Speaker
Description
Variations in water vapor and other constituents in the upper troposphere and lower stratosphere (UTLS) have important radiative and chemical impacts on climate. Here we use gridded data from Aura Microwave Limb Sounder (MLS) satellite observations and five meteorological and composition-focused reanalyses (ERA5, MERRA-2, JRA-3Q, M2-SCREAM, and CAMSRA) to evaluate reanalysis representations of the mean state of water vapor, ozone, carbon monoxide (CO), and dynamical and thermodynamic fields in the tropopause layer (147–68 hPa) above the Asian summer monsoon (ASM) during the warm seasons (May–September) of 2005–2021. All reanalyses largely capture the climatological distributions and seasonal cycles of water vapor, but with systematic moist biases relative to Aura MLS. Among the five reanalyses evaluated here, M2-SCREAM (which assimilates Aura MLS) and JRA-3Q are in best agreement with Aura MLS for total water vapor; however, good quantitative agreement between JRA-3Q and Aura MLS masks compensating biases between different levels and a different seasonal cycle near the tropopause. We further describe three leading modes of deseasonalized water vapor variability in the tropopause layer (147–68 hPa) above the Asian summer monsoon (ASM). The first mode, which consists of regional-scale moist or dry anomalies on the interannual scale, is decomposed into a linear trend over 2005–2021 and detrended interannual variability. Despite strong agreement among the reanalysis products, the spatial pattern and sign of the linear trend in tropopause-layer water vapor over this period differ between Aura MLS and the reanalyses and we view the reanalysis-based trend with skepticism. Signatures of interannual variability are otherwise largely consistent, with detrended interannual variability in water vapor attributable mainly to the pre-monsoon influence of the quasi-biennial oscillation. The second mode features dry or moist anomalies centered in the northeastern and southwestern quadrants of the anticyclone coupled with weaker opposing anomalies in the southeast, while the third mode features a horizontal dipole oriented east-to-west. The second and third modes vary on subseasonal scales and often occur in quadrature, representing the propagation of quasi-biweekly waves across the monsoon domain. Although questions remain regarding the linear trend, mean biases, and a lack of direct data assimilation constraints, the overall consistency between Aura MLS and reanalysis-derived modes of variability in UTLS water vapor in this region is a promising sign that reanalyses are increasingly able to capture the processes controlling water vapor near the tropopause.
| You plan to attend | Online (MS Teams) |
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