September UAH is out….or is it?

September UAH is out, but as Roy Spencer says we have a we problem.

Looks like we might have to wait a while for an accurate measure, in his post here its explained more clearly.

UAH V5.5 Global Temp. Update for Sept. 2012: +0.34 deg. C

October 5th, 2012 by Roy W. Spencer, Ph. D.

As discussed in my post from yesterday, the spurious warming in Aqua AMSU channel 5 has resulted in the need for revisions to the UAH global lower tropospheric temperature (LT) product.

Rather than issuing an early release of Version 6, which has been in the works for about a year now, we decided to do something simpler: remove Aqua AMSU after a certain date, and replace it with the average of NOAA-15 and NOAA-18 AMSU data. Even though the two NOAA satellites have experienced diurnal drifts in their orbits, we have found that those drifts are in opposite directions and approximately cancel. (The drifts will be corrected for in Version 6.0).

The new interim dataset, Version 5.5, has a September, 2012 global lower tropospheric temperature anomaly of +0.34 deg. C (click for large version): Note that the new v5.5 dataset brings our monthly anomalies over the last few years somewhat more in line with those from RSS, which have been running significantly cooler than ours. The trend change from v5.4 to v5.5, however, only decreases by 0.001 deg. C/decade. This is partly because the time series is now almost 34 years in length, and adjusting the last several months by 0.1 deg or so is not going to affect the long-term trend substantially.

Evidence of the divergence of Aqua from the two NOAA satellites during 2012 is shown in the next plot:

The global monthly differences between v5.5 and v5.4 are shown next, which reveals the rapid divergence in the last couple months of Aqua AMSU from the average of NOAA-15 1nad NOAA-18 AMSUs:

Again, Version 5.5 is only meant as an interim solution until our Version 6 is ready, which has new corrections for diurnal drift and an improved calibration strategy for the old MSU instruments.

Our reluctance to make these changes sooner is partly due to the flak we get when we are accused of adjusting temperatures downward for no good reason. There is now sufficient evidence (alluded to above) to make such adjustments.


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