UTLS Transport by Asian Summer Monsoon: A Model Investigation and Hypotheses for In Situ Observations

Abstract:

Asian Summer Monsoon (ASM) system is shown by satellite observations to be a significant driver in transport between the boundary layer and the upper troposphere/lower stratosphere (UT/LS). Satellite observations, although capturing the global impact on seasonal scales, are unable to resolve the details of the transport process. To investigate the interplay of convection and the large-scale monsoonal circulation in UT/LS transport, we analyzed the tracer behavior in the ASM region using NCAR Whole Atmosphere Community Climate Model run in specified dynamics mode (WACCM-SD). Dynamical variability of the carbon monoxide, a tracer of tropospheric pollutants and their relationship with the tropopause are examined in association with the sub-seasonal variability of the anticyclone. The results show that monsoon convection creates a “bubble” of tropospheric air above the mean tropopause in the ASM region. The intra-seasonal oscillation at the UT/LS level plays an essential role in transporting convectively pumped boundary layer pollutants into the stratosphere. Our analysis also shows that there is a preferred location for the uplifted boundary layer to reach the tropopause level. Airborne in situ observations may be an essential tool to verify these model results.