Saturday, August 22, 2009

PM05 resolved?

OK, a little extra thought about this early on a Sunday morning may have identified the source of all the troubles. This post may make more sense if you've already read not only that above linked post, but also this post and this one by Roger Pielke Sr.

The issue seems to be in what this 1Wm-2 forcing "at the surface" actually means. Roger is sucking this out of the bottom of his atmosphere, which results in a huge localised cooling (due to low heat capacity and limited mixing).

Actually, this value appears to represent the radiative forcing of the land surface, not the atmospheric (lower) surface. Note that the land radiates differently from the atmosphere, and some of this radiation does indeed pass directly into space.

Temperature inversions (such as those underlying the PM05 paper, see their Figure 1) arise not by the bottom layer of molecules of the atmosphere pumping out extra heat directly out to space - there is no way for this to happen, the atmosphere is basically just as opaque (or not) at the 10m level as it is at 0m. Temperature inversions arise though the land cooling to space (it can do this, it radiates differently) and only then cooling the lower boundary of the atmosphere.

So if the surface (land) forcing changes by 1Wm-2, this does not directly suck this amount of heat out of the lower atmosphere, and instead only affects the atmosphere in a second-order manner depending on how much less land cooling this results in. (Given that the land sees a typical diurnal range of ~250Wm-2, the answer is going to be "not a lot".) I think it would be a straightforward process to add a simple land surface to the model Roger used (making some assumptions about typical land type), and check the results of 1Wm-2 of surface forcing. I predict the implications for inversion strengths would be completely negligible.

The direct radiative forcing of the atmosphere itself is, as confirmed directly by the pictures Roger helpfully provided, very small indeed near the surface and if anything increasing with height (this depends on the details of atmospheric profile).

8 comments:

Dirk said...

James:

This para:

Temperature inversions...arise not by the bottom layer of molecules of the atmosphere pumping out extra heat directly out to space...(but) arise though the land cooling to space...and only then cooling the lower boundary of the atmosphere.

is spot on and is the reason why RPSr.'s idea of BL forcing TO the surface is so flawed. As I said, it shows stunning ignorance that RPSr has not acknowledged this. Seriously - 1Wm-2 causing a 3K change?

If he had asked any micro-meteorologist - or read the relevant urban climate literature about this - before writing PM05, he would have realized this error.

I think it would be a straightforward process to add a simple land surface to the model Roger used (making some assumptions about typical land type)

Bet you 500 Yen that he won't.

Why? Because doing so (assuming he has realistic assumptions of the surface properties of a typical urban surface) will negate the results of Lin, Pielke et al (2007) - the other paper that he loves to hype up as being the key to his "urban" warming hypothesis.

I predict the implications for inversion strengths would be completely negligible.

There are numerical micro-met climate models out there that have demonstrated just that (hint: google "ENVI-Met" by Michael Bruse).

Dirk said...

Also, I find RPSr's victim bully approach
very grating, immature and unbecoming of someone of his stature. It may play well to the uninformed at WattsUp, but he really should know better if he wants to be taken seriously again by the people who matter.

Roger - if you are reading this - James pointed out to your son that communicating badly and acting smug when you are misunderstood is not cleverness. Sad to see it happen to the father as well.

Steve Bloom said...

Dirk, RP Sr. tipped into this sort of behavior years ago (around the time he retired), although he keeps finding news ways to embellish it (as with his recent declaration that Watts is now part of the "Pielke Research Group"). I'm guessing that the proximate cause was a loss of his major funding (from the NSF for his mesoscale model?).

I was going to suggest reading through his early blog posts to see some of the interesting history, but the most illuminating material is in the comments and these have now been expunged (in a upgrade handled by Watts, who I think has better political judgement than RP Sr.). (James especially will be disappointed that much of his purple prose attempting to set RP Sr, straight on the "butterfly effect" now sleeps with the fishes.)

There's still this post, though, in which RP Sr. cleverly accuses Ralph Cicerone of lying to Congress. Some evidence also remains of his contemporaneous forced resignation as lead author of a CCSP committee dealing with (surprise!) the very same issue we're discussing here today.

The most telling part of the latter post is RP Sr.'s assertion that all of the committee members were just about in agreement with his draft when all of a sudden they changed their minds and signed onto a different one. That sort of persistent cluelessness is something to behold.

EliRabett said...

Tony Watts was ALWAYS a member of the Pielke Research Group. You only had to look at how and where the photo project came from. Now Eli is not saying this was a good thing, nor a bad thing, only that it was always crystal clear for anyone who thought about it

Steve Bloom said...

That's right, Eli, but my point was just that the formalization of the status (which I'm pretty sure is recent) is another brick in the wall RP Sr. is building between himself and scientific credibility.

Martin said...

Note that the land radiates differently from the atmosphere, and some of this radiation does indeed pass directly into space.

James, do I understand correctly that the explanation is the following:

* The ground is a black (well, grey-ish) body that radiates all over the spectrum. For part of this spectrum, the atmosphere is transparent, and there, the ground radiates directly to space.

* Air is a gas. In parts of the spectrum, it is opaque and cannot radiate directly to space. In other parts, it is transparent, and because of Kirchhoff-Bunsen, it also doesn't manage to radiate (although if it could, this radiation would go straight off into space). The only parts of the spectrum where air can directly radiate to space, are where it is "semi-transparent", like the slopes of absorption bands; only a small part of the total spectrum.

Right?

James Annan said...

Martin,

Yes, that's what I understand to be the case (though I'm not an expert on this). The radiating properties of the air change a bit with altitude too.

Martin said...

Thanks James!