So, you release a dataset that people have been clamouring for, and the buggers only start
using it! And finding problems. For instance:
Hi Tim (good start! -ed)
I realise you are likely to be very busy at the moment, but we have come across something in
the CRU TS 3.0 data set which I hope you can help out with.
We have been looking at the monthly precipitation totals over southern Africa (Angola, to be
precise), and have found some rather large differences between precipitation as specified in
the TS 2.1 data set, and the new TS 3.0 version. Specifically, April 1967 for the cell 12.75
south, 16.25 east, the monthly total in the TS 2.1 data set is 251mm, whereas in TS 3.0 it is
476mm. The anomaly does not only appear in this cell, but also in a number of neighbouring
cells. This is quite a large difference, and the new TS 3.0 value doesn't entirely tie in
with what we might have expected from the station-based precip data we have for this area.
Would it be possible for you could have a quick look into this issue?
Dr Daniel Kingston
Post Doctoral Research Associate
Department of Geography
University College London
Tel. +44 (0)20 7679 0510
Well, it's a good question! And it took over two weeks to answer. I wrote angola.m, which
pretty much established that three local stations had been augmented for 3.0, and that
April 1967 was anomalously wet. Lots of non-reporting stations (ie too few years to form
normals) also had high values. As part of this, I also wrote angola3.m, which added two
rather interesting plots: the climatology, and the output from the Fortran gridder I'd just
completed. This raised a couple of points of interest:
1. The 2.10 output doesn't look like the climatology, despite there being no stations in
the area. It ought to have simply relaxed to the clim, instead it's wetter.
2. The gridder output is lower than 3.0, and much lower than the stations!
I asked Tim and Phil about 1., they couldn't give a definitive opinion. As for 2., their
guesses were correct, I needed to mod the distance weighting. As usual, see gridder.sandpit
for the full info.