Saturday, June 2, 2012


cc: Phil Jones <>, Kate Willett <>, Dick Dee <>,
date: Fri, 30 Jan 2009 10:41:06 +0000
from: "peter.thorne" <>
subject: Re: CRUTEM3v and HadCRUH comparisons with ERA-40 and ERA-Interim
to: Adrain Simmons <>

Hi Adrian et al.,

thanks for the update. Looks good. Very interesting stuff.

I'm including Dave Levinson in here to speak to the precip issue in my
very last point. I knew there had to be some benefit to my being chapter
lead in the BAMS State of the Climate report. Dave did the precip
analysis for AR4 or at least can get hold of the different datasets.

Okay, on with comments:

trying to head off likely reviewer concerns in tables 1 and 2 is quoting
to 4 s.f. scientifically justified given the likely errors that are
involved in both the obs datasets and the reanalyses? Would 2 or at most
3 s.f be more rational? Is a difference in the 3rd or 4th s.f.
meaningful and pointing to a real difference that we should be
investigating or simply an artifact of inclusion / exclusion of one or
two datapoints?

I like the plotting style in Fig 1., can this be replicated in Figure 6
so we are internally consistent?

I'd still like to see an assessment of the significance of differences
when we compare obs and rean timeseries (various places) in a formal
sense. Maybe this is in the text but not the Figures in which case
please move on move on, nothing to see officer. Otherwise I just feel
that this protects us from an obvious angle of attack by the usual
suspects if this thing gets picked up and turned over by climatefraudit
or associates. Saying its statistically indistinguishable also bolsters
the scientific value of the analysis substantially in my view.

I'm intrigued by what is going on in sub-saharan Africa ERA-INT in Fig.
3. Do we have any confidence in this feature? It kind of jumps out at
you so may be worth addressing / discussing.

Figure 11 and associated discussion seems a reasonable strawman to me.
What does the rean soil moisture do as that is the local source over
land. Do we see large-scale drying? Pity we don't have a reasonable soil
moisture obs dataset. I think in the rean at least we have access to
enough variables to actually corroborate the strawman even if we cannot
then confirm it in the real-world because of a lack of data ...!

In figure 12 you use GPCP data. Now precip estimates over land are
highly uncertain, and differ substantially on multi-decadal timescales.
So I'd be loathed to rely upon a single dataset version to make a
meaningful conclusion about the differences between obs and rean. 1999
would fit rather well with ATOVS introduction and that may help explain
any apparent jump. But equally plausibly GPCP may be in error. I'd at
least use the NCDC GHCN dataset and possibly others here to be totally
sure that we are attributing the problem to the right cause (rean or


Peter Thorne Climate Research Scientist
Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB
tel. +44 1392 886552 fax +44 1392 885681

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