tag:blogger.com,1999:blog-2219566526148503794.post8733253927147495347..comments2023-06-09T05:51:20.174-07:00Comments on Climate Consensarian: Lapse Rate on Venus, Part 2Brandon R. Gateshttp://www.blogger.com/profile/17031044715994785956noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-2219566526148503794.post-4275302590106938722019-11-09T03:57:11.142-08:002019-11-09T03:57:11.142-08:00A very nice observation, Lisa.A very nice observation, Lisa.Rod Martin, Jr.https://www.blogger.com/profile/18338151864062902878noreply@blogger.comtag:blogger.com,1999:blog-2219566526148503794.post-40597307768952150872018-10-01T12:39:58.413-07:002018-10-01T12:39:58.413-07:00Hey, just a comment. The haze layer starts around ...Hey, just a comment. The haze layer starts around 40 km. From 0-40km has very little convection and very little temp differences and is clear even though the day night cycle is ridiculously long. This indicates that the surface layer 0-40km is extremely stable. All the Earthlike convection starts above the 40km where your observed lapse rate deviates from the predicted. The falling sulfuric acid has evaporated below 40km so the entire acid "rain" cycle occurs between 40km and the cloud tops. Don't know if that matters to your analysis but 0-40km is not a typical earthlike troposphere. Lisa K.https://www.blogger.com/profile/14704389440608624989noreply@blogger.comtag:blogger.com,1999:blog-2219566526148503794.post-6139262549526135932016-03-08T13:35:11.674-08:002016-03-08T13:35:11.674-08:00I'm guessing a close comparison because there ...I'm guessing a close comparison because there isn't much if any heating of the surface from the sun. Convection is slow based on the two-month long days and apparently doesn't take much to keep such a stable atmosphere, from what I read.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2219566526148503794.post-50191534554884417912016-03-08T13:34:23.869-08:002016-03-08T13:34:23.869-08:00I'm guessing a close comparison because there ...I'm guessing a close comparison because there isn't much if any heating of the surface from the sun. Convection is slow based on the two-month long days and apparently doesn't take much to keep such a stable atmosphere, from what I read.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2219566526148503794.post-30631598782489959812016-03-08T12:54:27.990-08:002016-03-08T12:54:27.990-08:00Chic, Part 2:
Finally and MOST IMPORTANT. The val...Chic, Part 2:<br /><br /><i>Finally and MOST IMPORTANT. The value for Cp of Venus (mostly CO2) that you used in Figures 1, 2, and 4 is 850 m2/s2K.</i><br /><br />Justified by one seemingly credible reference. I'm not going to say that it's unimpeachable. I used it because it made more sense to me at the time.<br /><br /><i>The commonly used unit for Cp is J/g-K. The specific heat capacity refers to the change from molar heat capacity where the units are J/mol-K. Dividing by the molecular weight gives you the specific heat capacity in J/g-K. One J is one kg-m2/s2.</i><br /><br />Ah. Curses, you're right. I will eat my crow and amend the head post accordingly, thank you.<br /><br /><i>So if you multiply 850 m2/s2K by 1kg/1000g you get 0.85 Kg-m2/s2/g-K or J/g-K. So don't throw away that Figure 6 that you think is just a coincidence.</i><br /><br />I won't, but I'm still skeptical, nay dubious, of the result because it's my understanding that convection doesn't happen unless (absolute) temperature is greater than the (absolute) temperature "predicted" by the adiabat.Brandon R. Gateshttps://www.blogger.com/profile/17031044715994785956noreply@blogger.comtag:blogger.com,1999:blog-2219566526148503794.post-63014662081870725452016-03-08T12:53:40.711-08:002016-03-08T12:53:40.711-08:00Chic,
The lapse rate can't predict absolute t...Chic,<br /><br /><i>The lapse rate can't predict absolute temperatures for the reasons we agreed on in the competing mechanisms thread.</i><br /><br />Indeed. I should not continue harping on it as if you and I haven't reached that agreement. I'm still emphasizing it because some of the references you provided on the competing mechanisms thread -- to my eyes -- imply that it does.<br /><br /><i>Therefore Cp can and does vary with pressure.</i><br /><br />No dispute. Today is the day I write Part 3, and I will deep-dive into Cp.<br /><br /><i>For that reason, I don't consider your adjusting the lapse rate "under" rather than "over" the observed lapse rate a goof. It very nicely illustrates the value and the limitations of comparing a calculated with an observed value.</i><br /><br />Agree with the latter sentence. I've been proceeding from the assumption that lapse rate calculations are "cleaner" on Venus because it's a (mostly) dry atmosphere, and so dense that theory should track to (estimated) reality rather better than on Earth. An outstanding question is the uncertainty in the observations.