RealClimate: Unforced variations: Sep 2023
3 min read
in Re to
https://www.realclimate.org/index.php/archives/2023/09/unforced-variations-sep-2023/#comment-814260 ,
https://www.realclimate.org/index.php/archives/2023/09/unforced-variations-sep-2023/#comment-814204
and to
Dear zebra, Barton Paul, Piotr,
I am really happy that Barton Paul’s contribution pushed the discussion about the role of water cycle in Earth climate regulation significantly forward.
Before we conclude at least the first part thereof, regarding the role of latent heat flux from the surface, let me add two additional examples that I promised in my reply
https://www.realclimate.org/index.php/archives/2023/09/unforced-variations-sep-2023/#comment-814267
to BPL.
Let us now, instead of BPL’s GEB representing the “preindustrial” Earth, consider another GEB representing the recent “industrial” Earth.
As example can serve the scheme that I used in two examples of my previous post
(all values in W/m^2):
Fabs = 77
Fconv = 105 ( = 85.5 latent heat flux Flh + 18.5 sensible heat flux Fse)
F sol = 163
F = 240
Frad = 399
Fwin = 20
Fatm = 377
Fup = 220
Fgreen = 341
I will desist from assessing whether or not the changes in particular energy fluxes in comparison with the “preindustrial” GEB presented by Barton Paul may or may not be significant. Let us just take as a fact that the ratio x = Fwin/Frad is only 0.0501253133 in this example (compare with 40/776 = 0.106382979 considered by BPL) and k = Fup/Fgreen is now 0.645161290 (compare with 200/323 = 0.619195046 considered by BPL).
Let us now assume a humble change of Fconv, by increasing it to 106 or decreasing it to 104 W/m^2.
First of all, let us look on the most simplified treatment assuming that Earth atmosphere is totally opaque for infrared radiation (Fwin = 0, Fatm = Frad, x = 0). This is the approach I applied till Barton Paul recently encouraged me to consider the “atmospheric window” as well.
In this simplest approach, the change in Fconv is fully compensated by an opposite change in Frad. All other fluxes remain unchanged, and the same is fulfilled for the ratio k = Fup/Fgreen. Please note that in my above cited previous post
I showed that Piotr’s requirement (that the k does apply not only in the final balance but also for the assumed increment delta Fconv) is hardly applicable because it results in an imbalance of energy fluxes in the atmosphere.
Let us now treat the “recent” GEB with Fconv increased to 106 W/m^2 properly, considering the atmospheric window.
Algebraic solution of the equations representing the respective balances provided
Fgreen = (F – (Fsol – Fconv)x)/(k + x) = 341.0720933
Frad = Fsol – Fconv + Fgreen = 398.0720933
Fwin = xFrad = 19.95348828
Fatm = Frad – Fwin = 378.118605
Fup = kFgreen = 220.0465117
I interpret this result the way that in GEBs representing the present Earth with a “five-percent” atmospheric window, the influence of a certain increase in latent heat flux on the surface temperature is slightly attenuated by ca 7 % of this increase returning to Earth surface in form of an increased downwelling infrared radiation from the atmosphere.
In the opposite example with Fconv decreased to 104 W/m^2, the respective results are
Fgreen = (F – (Fsol – Fconv)x)/(k + x) = 340.9279073
Frad = Fsol – Fconv + Fgreen = 399. 9279073
Fwin = xFrad = 20.04651153
Fatm = Frad – Fwin = 379.8813958
Fup = kFgreen = 219.9534885
In case of Barton Paul’s example with a broader “ten-percent” atmospheric window, the decrease in the Frad caused by 11.1 increase in Fconv was 9.47 W/m^2 (ca 85 % of the increase in latent heat flow only).
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My understanding to these results (proposal of an interim conclusion)::
In accordance with climatology textbooks, latent heat flux from Earth surface to the atmosphere is an important factor participating in Earth surface temperature regulation.
The weaker is the atmosphere opacity with respect to longwave infrared radiation (and the higher proportion of the surface radiation is not captured in the atmosphere and escapes directly to the space), the less pronounced is the cooling effect of the non-radiative heat transport. In case of missing or very narrow atmospheric window, latent heat flux cools the Earth surface effectively, like a huge heat pipe.
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Before I move to discussion of parts 4 and 5 of Barton Paul’s analysis that address the relationship between water cycle intensity and water vapour concentration in the atmosphere, I would like to ask if you have any objections against the summary provided above or a different view thereon.
Thank you in advance and greetings
Tomáš
