Cross-Calibrating Satellite Microwave Sounders and the Influence of the Diurnal Cycle

Temperature sounding microwave radiometers flown on polar-orbiting weather satellites provide a long-term, global-scale record of upper-atmosphere temperatures, beginning in late 1978 and continuing to the present.  Most of the microwave sounders have flown on satellites with orbits that drift in local measurements time.  In order to construct accurate long-term data records useful for climate-change analysis, the effects of these drifts need to be characterized and removed.  Previous versions of this dataset have used general circulation model output to remove the effects of drifting local measurement time on the measured temperatures.  Here we present a method to optimize these adjustments using information from the satellite measurements themselves, and then apply the method to help construct both climate data records of both middle tropospheric and lower tropospheric temperature.  The new method results in substantially improved agreement between measurements made by different satellites at the same time, and also results in increased global-scale warming relative to previous versions of the dataset, particularly after 1998.  We also show that the new dataset is consistent with long-term changes in total column water vapor over the oceans, and compare our results to other sources of upper air temperature data.