<br /><br />I should clarify what I meant by the goof, which was assuming that the tropopause was 30 km instead of 60 km, and forcing the lapse rate curve to intercept observation at 60 km. Convention apparently works from the bottom up, and thus forces an x-axis intercept at the surface temperature.<br /><br />In short, whatever I choose for Cp for whatever reason, the diagram makes more sense "pegging" the absolute temperature of the lapse rate curve to the surface temp.<br /><br /><i>I think the incorrect Cp value used to calculate a lapse rate is what made your prediction dead wrong. But choosing the known value of the surface temperature as an intercept, what is your interpretation for the point at 30 km?</i><br /><br />I'm not sure yet. From the shape of the actual temperature profile, 30 km does not look like the tropopause to me, 60 km does. I see from your comments below that we have similar thinking.<br /><br /><i>Isn't tropopause where the lapse rate no longer applies?</i><br /><br />Yes, exactly. When convection stops, so does lapse rate because there's little to no overturning to cause change in pressure, so no more adiabatic compression/expansion driving temperature change.<br /><br /><i>The usual explanation is the air above is heated by SW and that kills any further convection from the tropopause.</i><br /><br />I hadn't seen it described that way, and it's not how I think about it -- which is that cooling is what kills tropospheric deep convection. That the stratosphere is heated from the top down is what keeps it stable, and thus it has a positive lapse rate attributable to radiative heating by downwelling SW, primarily UV.<br /><br /><i>I would say Venus' tropopause is around 80 km, not 30 km.</i><br /><br />Yes, somewhere between 60-80 km makes more theoretical sense to me just from looking at the actual temperature profile. As I allude above, finding that one source puts Venus' tropopause at 30 km threw me for a loop. It doesn't make sense to me.Brandon R. Gateshttps://www.blogger.com/profile/17031044715994785956noreply@blogger.comtag:blogger.com,1999:blog-2219566526148503794.post-9842732096852828012016-03-08T10:16:32.042-08:002016-03-08T10:16:32.042-08:00"...a lapse rate that predicts a higher absol..."...a lapse rate that predicts a higher absolute temperature throughout a known convective atmospheric regime is also nonsense."<br /><br />The lapse rate can't predict absolute temperatures for the reasons we agreed on in the competing mechanisms thread. Also, I see we have a disagreement over the units (see my last paragraph). The lapse rate for Venus should vary between 7.4 and 10 K/km reflecting the change in Cp due to pressure. IOW Cp is the change in energy with respect to temperature when pressure is held constant. Therefore Cp can and does vary with pressure.<br /><br />For that reason, I don't consider your adjusting the lapse rate "under" rather than "over" the observed lapse rate a goof. It very nicely illustrates the value and the limitations of comparing a calculated with an observed value.<br /><br />"Unfortunately, my visual convenience lead to making physically untenable (i.e. dead wrong) predictions about what absolute surface temperature 'should be' at the surface were it not for convection."<br /><br />I think the incorrect Cp value used to calculate a lapse rate is what made your prediction dead wrong. But choosing the known value of the surface temperature as an intercept, what is your interpretation for the point at 30 km? <br /><br />"In the atmosphere, IR light can be absorbed and re-emitted multiple times before its energy reaches the emission level where it is free to escape to space (Pierrehumbert 2011)."<br /><br />I don't know why you think you have to repeat this to me. What I have to keep repeating to you is the emission level part. Near the surface these absorptions and emissions cancel out. Only when the density of the atmosphere thins, does the net LW radiation go to space. There should be no disagreement on that or you are disagreeing with Peirrehumbert himself.<br /><br />Benestad's "emission temperature of 254K at around 6.5 km above the ground" translates to 5.2 K/km lapse rate. But he doesn't call it that. Instead it is a "radiative heating profile" due to convective adjustment. The standard atmosphere vertical temperature profile is 6.5 K/km not 5.2 K/km.<br /><br />Isn't tropopause where the lapse rate no longer applies? The usual explanation is the air above is heated by SW and that kills any further convection from the tropopause. I would say Venus' tropopause is around 80 km, not 30 km.<br /><br />Finally and MOST IMPORTANT. The value for Cp of Venus (mostly CO2) that you used in Figures 1, 2, and 4 is 850 m2/s2K. The commonly used unit for Cp is J/g-K. The specific heat capacity refers to the change from molar heat capacity where the units are J/mol-K. Dividing by the molecular weight gives you the specific heat capacity in J/g-K. One J is one kg-m2/s2. So if you multiply 850 m2/s2K by 1kg/1000g you get 0.85 Kg-m2/s2/g-K or J/g-K. So don't throw away that Figure 6 that you think is just a coincidence.Anonymousnoreply@blogger.com