Thursday, February 2, 2012

Visualizing 2011 temperature anomalies

Jim Hansen and GISS coauthors have posted an analysis of surface temperatures through 2011. They have many GISS-style plots of months, seasons etc. Tamino has also posted a roundup.

I'm presenting here a visualization in the style I did for trends, and also for the November readings (more details on methods in those links). It shows GHCN V3 unadjusted station (and ERSST) anomalies for each month on a spherical projection, with mesh shading to show the anomalies. There's no grid averaging; the color for the anomaly of each station is shown. You can choose any combination of months, and it will show the average. You can orient the globe, zoom, display station data etc.

I calculated the anomalies using the TempLS offsets for the period 1951-2011. The base period is not exactly comparable to that for GISS etc, as the offsets are computed taking account of trend, and so should be fairly independent of the base time period. I'll describe below the treatment of missing data.

So here is the plot. The little map on top right is the navigator - click to mark the point you want to appear in the centre of the spherical projection. You can choose any combination of months - if you choose none, it will calculate the annual average. Whenever you want to change this choice, you must press Recalc (button above). You can zoom, and ask to see stations or mesh; to make these effective, press the Refresh button.

You can click on the main plot, and the anomaly for the nearest station will be printed on the right.

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Click on this map to orient the world plot.

Show Stations
Show Mesh
Jan Feb Mar
Apr May Jun
Jul Aug Sep
Oct Nov Dec

Missing data

One reason why I did not post this sooner is that GHCN info trickles in, and there is still quite a lot missing for December, and for some stations a few gaps in the year. I also had to do something about another problem - many ocean sites report -1.8%deg;C when they are frozen. This is uninformative, and does not represent the air temperature, so I regarded it as missing data.

I can't modify the mesh easily in Javascript, so I really have to use the same mesh for each month whether data is missing or not. So the rule I used was that stations with less than nine months of informative data were omitted. Otherwise missing values were set to zero anomaly. There are a few of these in December, particularly. If you see an outlier color, check its anomaly by clicking. If it's zero, it's probably a missing data point.