Evaluating the Absolute Calibration Accuracy and Stability of AIRS using the CMC SST

We compare the daily mean and standard deviation of the difference between the Sea Surface skin Temperature (SST) derived from clear Atmospheric InfraRed Sounder (AIRS) data from seven atmospheric window channels between 2002 and 2020 and collocated Canadian Meteorological Centre (CMC) SST data from the tropical oceans. After correcting the mean difference for cloud contamination and diurnal effects, the remaining bias relative to the CMC SST, is not inconsistent with estimates of the AIRS absolute accuracy based on the uncertainty of the pre-launch calibration. The time series of the bias produces trends well below the 10 mK/yr level required for climate change evaluations. The trends are in the 2 mK/yr range for the five window channels between 790 and 1231 cm-1, and +5 mK/yr for the shortwave channels. Between 2002 and 2020 the time series of the standard deviation of the difference between the AIRS SST and the CMC SST shows the effects of version changes in the CMC SST, but dropped fairly steadily to below 0.4 K in several AIRS window channels, a level previously only seen in SST models relative to the Argo buoys.