Cooler sea surface west of the Sahara Desert correlated to dust events

Abstract

Atmospheric particles scatter incoming solar radiation and cause regional cooling for areas in which they increase the net backscattering. Stratospheric aerosols have been widely observed to have this cooling effect on the Earth's surface following major volcanic eruptions. A smaller effect is expected to result from the regular entrainment of aerosols in the troposphere from natural and anthropogenic surface sources. Over long time scales, even a small cooling by tropospheric aerosols could be significant in offsetting warming caused by greenhouse gases. We looked for indications of this effect at the ocean's surface, when the albedo is raised in the presence of tropospheric aerosols. To test whether a correlation exists between tropospheric aerosol outbreaks and a cooler ocean surface, we compared satelalite-derived aerosol optical depth (AOD) measurements to in situ sea surface temperatures (SSTs) over a four year period. We seolected a subtropical North Atlantic region where the upwind mobilization of desert dust results in an aerosol signal large enough to outweigh other factors which cause cooling of the sea surface. In this location, the differing seasonal variations of aerosol amount, mixed layer depth, and cloudiness permit a glimpse of the causal relationship between aerosols and temperature changes at the sea surface. Although we were limited by in situ SST coverage, we found temperature perturbations correlated to large aerosol outbreaks from the Sahara Desert.