Friday, May 4, 2012

3837.txt

date: Fri Aug 5 16:12:50 2005
from: Phil Jones <p.jonesatXYZxyz.ac.uk>
subject: Re: DTR trends
to: "Russell Vose" <Russell.VoseatXYZxyza.gov>, Adrian.SimmonsatXYZxyzwf.int

Adrian,
Russ and me have been having some email exchanges about which of your
two datasets we need. We have maps of DTR from Russ (the one he emailed
you an hour or so ago) and from Aiguo Dai and Lisa Alexander.
I've been concentrating on Australia (as we have maps of trends from BoM
for 1950-03 and 1979-03 (attached). Maybe Australia isn't the best place to
look but we're confident BoM is likely to be right.
Of the time series you sent, Australia shows the largest difference between the
0-6h forecast and the 6 hrly analyses, particularly from about 1990. This divergence
since 1990 also occurs in other regions although not over North America nor much
over Europe, which suggests it is something to do with the data. This divergence
isn't an issue in the mean temp from the 2004 paper, so any thoughts.
Russ thinks the 6 hrly analyses look better compared to his plot, but I reckon
that the 0-6hr forecasts are better in some regions.
So, is it possible to send both datasets. Russ can cope with the format.
Cheers
Phil
At 14:31 05/08/2005, Russell Vose wrote:

Adrian:
Many thanks for these figures. At first glance it appears that my analysis for
1979-2004 and yours for 1979-2001 (6-hrly analysis) exhibit some general agreement.
It's not a perfect match, but both suggest that many areas (western U.S., Europe,
western Asia, Australia) experienced an increase in DTR since 1979.
Do you have a global (land surface) trend for 1979-2001 for the 6-hrly analysis?
Adrian Simmons wrote:

Phil
Attached are a set of results based on DTR computed both from the max/min temperatures
in the four daily 0-6h forecasts and from the max/min of the analysed temperatures for
00, 06, 12 and 18UTC. No mask based on CRUTEM2V has been applied, but I've masked out
sea points, based on selecting only 5deg boxes that are more than 50% land.
The first two attachments show maps of the least-square linear trends in DTR computed
for 1958-2001 and 1979-2001. The third attachment shows time series of some area
averages. These are plotted as deviations from the 44-year mean, and smoothed by a
12-month running average. Clearly there are some things here that must be treated with
much suspicion - the drop from the 60s to the mid-70s in the tropics (and southern
hemisphere?) for example is suggestive of a shift in the assimilation associated with
change in data coverage. perhaps, though, there is something useful in the information
for Europe (at least from 1967 onwards after the SYNOP coverage improves) and North
America.
Best regards
Adrian
Phil Jones wrote:

Adrian,
Is it a trivial exercise for you to work a trend from land regions of DTR (annual)
for 1979-2001? I'm just after a number. Does ERA-40 have DTR still going down?
CRU mask not essential. Omit Antarctica.
If it isn't trivial then don't bother.
Cheers
Phil
At 17:04 03/08/2005, Adrian Simmons wrote:

Phil, Russell
As promised earlier, attached is the first of the datasets. It is the set of
monhtly-averages of the daily maximum two-metre temperature, computed from the four 0-6h
forecasts per day carried out from the ERA-40 analyses.
Once you have run gunzip on the dataset, you should be left with a simple character
file, suitable for a formatted read into a FORTRAN program. Looking at the file with any
editor, you should see a sequence comprising a month identifier (format is I4,I2)
showing YYYYMM and then the field itself. Each row (format 72f7.2) contains the
temperature in Kelvin for grid boxes running east from the dateline, ie for longitudes
180W-175W, 175W-170W, 170W-165W,..., 175E-180E, as in the CRUTEM2V dataset downloadable
from the CRU website. There are 36 rows running from north to south, ie for latitudes
90N-85N, 85N-80N,80N-75N,...,85S-90S. The months run from 1958 1 to 200112.
If you can read the data without problem, I'll send the corresponding monthly-average
minimum temperatures computed the same way, and the alternative monthly averages of the
max/min temperatures computed each day from the 00, 06, 12 and 18UTC analyses. I'll send
one field per email to avoid hitting possible mailbox limits.
Best regards
Adrian
--
--------------------------------------------------
Adrian Simmons
Head of Data Division
European Centre for Medium-Range Weather Forecasts
Shinfield Park, Reading, RG2 9AX, UK
Phone: +44 118 949 9700
Fax: +44 118 986 9450
--------------------------------------------------

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.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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--
Russell S. Vose, Chief
Climate Analysis Branch
National Climatic Data Center
151 Patton Avenue
Asheville, North Carolina 28801
Phone: (828) 271-4311
Fax: (828) 271-4328
E-mail: Russell.VoseatXYZxyza.gov

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.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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