An assessment of the diurnal variation of upper tropospheric humidity in reanalysis data sets

Abstract

AbstractDiurnal variations of upper tropospheric humidity (UTH) in five different reanalysis data sets are compared over convective land and ocean regions and evaluated using multiple satellite observations as a reference. All reanalysis data sets reproduce the day‐night contrast of upper tropospheric humidity and the land‐ocean contrast in the diurnal amplitude. The infrared satellite measurements indicate a slightly later diurnal minimum over land relative to most reanalyses and the microwave satellite measurements, suggesting that cloud masking of the infrared radiances may introduce a small (∼3 h) bias in the phase. One reanalysis exhibits a substantially different diurnal cycle over land which is inconsistent with both infrared and microwave satellite measurements and other reanalysis products. This product also exhibits a different covariance between vertical velocity, cloud water, and humidity than other reanalyses, suggesting that the phase bias is related to deficiencies in the parameterization of moist convective processes.