Changes in Upper Troposphere/Lower Stratosphere Aerosol Since 1980 in the Goddard Earth Observing System (GEOS-5) Model

Abstract:

Most aerosol enter the UTLS through tropical upwelling. In the last 6 years, however, new analyses of satellite observations have identified a region of enhanced aerosol extinction in the UTLS above Asia during the summertime. This enhancement, called the Asian Tropopause Aerosol Layer (ATAL), is connected to the Asian monsoon convective system, which transports pollutants and aerosols across the tropopause from the troposphere. While the specific composition of the ATAL is not well quantified, the few in-situ measurements available suggest that carbonaceous aerosol contribute significantly to the ATAL. Its sources and the anthropogenic contribution are also not well known. The ATAL is visible in observations since the late 1990s: the appearing of the ATAL in the late 1990s could be related to the sudden increase in Asian emissions (if they are indeed a major contributor to ATAL), or it might have simply been masked by the aerosol from the Mt. Pinatubo eruption in the years prior.

In this talk we will show changes in extinction and composition of UTLS aerosol in high resolution simulations performed with the NASA Goddard Earth System Model (GEOS-5) from 1980 to 2016. In particular, we will analyze the MERRA-2 reanalysis, which includes the assimilation of aerosol extinction, and the MERRA2-GMI replay simulation, a new publicly available GEOS-5 simulation driven by the MERRA-2 reanalysis and including full stratospheric and tropospheric chemistry, but not aerosol assimilation.