The Observed Influence of Tropical Convection on the Saharan Dust Layer

Abstract

Interactions between convection and the Saharan Air Layer in the tropical Atlantic Ocean are quantified using a novel compositing technique that leverages geostationary cloud observations to add temporal context to the polar orbiting CloudSat and the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites allowing aerosol optical depth (AOD) changes to be tracked throughout a typical convective storm life cycle. Four years of CALIPSO observations suggests that approximately 20% of the dust mass in every 10° longitude band between 10°W and 80°W is deposited into the ocean. Combining a new convective identification algorithm based on hourly geostationary cloud products with AODdust profiles along the CALIPSO track reveals that wet scavenging by convection is responsible for a significant fraction of this deposition across the Atlantic. Composites of 4 years of convective systems reveal that, on average, convection accounts for 15% ± 7% of the dust deposition in each longitude band relative to preconvective amounts, implying that dry deposition and scavenging by nonconvective events are responsible for the remaining 85% of dust removal. In addition, dust layers are detrained at upper levels of the atmosphere between 8 and 12 km by convective storms across the Atlantic. The dust budget analysis presented here indicates that convection lofts 1.5% ± 0.6% of dust aerosol mass to altitudes greater than 6 km. This may have significant implications for cloud formation downstream of convection since lofted dust particles can act as effective ice nucleating particles, altering cloud microphysical and radiative properties, latent heating, and precipitation rates.