Friday, May 4, 2012

3844.txt

cc: David Easterling <David.EasterlingatXYZxyza.gov>, trenbert@ucar.edu, Aiguo Dai <adaiatXYZxyz.ucar.edu>, l.alexander@bom.gov.au, Byron Gleason <Byron.GleasonatXYZxyza.gov>
date: Tue Jul 26 16:55:44 2005
from: Phil Jones <p.jonesatXYZxyz.ac.uk>
subject: Re: DTR follow-up
to: "Russell Vose" <Russell.VoseatXYZxyza.gov>

Russ,
The work with Adrian will help in the long-term, but not in the short term here (i.e.
Aug 12). Let's discuss that possibility later.
Also can you arrange for WWR91-00 to get sent at some time. Is it all on a
CD, for example. That would be fine. If books have been produced, they are always
useful - and do get used in our library. We would like them, not asap, so if books
are available, they can come on a slow boat.
The HC said they had found some errors with station level and SLP. It was
Rob Allan, so only looking at pressure.
As for the matter in hand. Can you send this group, time series plots for
1950-2004 for annual max/min/dtr, so we can compare with the figure we
currently have in the draft ? Dave a copy of this. Maybe plot with/without the
suspect Argentinian stations.
An issue with these plots might be the last 2-3 years. Do they significantly
impact the trends, for example? Aiguo's data must use synops for 2001-4. You
note problems using this source via your pt 7 earlier.
We do need resolution, but I'm not sure we will get it.
Cheers
Phil
At 15:26 26/07/2005, Russell Vose wrote:

Phil:
Thanks for the feedback.
How much longer would you recommend I continue to look at regional-scale discrepancies?
I'm wondering because my data "sensitivity" tests aren't having a huge impact. For
instance, I removed all Argentinian stations derived from GHCN-Daily (i.e., the those
with data disagreements with other sources from 1984-87). The DTR trends dropped as a
result, which was expected, but most trends are still slightly positive in that area.
As far as the work with Adrian Simmons goes -- might be a really useful Q/A tool. We
should discuss further because it could impact how I merge stations in the future.
The global/annual DTR trend from 1979-2004 is 0.0036 C/dec if you include the suspect
Argentinian stations and -0.0033 C/dec if you exclude them. Neither is anywhere close
to statistically significant.
Both are based on a 1979-2004 base period, 21 years of data, etc.
We might have sent the WWR 1991-2000 data to the HC. Hope they got the clean data!
Just let me know when you want it.
Regarding the impending deadline -- I'm on it, or it's on me!
Phil Jones wrote:

Russ,
Thanks for the summary. The results you're getting in 4) and 5) seem to confirm
that you've got the overall numbers right, but the detail for South America and
other regions will be where the goodness of the results stands or falls. So,
continue the work on sorting this out.
The work we planned with Adrian Simmons with the ERA-40 data would
seem more important. This highlighted a few problems with the CRU data for
mean temperature. My guess is that a similar comparison might highlight
many more problems, most of which would likely be resolved through looking
at the issues of dataset construction that rest of the decisions you allude to
in 7).
The points you make in 7) just highlight how difficult it is to put together
datasets of this kind, particularly when trying to use daily and hourly data.
We are working to a tight deadline, as you know. What is the DTR trend
over all for 1979-2004?
In the longer term I'd like to get a copy of the WWR dataset for the 1990s.
The HC seem to have a copy of this by the way ! No rush, as I've far too
much on at the moment.
Cheers
Phil
At 22:37 25/07/2005, Russell Vose wrote:

Hi guys...
About two weeks ago I received several e-mails expressing surprise (and concern) over
Fig. 3.2.11, the global map of gridded DTR trends for 1979-2004. Over the past few days
I've conducted several sanity checks to address these concerns. In general, these
checks indicate that the analysis is accurate over large spatial scales, although some
areas may be suspect due to limitations in the underlying station network. In the
following I discuss the various checks performed as well as the results obtained
therein.
1. As a first step I double-checked the calculations by hand and didn't catch any
problems.
2. I computed trends for 1950-93, the Easterling et al. analysis period, using exactly
the same base period as in the Science paper.
As global/annual trends derived from the "NCDC" dataset were within 0.02 C/dec of Dave's
results (slight differences are to be expected given differences in spatial coverage).
Furthermore, trend maps prepared from the NCDC dataset are VERY similar to Easterling et
al.
3. I evaluated trends for 1979-2004 using two record length thresholds: 18 years (67%)
and 21 years (80%). Note that the former was used in the map you received a couple of
weeks ago. The latter contains slightly less noise, but the patterns are essentially
the same. Specifically, both maximum and minimum temperature increased over virtually
all areas except northwestern Australia and parts of southern South America. As already
discussed in various e-mails, the DTR pattern was much more variable, with somewhat
surprising increases in the same areas (as well as the United States and Europe).
4. I took Phil's suggestion and compared the max/min trends in the NCDC dataset to the
mean temperature trend in GHCN version 2.0, which is used here operationally. For
1979-2004, the maximum temperature trend is 0.284 C/dec, the minimum temperature trend
is 0.280 C/dec, and the mean temperature trend is 0.269 C/dec (again, slight difference
likely results from differences in spatial coverage). Few areas have had decreasing
mean temperature trends during that period, but those that did almost always had a
decrease in the maximum and/or minimum (e.g., southern South America, northwestern
Australia).
5. I followed up on another of Phil's suggestions and evaluated trends from 1950-2004
(using a base period of 1979-2004, requiring 18 years of data during the base period and
36 during the trend period -- not that the results are very sensitive to these
thresholds). As expected, the DTR map is much smoother than for 1979-2004. On the
global scale, the maximum temperature trend was 0.144 C/dec, the minimum was 0.204
C/dec, and the DTR was -0.058 C/dec. The maximum and minimum trends are considerably
larger than Easterling et al. (1997) whereas the DTR is smaller.
6. I have made numerous time series plots for southern South America in an effort to
explain the somewhat surprising trends there. At first I was highly confident in my
data for that area because it is a compendium of records from the Easterling et al.
(1997) paper, the new addition of World Weather Record (which no one has yet), CLIMAT
reports, and GHCN-Daily. In many cases I have data for the same station from more than
one source, and the time series plots suggest that the data during the overlap periods
are very similar. However, by the end of today I had identified 13 stations that may
have suspect data from 1984-87.
Specifically, the GHCN-Daily data for this period disagrees with the other sources in a
manner which may result in an increasing DTR trend.
Unfortunately, I have no way of knowing which source is correct (majority doesn't rule
in this business). I'll try to sort that out in the next day or so.
7. For the record, we actually computed monthly mean maximum and minimum temperature for
all stations in the Integrated Surface Hourly (i.e., synoptic) database for the entire
period of record. There are many decisions one must make along the way (e.g., what
observation time should one use, should one make assumptions about missing "period
quantities", how many days must have data when computing a monthly mean). We basically
found those decisions had a huge impact on the results. Consequently, I made only very
limited use of these data in the analysis -- basically applied them to fill a few holes
or extend the record when the agreement seemed reasonable for certain quantitative
checks and on time series plots.
--
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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--
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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