An assessment of the consistency between satellite measurements of upper tropospheric water vapor

We assess the consistency of the satellite-based observations of upper tropospheric water vapor (UTWV) by comparing brightness temperature measurements from the channel 12 of High-Resolution Infrared Radiation Sounder (HIRS), the 183.311GHz channel of Advanced Microwave Sounding Unit-B (AMSU-B)/Microwave Humidity Sounder (MHS), and spectral radiances from the Atmospheric Infrared Sounder (AIRS). All three products exhibit consistent spatial and temporal patterns of interannual variability. On decadal time scales, the spatial patterns of trends are similar between all three products; however, the amplitude of the regional trends is noticeably weaker in the HIRS measurements than in either the AMSU-B/MHS or AIRS data. This presumably reflects the greater clear-sky sampling limitations of HIRS relative to the other products. However, when averaged over tropical or near-global spatial scales, the trends between all three products are statistically indistinguishable from each other. The overall consistency between all three products provides important verification of their credibility for documenting long-term changes in UTWV. A similar analysis is performed for reanalysis-produced and model-simulated UTWV using the HIRS record as a benchmark. On decadal time scales, both reanalysis data sets and the multimodel ensemble mean have difficulty in capturing the observed moistening of climatologically dry regions of the subtropics, although the model-simulated trends are more consistent with the HIRS measurements than the reanalysis data.