Thursday, May 3, 2012

3748.txt

cc: Beck Christoph <christoph.beckatXYZxyz.de>, Rudolf Bruno <Bruno.RudolfatXYZxyz.de>
date: Tue May 3 08:25:41 2005
from: Phil Jones <p.jonesatXYZxyz.ac.uk>
subject: Re: AW: Your views appreciated
to: Grieser J�rgen <juergen.grieseratXYZxyz.de>

Jurgen, Bruno and Christoph,
Thanks for the comments. The'll be discussed at the WGI IPCC meeting next week
(May 10-12).
Cheers
Phil
At 16:42 29/04/2005, Grieser J�rgen wrote:

Dear Phil,
Bruno forwarded your todays email to me and I am very glad to be asked to
reply.
Pls find my comments in the attached word document.
In case of further questions, comments, etc. pls don't hesitat to contact me
again.
Best regards from Christoph Beck, Bruno Rudolf and myself,
J�rgen.

********************************************
Dr. Juergen Grieser
Global Precipitation Climatology Centre GPCC
Deutscher Wetterdienst
P.O.Box 10 04 65
63004 Offenbach
Germany
Tel.: +49 -69 8062 2873
Fax: +49 -69 8062 3759
Web: [1]http://gpcc.dwd.de <[2]http://gpcc.dwd.de/>
********************************************


-----Urspr�ngliche Nachricht-----
Von: Rudolf Bruno
Gesendet am: Freitag, 29. April 2005 13:39
An: 'Phil Jones'
Cc: Grieser J�rgen
Betreff: AW: Your views appreciated
Hi Phil,

thank you for contacting us. A very first quick reply:
Yes, what you called the fixed stations versions should be used for the
purpose discussed.
We call it 50 year climatology, because it is optimized for homogeneity, and
it is THE only of our products recommended to use it for climate variability
(trend) studies. And relative anomaly is used for interpolation for this
product.

Juergen Grieser will send a more complete reply on the 50 year climatology.

The Monitoring Product and Full Data Product are based on interpolation of
precipitation totals because we had no normals for many of the stations with
data for the recent years. For the recent years, most data are only
available from SYNOP, and the accuracy of those is very low. Compared to
normals, we partly obtain unrealistic anomalies, which are spatially
exported by gridding. Maps resulting from the anomaly maps combined with
normal maps showed some curious structures, whil the results from direct
interpolation was still plausible. This assessment is based on earlier
studies. We will do the methods comparison again for the currebt version of
the full data basis.

But whatever one does in analysis: if the gauge data base (number of
stations) is very different in time, one will not get a homogeneous product
(my opinion).

Cheers,
Bruno


-----Urspr�ngliche Nachricht-----
Von: Phil Jones [[3]mailto:p.jones@uea.ac.uk]
Gesendet am: Freitag, 29. April 2005 11:16
An: Rudolf Bruno
Betreff: Your views appreciated
Bruno,
Shortly after AOPC, I was back with my IPCC hat on modifying text based
on
reviews of our first zero-order draft. I go to Beijing the week after next
for the next
Lead Author's meeting. By mid-August, we will have a new draft (the
first-order one)
which can be downloaded by anyone over an 8-week period then. I expect many
hundreds will and there will be thousands of comments. That was some
background !
I sent your email about VasClimO to some of the people we've involved
as contributing
authors (CAs) and also to our Lead Author for our precipitation section.
Our LA for this is
Dave Easterling. The details also went to Aiguo Dai (who is with Kevin
Trenberth at NCAR).
My intention was to alert this group to your latest work at GPCC. I said
that your dataset
from 1951 was likely the best available. Our chapter currently has trend
maps for
1901-2004 and 1979-2004 from GHCN gridded fields (Dave Easterling produced
these).
Dave hasn't responded on this yet.
The point of this email is to get your views on the email below from
Aiguo Dai.
We will almost certainly have some time series plots from different data
sources
including GPCC, GHCN, maybe CRU and Chen et al.. What I would like before I
leave for China on May 7 (so by middle of next week) are your brief views
on some
of these other products (e.g. Chen et al. 2002, GPCPv2 from Adler et al.,
2003)?
Would you recommend using your fixed station version?
I am very sympathetic to the view that you should grid using anomalies.
Can you briefly
say why you didn't? If the answers to all these questions are in the
report, tell me
and I'll read it. I've not had time to yet.
I am just trying to get all the views together for the Beijing meeting.
I expect Kevin
Trenberth will want to accept what Aiguo says. For the moment, just reply
to me.
Cheers
Phil
Date: Thu, 28 Apr 2005 16:17:07 -0600
From: Aiguo Dai <adaiatXYZxyz.ucar.edu>
Organization: NCAR, Boulder, CO
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To: Phil Jones <p.jonesatXYZxyz.ac.uk>
CC: trenberth@ucar.edu, Peter Ambenje <omash01atXYZxyzoo.com>,
Roxana Bojariu <bojariuatXYZxyzstral.ro>,
David Easterling <david.EasterlingatXYZxyza.gov>,
David Parker <david.parkeratXYZxyzoffice.gov.uk>,
Fatemeh Rahimzadeh <rahim_fatXYZxyzmet.net>, Jim Renwick
<j.renwickatXYZxyza.co.nz>,
Matilde Rusticucci <matiatXYZxyzfcen.uba.ar>,
Brian Soden <bsodenatXYZxyzas.miami.edu>, Panmao Zhai <pmzhai@cma.gov.cn>,
Albert Klein Tank <Albert.Klein.TankatXYZxyzi.nl>,
Aiguo Dai <adaiatXYZxyz.ucar.edu>
Subject: Re: Fwd: News about GPCC
X-Spam-Score: 1.3
X-Spam-Level: +
Dear Phil et al.:
Based on my reading of their tech, report, GPCC is still gridding the total
monthly precipitation amounts
instead of anomalies. Many people (e.g., Jones and Hulme 1996; Chen et al.
2002) have shown that
it is much better to grid the anomalies besides different gridding methods,
even for temperature.
GPCC argues that gridding monthly anomalies is better for some regions but
worse for other regions,
which I can not understand.
Because of this griding method, one can not use their version 3 full data
product for assessing climate
changes (because addition or removal of wet/dry stations will have large
impacts on regional estimates
of precipitation), while their version with fixed stations (9343, but still
10% of the years may have missing
data) does not make full use of the available data. For example Chen et al.
(2002) and GHCHv2 use more than
10,000 gauges from 1948-around 1993 (over 15,000 during the 1960s and
1970s). I strongly recommend GPCC
to grid anomalies using all available gauge data for each month. Maybe they
can listen to people like Phil?
There appears to be large differences among various estiamtes for global
(land) precipitation for the last
several years (1997-present), partly because of limited number of raingages
available. The attached figure
compares land precip during 1979-2002 from Chen et al. (2002), CRU (New et
al., Mitchell et al.) and GPCP v2
(Adler et al. 2003, with climatological corrections for wind-induced
undercatch). I think it would be useful to
add both the Chen et al. (1948-present) and the new GPCC (1951-2000, the
fixed station version) analyses
into the precip plots of IPCC chapter 3.
Regards,
Aiguo Dai
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
----------------------------------------------------------------------------

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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