From: Phil Jones <p.jones@uea.ac.uk>
To: Aiguo Dai <adai@cgd.ucar.edu>, Kevin Trenberth <trenbert@ucar.edu>
Subject: Re: more on section 3.7 and Marengo
Date: Thu May  5 08:45:53 2005
Cc: Jim Renwick <j.renwick@niwa.co.nz>, Panmao Zhai <pmzhai@cma.gov.cn>, Matilde Rusticucci <mati@at.fcen.uba.ar>, "'David R. Easterling'" <david.easterling@noaa.gov>

    Kevin et al,
         The diagram looks too good to me. CRU's data are reasonable over Brazil for
    some of the period, but poor in others, particularly recently. So we would have
    difficulty in updating this because of station numbers and quality. We could try
    using the GPCC dataset. They have huge numbers of stations for Brazil, but only
    for specific regions and periods, so likely problems there also.
         We have a couple of papers in submission to J. Hydrology on flows in the
    subcatchments of the Parana river, which are well reproduced by rainfall,
    evaporation and a catchment model. Agree with your concerns about the Amazon
    flows not agreeing with the rainfall. Do the NAR and SAR regions fully encompass
    the enormous catchment though.
    Cheers
    Phil

   At 17:36 03/05/2005, Aiguo Dai wrote:

     One can use the Chen et al. and CRU to produce similar type of  plots to validate
     Marengo's  result.
     He did use the CRU rainfall data set, but not for this particular plot.
     Aiguo
     Kevin Trenberth wrote:

     Hi all
     As you know we got some manuscripts from Jose Marengo to be considered in our chapter,
     and he is a LA on another chapter and will be in Beijing.  He has offerred to be  CA.
     My question concerns how good his data are?  I asked Aiguo Dai to comment:
     ====
     One of the interesting results from Marengo's work is that he found the Northern and
     Southern Amazonia have opposite phase of decadal rainfall variations (see attached Fig.
     from Marengo 2004, Ther. Appl. Climatol.): In the northern Amazonia,  rainfall is above
     normal during ~1945-1975 and below normal during ~1976-1998; and it is opposite in the
     southern Amazonia. He suggested warmer SST in central and eastern Pacific contributed to
     the dry conditions in the northern Amazonia during 1976-1998.
     As noted in Betts et al. (2005, JHM, in press), Marengo's basin integrated rainfall
     index does not correlate well with Amazon river flow during the recent decades (worse
     than Chen et al.). This large multidecadal signal seems, however, robust.
     =====
     Certainly the attached figure is striking.  Are we sure it is not due to changes in the
     way observations are made? Do other datasets replicate this? The lack of relation with
     river flow is a substantial concern.   Matilde, can you provide informed commentary?  If
     the figure is good then maybe we should include it?
     Kevin

     --
     Aiguo Dai, Scientist                        Email: 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      [1]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    p.jones@uea.ac.uk
   NR4 7TJ
   UK
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References

   1. http://www.cgd.ucar.edu/cas/adai/

