Wednesday, February 03, 2016

Those Arbitrary Changes to UAH's Model

Am I really the only one who is stunned by what Roy Spencer wrote on his blog yesterday?
"We had been concerned that the LT temperature trends over land were too warm compared to the ocean. One hint that something might be wrong was that the trends over very high elevation portions of the Greenland ice sheet and the Himalayas were much colder than the surrounding regions (see Fig. 4 here). Another was discontinuities in the trend patterns between land and ocean, especially in the tropics.

"We determined this is most likely due to a residual mismatch between the MSU channel 2 weighting function altitude on the early satellites versus the AMSU channel 5 weighting function altitude on the later satellites. We already knew AMSU5 peaks lower than MSU2, and had chosen Earth incidence angles in each to get a match based upon theory. But apparently the theory has some error, which we find equates to about 150 meters in altitude. This was enough to cause the issues we see….land too warm at low elevations, too cold for elevated ice surfaces.

“We therefore changed the AMSU5 reference Earth incidence angle (from 35.0 to 38.3 deg.) so that the trends over Greenland and the Himalayas were in much better agreement with the surrounding areas.”
(Emphasis mine.) Changing model parameters by hand to eyeball it towards a predetermined goal? What the hell....?


George Montgomery said...

Could it be that processing the UAH data is an art and has more in common with the principles of haruspicy than science?

David in Cal said...

I do not have the background to understand what Spencer's explanation means. He also wrote:

The net result is to generally cool the land trends and warm the ocean trends. The global trends have almost no change from beta4; the change mostly affects how the average trend in 2.5 deg. latitude bands is ‘apportioned’ between land and ocean.

I'm a suspicious person. I'd like to see numbers demonstrating that Spencer's change didn't significantly lower the trend.


Dano said...

David in Cal:

Remember, AFAICT all UAH updates in the past had to be corrected. This new, unpublished V 6.X will likely go thru as many revisions as necessary to get a stable, sniff-testable output. Add this to the fact Spencer was harping on the quality of the sensors, and the sniff test is fishy.



Unknown said...

I couldn't find anything directly to do with AMSU, but there is a nice clear graphic of satellite beam modes here which I guess is comparable. It suggests to me that the effect of changing from 35 to 38.3 degrees will be to include a little more data from the high troposphere and possibly lower stratosphere. Does that sound right to you, David?