date: Fri, 15 Feb 2008 08:55:32 -0700 from: Aiguo Dai subject: Re: A paper you're doing to: Phil Jones Phil, In Dai (2006, J. Clim), I specifically examined the changes in global (both ocean and land) surface q and RH from 1975-2005 and found that sfc q increases with air temperature while RH remains fairly constand (except a few regions in India and the central US where RH increased). Since surface water/latent heat flux is affected, in part, only by RH, not q itself, the changes in surface humidity should not be a major contributor to changes in evaporation. At the last Fall AGU meeting, I showed some prelimiary results on trends in surface wind speed over the globe during the last 30 yrs or so. The sfc obs. show an apparent decreasing trend in surface wind speed over most of the Eurasia, N.A. and other land areas. Although this is consistent with decreasing pan evaporation, I am still trying to make sure the wind data are not showing nonclimatic changes. Aiguo Phil Jones wrote: Aiguo, Thanks. It wasn't me slowing the ms down! Another factor in addition to wind and radiation is vapour pressure. In case you've not seen the attached here it is. Vapour Pressue and q are going up as T goes up. RH stays much the same. We've submitted a longer paper on this dataset. It is rather short though - only going back to 1973. Cheers Phil At 16:49 14/02/2008, you wrote: Hi Phil, The manuscript is attached, which took a while to get through the review process, but look like it will be accepted after some revision. The main conclusion is that changes in wind speed and sfc radiation may be important in water balance calculation for wet regions. Because the PDSI model considers only T and P changes, its application over wet, energy-limited regions may be questionable. We still need to work out this on a global basis. On the other hand, the PDSI results from Dai et al. (2004) illustrate the potential drying from surface warming and precip changes alone, and this drying appears to have happened over many regions (e.g., most Africa, etc.). Aiguo Phil Jones wrote: Aiguo, I hear you're doing a paper with Hobbins, Roderick and Farquhar. Is it possible to send me a copy of this? Cheers Phil Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email [1]p.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- -- Aiguo Dai, Scientist Email: [2]adai@ucar.edu Climate & Global Dynamics Division Phone: 303-497-1357 National Center for Atmospheric Research Fax : 303-497-1333 P.O. Box 3000, Boulder, CO 80307, USA [3]www.cgd.ucar.edu/cas/adai/ Street Address: 1850 Table Mesa Drive, Boulder, CO 80305, USA Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email [4]p.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- -- Aiguo Dai, Scientist Email: [5]adai@ucar.edu Climate & Global Dynamics Division Phone: 303-497-1357 National Center for Atmospheric Research Fax : 303-497-1333 P.O. Box 3000, Boulder, CO 80307, USA [6]www.cgd.ucar.edu/cas/adai/ Street Address: 1850 Table Mesa Drive, Boulder, CO 80305, USA