cc: <trenbert@ucar.edu>, <Albert.Klein.Tank@knmi.nl>, Jay Lawrimore <Jay.Lawrimore@noaa.gov>, Byron Gleason <Byron.Gleason@noaa.gov>, david.easterling@noaa.gov 
date: Fri Jul 15 11:40:55 2005
from: Phil Jones <p.jones@uea.ac.uk>
subject: Fwd: RE: [Fwd: Re: [Fwd: Re: Some more thoughts on DTR map for
to: <l.alexander@bom.gov.au>

    Lisa et al,
       Thanks. Forwarding to the others at NCDC involved in all the discussions.
    I think the main conclusion to draw from all this is that 1979-2004 is too short
    a period.
        If Russ produces a map for 1951-2004 then hopefully they will all look much
    more similar. We should likely go with one of these plots. We probably need
    to consider if we want a trend map. I would say yes, as if we get the right one, it
    will show that DTR is decreasing as an average, but definitely not in many locations.
        There are certainly lots of potential problem areas as Lisa alludes to, as does
    the detail from Aiguo.
    Cheers
    Phil

     Reply-To: <l.alexander@bom.gov.au>
     From: "Lisa Alexander" <l.alexander@bom.gov.au>
     To: "'Kevin Trenberth'" <trenbert@ucar.edu>,
             "'Phil Jones'" <p.jones@uea.ac.uk>,
             "'Klein Tank, Albert'" <Albert.Klein.Tank@knmi.nl>
     Subject: RE: [Fwd: Re: [Fwd: Re: Some more thoughts on DTR map for 1979-2004]]
     Date: Fri, 15 Jul 2005 20:07:11 +1000
     Organization: BMRC, Bureau of Meteorology - Australia
     X-Mailer: Microsoft Outlook, Build 10.0.2627
     Hi all,

     I have plotted up the 1979-2003 DTR trends using the global extremes data.  Ive tried to
     use a similar colour scheme and range to Aiguo since he also has trends for the longer
     period.  Things to note:-

     1.  I have only used quality controlled stations which have at least 40 years of data
     between 1951-2003.  This is because otherwise I would have had to regrid all of the data
     which would take some more time to complete.  The spatial coverage would be better if I
     say regridded using stations that had at least 20 years of data between 1979 and 2003
     and this might be something worth considering.

     2.  Figure caption:-  Observed trends per decade for 1979-2003 for the diurnal
     temperature range index.  Trends were calculated for grid boxes which had at least 20
     years of data during this period and ended no later than 1999.  Black lines enclose
     regions where trends are significant at the 5% level using the method of Wang and Swail,
     [2001].

     3. I have used the HadCM3 grid size (2.5 x 3.75).

     4. There are very few areas showing significant change.

     We can safely say that there is not general agreement between the 3 results!  I agree
     well with Aiguo in some regions and with Russ in others.  For comparison I asked Dean
     Collins to plot DTR trends for Australia for the two periods (attached).  I would say
     that Russ and I agree better over Australia than Aiguo.  Since Dean and I source the
     same daily data our results should be similar but there are some differences in detail
     which would need to be checked out.  Aiguo and I agree better in terms of the sign of
     the trend over South America but not in magnitude.

     I have not read Russs or Aiguos papers so I cant comment on their methods.  Potential
     areas of discrepancy are:

    1. Are we all using exactly the same definition of DTR?
    2. Data sources.
    3. Different gridding methodologies.
    4. Different trend calculation methodologies and missing data tolerance.


     One might suggest that the sample size is too small to accurately calculate trends over
     25 years.  However it is quite worrying that the sign of the trend can be so different
     between the methods.  When I calculated the correlation decay distances for the paper,
     DTR was one of the less coherent indices which may be a factor.

     For some reason Im having trouble getting the percentile maps and timeseries diagram
     exactly how you want them.  Perhaps its because its Friday.  Im attaching what I have so
     far.  Y-axis now represents the anomalies in days.  Perhaps Ill have better luck on
     Monday.

     Regards.

     Lisa.

     -

   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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