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May21-09, 02:46 AM
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Quote Quote by joelupchurch View Post
Dr. Roy Spencer, who does the UAH, points out a few reasons for differences between UAH and RSS numbers in his blog:

The most important I think is that UAH goes down to 84S, while RSS only goes to 70S, so there can be significant differences because of Antarctic conditions.
The largest differences, by far, are in the tropics.

Another curious issue is a strong annual (seasonal) signal which starts from about 1992, in the DIFFERENCE between RSS and UAH records. It is very marked, and a number of people (including a few amateur enthusiasts who like to play with datasets!) have identified this as an issue. The most credible reason for this, I guess, is that one of the satellites has a calibration issue that varies on an annual basis. We know they have such errors already. The issue will be getting the corrections accurate enough. Someone may have over or under corrected one of the satellites. The problem has not been identified as yet, and until it is you can't tell whether it is the RSS or the UAH dataset that is most distorted by the error!

For now, we should note that the troposphere record is very much unfinished business. Stay tuned. People are looking hard for the problem. It will probably get sorted eventually.

I've been meaning to post a longer discussion of the sources of errors in satellites and surface records. It's a huge topic with a massive associated literature. (And most definitely all the issues have been known and documented and considered long before Alan Watts ever came along.)

There's one point on this which is very interesting on a personal level...

Dr Christy is a odd case, and Dr Spencer an even odder one. For onlookers, it is all too easy to classify these guys as denialists and ignore them, or (for the other side of the debate) to hold them up as the experts who will overthrow the IPCC.

My own views on that completely aside, I have been most interested to see how closely and constructively the RSS and UAH teams work together, despite being rivals. Each group has helped in finding errors in the work of the other, and as far as I can see each group actively solicits constructive criticism from the other. I'm going to post more on the whole matter of errors in the satellite record, but in the meantime... people like us here are not going to be able to give a conclusive resolution. The scientists don't have a resolution. The differences between UAH, and RSS, and the radiosondes, is all up in the air.

As I noted previously, the errors and uncertainties are much MUCH greater with the satellite data than the surface data -- even including all the horrible surface station siting issues. Explaining that is what I am hoping to tackle in another post.

When the problems with satellites are solved to the extent that people know why RSS and UAH have different trends, especially in the tropics, I expect there will be mutual recognition... just as there has been mutual recognition of some really embarrassing errors in the past. And still each group appears to hold the other in high regard for technical competence.

It's a good example of how scientists can put aside larger differences when they are hard at work on a specific empirical question. Why are RSS and UAH numbers so different? We don't know.

Cheers -- sylas

Postscript. I looked at the blog. The point #3 is significant. One of the satellites has a substantial decay in the orbit (and the RSS guys also talk about this!). RSS uses it, with corrections. UAH doesn't use it. This would explain a seasonal effect in the differences between the datasets. If this is the cause of the seasonal signal in differences, then the question becomes... does the RSS dataset get additional overall accuracy from using corrected data?