African dust outbreaks: A satellite perspective of temporal and spatial variability over the tropical Atlantic Ocean

Abstract

We describe the temporal evolution and spatial structure of extreme African dust outbreaks and their associated meteorological fields over West Africa and the tropical Atlantic using A‐Train data and a global reanalysis product. We used Aqua–Moderate Resolution Imaging Spectroradiometer daily aerosol optical depth (AOD) to identify major dust outbreaks, defined as AOD events one standard deviation above the background along the African coast. Dry air outbreaks were defined using water vapor data of the Aqua Atmospheric Infrared Sounder. Dry air outbreaks do not always coincide with dust outbreaks. Most boreal summer outbreaks reached the West Indies between 10°N and 20°N, some traveling on to the southeastern United States; winter outbreaks moved to South America between 0° and 10°N. Outbreaks travel westward at an average speed of 1000 km d−1, reaching the Caribbean or South America in a week's time. The advance of a dust front is associated with decreases in water vapor (up to −1.0 g kg−1) and increases in temperature (up to 1.0 K) and, behind the fronts, an anticyclonic circulation. We used Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data to characterize dust altitude distributions. The vertical distribution of warm dry air is similar to that of dust observed in CALIPSO. The dust layer altitude decreases during transport across the Atlantic and is significantly lower in boreal winter than summer. The study highlights the temporal and spatial variability of African dust outbreaks, which are important to improving our understanding of climate impacts of African dust and Atlantic climate variability in general.