Characterization of merged AIRS and MLS water vapor sensitivity through integration of averaging kernels and retrievals

Abstract. In this paper, we analyze averaging kernels to assess the sensitivity of the Aqua Atmospheric Infrared Sounder (AIRS) and Aura Microwave Limb Sounder (MLS) to water vapor. The averaging kernels, in the tropical and extra-tropical upper tropospheric and lower stratospheric region of the atmosphere, indicate that AIRS is primarily sensitive to water vapor concentrations typical of tropospheric values up to a level around 260 hPa. At lower pressures AIRS retrievals lose sensitivity to water vapor, though not completely as indicated by the non-zero verticalities at pressures less than 260 hPa. The MLS is able to provide high quality retrievals, with verticalities ~1 for all pressure levels, down to the same level for where AIRS begins to lose sensitivity. Previous analyses have estimated both instruments to have overlapping sensitivity to water vapor over a half temperature scale height layer, within the upper troposphere, for concentrations between ~30–400 ppmv. Thus, we implement a method using the averaging kernel information to join the AIRS and MLS profiles into an merged set of water vapor profiles. The final combined profiles are not only smooth functions with height but preserve the atmospheric state as interpreted by both the AIRS and MLS instruments.