Diverse Effects of Aerosol Forcing Distribution and Magnitude on Tropical Zonal Circulation

Anthropogenic aerosols have a considerable impact on the radiative balance of the Earth and are believed to contribute to a cooling of the climate. However, in contrast to long lived greenhouse gases, aerosols and their radiative forcing display large spatial variations. This uneven radiative forcing distribution may cause changes in regional as well as global circulation patterns.

The effect of anthropogenic aerosols on the zonal tropical circulation is investigated using the global coupled climate model EC-Earth.The relatively low forcing resulting from only modeling the direct aerosol effect led to a negligible tropical mean temperature and precipitation response. Nevertheless, the aerosol direct radiative forcing had a considerable local impact on the zonal overturning circulation over the Indian Ocean. The aerosol forcing led to decrease of the most intense convective precipitation and the related pressure velocity field over the Maritime Continent. It is found that it is predominantly scattering aerosols that are responsible for these changes. When the cloud albedo effect was included, on the other hand, the tropics experienced a cooling and a subsequent precipitation reduction.

The results indicate that the uneven spatial distribution of the aerosol radiative forcing can lead to substantial local effects on the tropical zonal overturning circulation and precipitation without necessarily relying on a tropical wide cooling and a thermodynamic scaling argument. Moreover, these local aerosol induced convection and precipitation changes may in turn influence the global atmospheric circulation.