From	Peter Thorne	Date	Wed, 02 Jan 2008 10:08:31 +0000
To	Susan Solomon
CC	Tom Wigley, Thomas R Karl, John Lanzante, carl mears, David C. Bader, Dian J. Seidel, francis, Frank Wentz, Karl E.Taylor, Leopold Haimberger, Melissa Free, Mike MacCracken, Phil Jones, Ben Santer, Steven Sherwood, Steve Klein, Tim Osborn, Tom Wigley, Myles Allen, Bill Fulkerson
Subject	Re: Douglass et al. paper
Susan et al., I had also seen the Forster et al paper and was glad to see he had followed up on work and ideas we had discussed some years ago when he was at Reading and from the Exeter workshop. At the time I had done some simple research on whether the stratosphere could affect the tropical troposphere - possibly through convection modification or radiative cooling. I'd done a simple timeseries regression of T2LT=a*Tsurf+b*T4+c and got some regression coefficients out that suggested an influence. Now, this was with old and now discredited data and the Fu et al. technique has since superseded it to some extent (or at least cast considerable doubt upon its efficacy) ... it would certainly be hard to prove in a regression what was cause and effect with such broad weighting functions even using T2LT which still isn't *really* independent from T4. But one thing I did do to try to "prove" the regression result was real is take the composite differences between QBO phases on 45 years of detrended (can't remember exactly how but I think I took differences from decadally filtered data) data from radiosondes (HadAT1 at the time). This showed a really very interesting result and suggested that this communication if it was real went quite far down in to the troposphere and was statistically significant, particularly in those seasons when the ITCZ and QBO were geographically coincident. I attach the slide for interest. I think this is the only scientifically valid part of the analysis that I would stand by today given the rather massive developments since. I doubt that raobs inhomogeneities could explain the plot result as they project much more onto the trend than they would onto this type of analysis. The cooling stratosphere may really have an influence even quite low down if this QBO composite technique is a good analogue for a cooling startosphere's impact, and timeseries regression analysis supports it in some obs (it would be interesting to repeat such an analysis with the newer obs but I don't have time). A counter, however, is that surely the models do radiation so those with ozone loss should do a good job of this effect. This could be checked in Ben's ensemble in a poor man's sense at least because some have ozone depletion and some don't. The only way this could be a real factor not picked by the models, I concluded at the time, is if models are far too keen to trigger convection and that any real-world increased radiative cooling efficiency effect is masked in the models because they convect far too often and regain CAPE closure as a condition. On another matter, we seem to be concentrating entirely on layer-average temperatures. This is fine, but we know from CCSP these show little in the way of differences. The key, and much harder test is to capture the differences in behaviour between layers / levels - the "amplification" behaviour. This was the focus of Santer et al. and I still believe is the key scientific question given that each model realisation is inherently so different but that we believe the physics determining the temperature profile to be the key test that has to be answered. Maybe we need to step back and rephrase the question in terms of the physics rather than aiming solely to rebutt Douglass et al? In this case the key physical questions in my view would be: 1. Why is there such strong evidence from sondes for a minima at c. 500? Is this because it is near the triple point of water in the tropics? Or at the top of the shallow convection? Or simply an artefact? [I don't have any good ideas how we would answer the first two of these questions] 2. Is there really a stratospheric radiative influence? If so, how low does it go? What is the cause? Are the numbers consistent with the underlying governing physics or simply an artefact of residual obs errors? 3. Can any models show trend behaviour that deviates from a SALR on multi-decadal timescales? If so, what is it about the model that causes this effect? Physics? Forcings? Phasing of natural variability? Is it also true on shorter timescales in this model? It seems to me that trying to do an analysis based upon such physical understanding / questions will clarify things far better than simply doing another set of statistical analysis. I'm still particularly interested if #2 is really true in the raobs (its not possible to do with satellites I suspect, but if it is true it means we need to massively rethink Fu et al. type analysis at least in the tropics) and would be interested in helping someone follow up on that ... I think in the future the Forster et al paper may be seen as the more scientifically significant result when Douglass et al is no longer cared about ... Happy new year to you all. Peter -- Peter Thorne Climate Research Scientist Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB tel. +44 1392 886552 fax +44 1392 885681 www.metoffice.gov.uk/hadobs Attachment Converted: "c:\eudora\attach\qbo_slide.ppt"