Covariability of dynamics and composition in the Asian monsoon tropopause layer from satellite observations and reanalysis products

Abstract. We describe three leading modes of deseasonalized water vapor variability in the tropopause layer (147–68 hPa) above the Asian summer monsoon (ASM) based on Aura Microwave Limb Sounder (MLS) satellite observations and five meteorological and composition-focused reanalyses. The first mode, which describes regional-scale moist or dry anomalies on interannual scales, is separated into a linear trend and detrended interannual variability. Although the reanalysis products all show an increasing trend in tropopause-layer water vapor over 2005–2021, the spatial pattern and sign of the trend disagree between Aura MLS and the reanalyses. The regional water vapor budget indicates that the reanalysis trend originates outside the monsoon region, beyond the domain of our analysis. Interannual variability is otherwise consistent, arising mainly from the pre-monsoon influence of the quasi-biennial oscillation. The second mode features anomalies arcing from the southwestern to northeastern quadrants of the anticyclone coupled with weaker opposing anomalies in the southeast, while the third mode features a horizontal dipole oriented east-to-west. These two modes often vary in quadrature due to the influences of quasi-biweekly waves on deep convective activity, but also appear independently when other modes of convective variability manifest in similar centers of action. Although questions remain regarding the linear trend, mean biases, and the weak and possibly adverse influence of data assimilation, the consistency between Aura MLS and reanalysis-derived modes of variability in UTLS water vapor in this region shows that atmospheric reanalyses are increasingly able to capture the processes controlling water vapor near the tropopause.