Composition of the Asian Summer Monsoon Anticyclone: Climatology and Variability from 11 Years of Aura Microwave Limb Sounder Measurements (Invited Presentation)

The Asian summer monsoon (ASM) is characterized by persistent deep convection and a strong upper-level anticyclonic vortex that spans the region from East Asia to the Middle East. The associated rapid vertical transport strongly influences constituent distributions in the upper troposphere / lower stratosphere (UTLS), bringing up relatively moist, ozone-poor air from near the surface. The intense convection also rapidly lofts boundary layer pollutants into the UTLS, where air masses can remain confined within the closed circulation of the anticyclone for several weeks. Satellite measurements are invaluable for investigating the impact of pollution transport on the composition of the ASM anticyclone, which has been sparsely sampled by other means. The Microwave Limb Sounder (MLS), launched as part of NASA's Aura mission in July 2004, makes simultaneous co-located measurements of trace gases and cloud ice water content (IWC, a proxy for deep convection) in the UTLS on a daily basis. Here we exploit the dense spatial and temporal coverage, long-term data record, and extensive measurement suite of Aura MLS to characterize the climatological composition of the ASM anticyclone and quantify its considerable spatial, seasonal, and interannual variability. We relate the observed trace gas behavior to various meteorological quantities, such as the size and strength of the ASM anticyclone, the extent and intensity of deep convection, and variations in the tropopause and the upper tropospheric jets in that region. Comparisons with simulations from a chemistry climate model are performed to evaluate how well the model reproduces the observed trace gas distributions. Multiple species of both tropospheric and stratospheric origin are examined to help assess whether the observed variability arises from variations in transport processes or changes in the strength or location of surface emissions.