Subject: [Fwd: Re: HadCRUT2v]
Date: Tue, 13 Dec 2005 21:14:30 -0000 (GMT)
Cc: firstname.lastname@example.org, email@example.com
There seems to be a problem with the South Pole
box (#2592). The data are in CRUTEM2(v) but not in
HadCRUT2(v). See the plot and email from Tim Osborn.
Email Tim if you can find what is up. The boxes in
the two datasets should be the same.
I'm in NZ at IPCC.
---------------------------- Original Message ----------------------------
Subject: Re: HadCRUT2v
From: "Tim Osborn" <firstname.lastname@example.org>
Date: Tue, December 13, 2005 1:07 pm
"Tom Wigley" <email@example.com>
Cc: "Ben Santer" <firstname.lastname@example.org>
attached is a plot of the monthly anomalies from the only box with
non-missing data in the bottom row of Phil's grid (centred at 87.5
S). This is from HadCRUT2v that I picked up from the CRU data store
in June this year.
Clearly the dates Tom listed are missing in my version
too. Furthermore, the values from 1971-1975 are abnormal. They are
not all identical, but are all near zero. Perhaps multiplied by 0.1?
Similar problems are apparent in HadCRUT and CRUTEM2v too.
But CRUTEM2 has no gaps and no abnormal periods at the South Pole, so
perhaps CRUTEM2 is fine? Tom - if it's urgent, you could extract the
South Pole time series from CRUTEM2 and use it to overwrite the other
3 data sets until Phil corrects them.
Regarding the weighting issue...
Given that the grid doesn't have equal-area boxes, there are always
going to be compromises with weighting. Even if you do something to
sort out the problem at the S. Pole, how about the isolated boxes
around the coast of Antarctica, which will be given much less weight
than an isolated box in the tropics which might also have only 1
station in. This is partly reasonable because of differences in
spatial correlation of temperatures between tropics and high
latitudes, but I'm sure that they don't compensate exactly.
Specifically for the poles...
Putting the temperature data into a single box will clearly
underweight its contribution in area averages (is it significant from
a practical point of view once you get to hemispheric or global
Replicating it into all boxes in the bottom row will, on the other
hand, gives it too much weight. If the area weighting is calculated
simply as cos(latitude) then the South Pole data will be given this
72*cos(87.5) = 3.14
whereas one box on the equator (or just off) will be given this weighting:
1*cos(2.5) = 1.00
so, if replicated around all boxes at 87.5 S, the South Pole would
have three times the weight of a single tropical box (compared with
23 times less weight if South Pole data appears in only one box).
Perhaps put it in every fourth box, giving a weighting of 0.79 (bit
less than tropical, which is reasonable for spatial correlation reasons)?
At 04:11 13/12/2005, P.Jones@uea.ac.uk wrote:
> In NZ at the IPCC meeting. Will be here until Dec 17.
> When I get back I'm off to Switzerland for Christmas on
> Dec 21.
> The South Pole shouldn't be missing. I have all the
> data for Amundsen-Scott from 1957. I put the data in at
> one 5 degree grid box, so it doesn't get overweighted.
> The South Pole should be at the last grid box (2592)
> in the 72 by 36 array. Putting the data in all 87.5-90S
> boxes would overweight the S.Pole stations.
> There isn't any data at the N. Pole.
> Maybe Tim could check on the missing S.Pole data.
> I reckon it should be there in all the datasets CRUTEM2
> and HadCRUT2 and the v versions.
> > Phil,
> > Why is there so much missing data for the South Pole? The period Jan 75
> > thru
> > Dec 90 is all missing except Dec 81, July & Dec 85, Apr 87, Apr & Sept
> > Apr 89. Also, from and including Aug 2003 is missing.
> > Also -- more seriously but correctable. The S Pole is just represented
> > by a single
> > box at 87.5S (N Pole ditto I suspect). This screws up area averaging. It
> > would be
> > better to put the S Pole value in ALL boxes at 87.5S.
> > I have had to do this in my code -- but you really should fix the 'raw'
> > gridded data.
> > For area averages, the difference is between having the S Pole represent
> > the whole
> > region south of 85S, and having (as now) it represent one 72nd of this
> > region. It
> > is pretty obvious to me what is better.
> > This affects the impression of missing data too of course.
> > Tom.
Dr Timothy J Osborn
Climatic Research Unit
School of Environmental Sciences, University of East Anglia
Norwich NR4 7TJ, UK
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