The SPARC water vapor assessment II: Assessment of satellite measurements of upper tropospheric water vapor

The figure shows a summary of the comparison of upper tropospheric humidity, provided by satellite instruments, to balloon-borne frost point hygrometers and radio sondes (no hatching), inter-satellite comparisons on basis of coincident measurements (top left to bottom right hatching), and inter-satellite comparisons on basis of zonal mean maps (hatching from top right to bottom left). The center of the bar is the mean bias relative to the balloon-borne frost point hygrometers in case of the sonde comparisons, while the width is the 1-sigma spread of the values among the sonde sites used in this study. The direct satellite-to-satellite coincidence comparisons use MLS-Aura, MIPAS-ESA, and MIPAS-IMK as the x-axis reference instrument. Exceptions are MAESTRO, which uses ACE-FTS and MLS-Aura for the reference instruments, and MLS-UARS, which uses SAGE-II. For the gridded map comparisons, MLS-Aura is used for the reference instrument in all cases except for assessing MLS-Aura itself. In that case AIRS is the reference instrument. The upper part of the figure refers to the pressure range of 200 to 140 hPa, while the lower part refers to 300 to 200 hPa. This work has been published in AMT.

Within the SPARC Water vapour assessment II (WAVAS-II) activity, upper tropospheric humidity (UTH) provided by a suite of satellite instruments has been compared to balloon-borne frost point hygrometers, Vaisala RS92 radio sondes (for pressures > 200 hPa), and among each other by multi-month mapped comparisons, zonal mean time series comparisons, and coincident satellite-to-satellite comparisons (Read et al., 2022).The tasks was complicated due to the extremely high variability of water vapour in the upper troposphere, even on small scales. In summary, most satellite data sets reviewed here show on average about 30% agreement amongst themselves and frost-point data but with an additional ~30% variability about the mean bias.