me that below the altitude where clouds will form, the DALR pretty much has to be the dominant lapse rate. I mean, the DALR should apply up to where moisture starts to condense, then a lower moist lapse rate should apply... at least until some higher altitude (with lower temperature) where there just isn't enough remaining water vapor in the air to give much more latent heat. <br /><br />When I fly during the day (which is, unfortunately, too often), I often see a very clear altitude where clouds begin to form, representing the temperature where air rising air from the surface becomes saturated. 'Puffy clouds' form at this level, reflecting much solar radiation (and for sure absorbing a fair amount of solar infrared!) thus cooling the surface. But most of the time these clouds dissipate without producing any rain. The air above seems to be often dry enough that collectively formed clouds evaporate rather than generate rain. But they for sure reduce solar flux at the surface. Of course, when the sun sets, the convection and cloud formation usually stops, and the sky clears.Steve Fitzpatricknoreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-81676495262274235132014-11-03T09:20:17.964+11:002014-11-03T09:20:17.964+11:00Steve,
I include the IR effect of humidity in the...Steve,<br /> I include the IR effect of humidity in the conductivity k. It doesn't determine the lapse rate directly, but affects the amount of work that the heat pump has to do to counter leakage. Since more GHG means less conductivity, that actually reduces the loss and shifts LR toward DALR.<br /> <br /> The effect of condensation, OTOH, is effectively a boost to c_p, and brings down the "D"ALR directly.<br /> Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-47059273586310024352014-11-03T09:15:30.324+11:002014-11-03T09:15:30.324+11:00Carrick (and Pekka),
I found this data interestin...Carrick (and Pekka),<br /><br />I found this data interesting: http://www.ncdc.noaa.gov/cdo-web/datatools/records<br /><br />Note that the over the past year, there were lots of low maximum records set (no doubt reflecting unusually cold weather in the mid-west of the USA in the past winter), but far fewer low minimum records. Note also that while there were relatively fewer high maximum records set, there were many more high *minimum* records set. The early morning hours appear warmer than in the past. <br /><br />Which suggest to me that underlying GHG driven warming trend is more manifest in in the minimum temperature than in the maximum temperature, consistent with a stronger influence of higher GHG's (including water vapor) on the temperature of the nocturnal boundary layer, and weaker influence on daytime temperature, where convection is driven by solar heating. (Except at high latitudes in winter, where an inversion may be stable during the day due to very weak solar heating.)<br /><br />Boundary layer effects seem to me a good explanation for some divergence of satellite lower tropospheric temperature trends from surface temperature trends.<br />Steve Fitzpatricknoreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-84022866985022942122014-11-03T09:04:11.983+11:002014-11-03T09:04:11.983+11:00Carrick,
"It's worth reiterating that th...Carrick,<br /> <i>"It's worth reiterating that the dry adiabatic lapse rate (DALR) is a condition for stability, it's not actually a predicted lapse rate."</i><br /> <br /> My contention in these posts is that there is a mechanism that drives toward the DALR. It's not just a stability criterion. Vertical motion in a sub-DALR lapse pumps heat downward, building up the gradient. Or allowing the gradient to exceed the Fourier law value. In this post I've tried to predict the lapse rate. It's hand-wavy because of limited knowledge of wind turbulence, but it shows the factors that come into balance.<br /> <br /> <i>"Often, the nocturnal lapse rate is forced closer to the DALR due, I think, to radiative heat exchange. (the radiative equilibrium lapse rate is of course larger than the DALR"</i><br /> Inversion takes you further from the DALR. Radiative heat exchange is less at night, even though the net E/M flux is strongly up. It's not obvious to me that the radiative equilibrium gradient is larger than the DALR. If it were, then there would have to be a very effective counter-pump. <br /> Nick Stokeshttps://www.blogger.com/profile/06377413236983002873noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-47342917916855416992014-11-03T04:52:48.705+11:002014-11-03T04:52:48.705+11:00Living in Finland I can observe the importance of ...Living in Finland I can observe the importance of low altitude inversion in many ways. A strong inversion is common in winter but it's prevalence varies highly from time to time. One consequence of this is that monthly average temperatures vary much more in winter than in summer. The difference between the warmest and coldest January on record is 17.9C, while the difference is about 8C from April to October. Calm clear nights are the major factor in that, but in some cases inversion may persist trough the day. Variations in winter temperature seem to tell much about anything more persistent than variations in summer temperatures.<br /><br />The radiative heat exchange within the atmosphere itself is not the reason for exceeding DALR. The essential reason for that is the heating of the surface by both solar radiation and DWLR. That would result in absence of convection to the high lapse rate. The radiative processes would then be important in heating the lowest troposphere to essentially the temperature of the surface and further to the steep temperature profile through much of the troposphere. When the surface is cold this mechanism does not work and the atmosphere becomes stable against vertical convection.<br />Pekka Pirilähttps://www.blogger.com/profile/04747229036782463233noreply@blogger.comtag:blogger.com,1999:blog-7729093380675162051.post-62624195326235665152014-11-03T04:05:29.043+11:002014-11-03T04:05:29.043+11:00Steve, indeed, the effect of water vapor on radiat...Steve, indeed, the effect of water vapor on radiative heat transfer is what came to my mind when I saw this sentence from Nick:<br /><br /><i> The thing about the moist ALR is that water only has a big effect when it actually changes phase.</i><br /><br /><br />It's worth reiterating that the dry adiabatic lapse rate (DALR) is a condition for stability, it's not actually a predicted lapse rate. It sets an upper limit on the (magnitude) of rate of change of temperature with height, but it isn't really a theory that predicts what environmental lapse rate (ELR) you would actually observe (in general).<br /><br />But, if you look at actual profile data, what you find is you <i>typically do see</i> lapse rates that approach the DALR, but this is the region at the top of the atmospheric boundary layer. Presumably this is because this region is dominated by forced convection, so for this specific case, we expect to find ELRs that approach the DALR limit.<br /><br />It's probably not a surprise that the polytropic approximation works here, because isentropic is one special case of that more generalized relationship.<br /><br />At night time, as is well known, a low-altitude inversion is typically set up by cooling near the surface. Above this in a region called the "residual layer", because the daytime profile that is set up by forced convection is stable, <i>typically</i> what you see is a retention of this daytime lapse rate. This assumes you don't have weather or topography related processes that mix up the layer of course. <br /><br />Often, the nocturnal lapse rate is forced closer to the DALR due, I think, to radiative heat exchange. (the radiative equilibrium lapse rate is of course larger than the DALR, so radiative heat exchange will force the lapse rate to approach that the DALR stability limit.)<br /><br />In the "free layer", you almost never see anything approaching the DALR. Typically, the lapse rate shows curvature with height in this region. I believe that this is due to the increase in horizontal wind speed as you approach the tropopause.<br /><br />If horizontal wind gradients are driving the vertical temperature profile in the free layer, there is no reason to expect any particular relationship between pressure and specific volume, and I'd expect the polytropic approximation to not be valid for that case.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.com