Subject: cruts tmp to 2008
Date: Fri, 10 Jul 2009 00:19:58 +0100 (BST)
Cc: "tim Osborn" <firstname.lastname@example.org>
finally had time to take a look at the latest cruts3 run through to 2008
for tmp, picked up from /cru/cruts/
Two PDFs showing seasonal national means are attached.
Look at ...2008a_vs_2008b.pdf first. Black is your previous update to
2008, pink is the latest one. Many very similar, some small differences
(presumably due to outlier 3/4 SD removal... note that as these are
national/seasonal means, outliers might be quite large, yet only show up
small in the means if many other stations contribute).
page 4. The hot spike in Guatemala SON has been removed in the new
version. That looks much better.
page 6 & page 9: the hot spikes in France, Italy and Austria in JJA in
2003 have been reduce slightly too. Not sure if this is right or not,
could ask Phil what he thinks. Could Jul & Aug 2003 have been so hot that
some observations validly did exceed the +3SD outlier check? Or do you
use a +4SD check for TMP? Anyway, this is one to ask Phil about.
There are various other erroneous hot spikes that have now been correctly
removed, I won't list them all here.
However, there are some cold spikes in both previous and latest 2008
updates... see e.g. Mali SON on page 12. Have you turned on only outlier
checking for +3SD, and not for -3SD? Some wrong-looking cold spikes are
Now look at ...2005_vs_2008b.pdf. Black is last years CRUTS3 through to
2005 (I know the files went to mid 2006, but I stopped at last complete
year). Note this isn't CRUTS2.1! :-) Pink is again the newest version of
the update to 2008.
There are some early 20th century differences that I'm not too bothered
about, though it would be nice to know why they arise. One concern is
that the mean level is different between the versions... see e.g. JJA for
various countries on pages 7 and 8. Seems to be a constant offset. It's
too big to be a simple rounding error in my calculations (I may have
changed from 1 dec. place to 2 dec. place, but some differences are about
0.5 deg C), and these are absolute values so there's no dependency on any
anomalisation/reference period meaning as I'm not doing any.
Intriguing. Perhaps some normals have change in some regions/seasons?
(1) hot spikes have been corrected.
(2) cold spikes still there.
(3) some odd differences in mean level.
Dr. Tim Osborn
RCUK Academic Fellow
Climatic Research Unit
School of Environmental Sciences
University of East Anglia
Norwich NR4 7TJ, UK
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