Sunday, October 11, 2015

TempLS September and Antarctica

I wrote last about possible reasons for the drop in temperature in September shown by TempLS mesh, contreasted with the stasis shown by the grid weighting, and the rise shown by the NCEP/NCAR index. I thought that it was due to the large negative contribution assigned by mesh to Antarctica, wish has low weighting in grid.

I should have remembered that a while ago I reported that the WebGL shaded map of station temperatures is now updated daily, and is actually a better guide to what is reporting than the map of dots that I show in the daily TempLS report. I upgraded the WebGL to now show, on request, the mesh as well as the stations. That makes clearer what is happening in Antarctica, and what is reporting.

So here is a snapshot of what it reports for September, compared with August:

August 2015September 2015

You can check the original for color scale. It shows that in September, both the land of Antarctica (mostly) and much of the adjacent sea were cold, remembering that there is a lot of sea ice as well. In August, it varied more between cold and normal. But also, it shows that basically all the Antarctic reports for September are in.

So it shows why a few Antarctic stations in the mesh version carry high weight. The weight is the area of the adjacent triangles. The weighted sum of the land stations brings down the month average by about 0.1°C. But parts of the sea are very cold too, and they can also have large triangles attached. Generally, the ocean has a regular mesh, and approx equal weighting. These weighted cold parts bring down the average relative to the grid version, which doesn't have that heavy weighting.

So, you may ask, is the mesh version wrong? I don't think so. The Antarctic results are uncertain. The grid version infills much of the area with global average values. This is conservative from a noise point of view, but hard to justify as a good estimate. The mesh version gives about as good an estimate as you can get, but is necessarily sensitive to a small base of data.

I think the WebGL mesh plot should really replace the dot picture and also the rectangular shaded plot. It's hard to compare directly with GISS, though, and is a bit data-heavy for loading. I'll try to work out what is best.


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