date: Fri, 15 Feb 2008 08:55:32 -0700
from: Aiguo Dai <adai@ucar.edu>
subject: Re: A paper you're doing
to: Phil Jones <p.jones@uea.ac.uk>

   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

