Friday, May 25, 2012


date: Tue Mar 2 09:10:15 2004
from: Phil Jones <>
subject: Re: [Fwd: Re: More PCM-ERA40 comparisons]
to: Ben Santer <>,

Dear Ben and Adrian,
All these sorts of comparisons are useful. It is important that we do them rather some
of the people in the skeptic camp - as we'll do them properly. Importance is there with
IPCC AR4 coming along.
Also, I hope the importance of the synops to the Reanalysis will lead to more
being made available to get the basic input data in good shape for 3rd generation runs
of Reanalysis, and also to improvements to the models as well.
At 18:44 01/03/2004 -0800, Ben Santer wrote:

Dear Adrian,
Thanks very much - your paper on the ERA-40/CRU comparisons will be very useful
to the PCM group (Warren Washington, Jerry Meehl, Tom Wigley, Caspar Ammann, and
Julie Arblaster). It might also be helpful for Phil Jones to see a copy of our
joint Nature paper, since you mention this in the ERA-40/CRU comparisons. I'll
forward a copy of the Nature paper to Phil. I'll also send Phil the figures with
the 2m temperature changes in PCM and ERA-40.
I'll be away at the Goddard Space Flight Center for a few days, but should be
back in my office on Friday.
With best regards,

Adrian Simmons wrote:
> Ben
> Further to the response below I've no problem with you passing the draft
> on the ERA-40/CRU comparisons on to your other potential collaborators
> in this work.
> Adrian
> -------- Original Message --------
> Subject: Re: More PCM-ERA40 comparisons
> Date: Fri, 27 Feb 2004 08:39:05 +0000
> From: Adrian Simmons <>
> Reply-To:
> Organization: ECMWF
> To: Ben Santer <>
> References: <> <>
> Ben
> Very interesting, particularly as we have reason from the comparison
> with CRU data to think that ERA-40 in general has a warm bias in
> two-metre temperature in the early years.
> I'd certainly like to kep in touch with you on this, and we can regard
> it as collaboration if I contribute something material. As you will have
> seen from the email that accompanied the ERA-40/CRU results I've been
> liaising with Phil Jones over them. It's too early to say in what form
> we submit the results to the open literature, but I'm keen to at least
> get them out quite quickly as an ERA-40 report.
> No more definite news on my May trip yet.
> Best regards
> Adrian
> Ben Santer wrote:
> > Dear Adrian,
> >
> > Thanks very much for sending me your comparison of surface air temperature
> > changes in CRU and ERA-40. I've been looking at a related issue - the
> > correspondence between 2m temperature changes in ERA-40 and PCM.
> >
> > Here's the background to this work. Increasingly, there is some interest in the
> > problem of identifying anthropogenic climate change at regional scales. I have
> > to give a brief talk on this subject tomorrow. In preparing for this talk, I
> > decided that it would be useful to show how signal and noise change as a
> > function of spatial scale. I looked at the behavior of 2m temperature in the
> > four individual realizations of the PCM "ALL forcings" experiment (the same
> > experiment that we analysed in our joint Nature paper). For each realization, I
> > computed spatial averages over the globe, the Northern Hemisphere, and the
> > western United States (30-50N, 126W-114W). These spatial averages were then
> > expressed as anomalies relative to climatological monthly means over 1979-1999.
> > The orange shading in the three panels of the figure entitled ""
> > is a measure of the between-realization variability in PCM. The envelope is
> > simply the range (during any given month) between the maximum and minimum values
> > of the four realizations. This range was then low-pass filtered. The solid red
> > is the low-pass filtered ensemble mean.
> >
> > To facilitate comparison with PCM data, I've defined 2m temperature anomalies in
> > ERA-40 in the same way (i.e., relative to climatological monthly means over
> > 1979-1999), and have used the same low-pass filter. One can then ask whether the
> > 2m temperature changes in ERA-40 are consistent with those in PCM - in other
> > words, are they encompassed by PCM's envelope of possible climate responses to
> > combined anthropogenic and natural forcing?
> >
> > They are. Surprisingly, this consistency occurs not only at the global-mean
> > level, but also for the NH and western U.S. For the global-mean and the NH, the
> > ERA-40 2m temperature changes are outside PCM's envelope of 2m temperature
> > changes during the first 5-10 years of the reanalysis. After the late 1960s,
> > however, the ERA-40 2m temperature changes are entirely consistent with those in
> > PCM. Over the western U.S., 2m temperature changes in PCM and ERA-40 are
> > consistent throughout the reanalysis period.
> >
> > Such qualitative consistency, while interesting, is no substitute for formal,
> > pattern-based fingerprint detection studies at global, hemispheric, and regional
> > scales. For example, an overestimate of the regional-scale variability of 2m
> > temperature by PCM could explain why PCM's 2m temperature changes over the
> > western U.S. fully encompass the ERA-40 result (see panel C). On the other hand,
> > there is some real similarity in the low-frequency component of the 2m
> > temperature changes in ERA-40 and PCM (look at the similar responses to Agung,
> > Chichon, and Pinatubo in panel B!)
> >
> > The bottom line is that PCM's 2m temperature changes are reasonably consistent
> > with those in ERA-40, even at sub-global spatial scales. This suggests that
> > formal regional-scale detection work might be useful. If you are interested,
> > perhaps we could collaborate on such work. A collaboration would also involve
> > the PCM group at NCAR (to whom I'm copying this email).
> >
> > The second figure that I've appended shows the global-mean changes in synthetic
> > MSU channel 2 temperatures in PCM and ERA-40. The message is pretty much the
> > same as for 2m temperatures: PCM's "envelope" of possible changes in
> > tropospheric temperatures largely encompasses the ERA-40 results, except during
> > a few large El Nino and La Nina events. Once again, there is surprising
> > similarity in the low-frequency component of the model and reanalysis T2
> > changes.
> >
> > It would be fun to take these simple comparisons a little further!
> >
> > With best regards,
> >
> > Ben
> --
> --------------------------------------------------
> 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
> --------------------------------------------------
> --
> --------------------------------------------------
> 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
> --------------------------------------------------
Benjamin D. Santer
Program for Climate Model Diagnosis and Intercomparison
Lawrence Livermore National Laboratory
P.O. Box 808, Mail Stop L-103
Livermore, CA 94550, U.S.A.
Tel: (925) 422-7638
FAX: (925) 422-7675

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

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