The Role of Anthropogenic Aerosol in Tropical Expansion

Abstract:

A new tropopause definition involving a flow-dependent blending of the traditional thermal tropopause with one based on potential vorticity has been developed and applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA), ERA-Interim. Previous and new metrics for the rate of broadening of the tropics, based on both height and wind, gave trends in the range 0.9–2.2◦ per decade for 1989–2007. It was found that these changes are mainly concentrated in the eastern hemisphere.

The blended tropopause dataset has now been extended to run from 1979-2014. We examine whether the tropical expansion trends identified for 1989-2007, and the east-west asymmetry in expansion rates, are robust to the extension of the dataset. We ask whether anthropogenic aerosol might play a role in the east-west asymmetry, and use single forcing experiments from CMIP5 to quantify the role of anthropogenic aerosol in trends in tropical width.