How has the Saharan air layer evolved with transport across the Atlantic? Observations from South Florida's Cloud-Aerosol-Rain-Observatory (CAROb)

Saharan dust is important climatically, and primarily advected westward from the African continent within warm, dry layers elevated to 1-4 km in altitude. Much of what is known about the Saharan Air Layer (SAL) is based on analysis from the eastern Atlantic, and SAL properties after long-range transport have been less examined. The most polluted conditions in South Florida occur in the summers when Saharan dust is present. A continuous dust record developed from surface-based filter sampling dates back to 1978 (Prospero et al., 1999). Since 2011, this has been augmented by measurements from a surface-based cloud condensation nuclei counter, AERONET, and a depolarization lidar at South Florida's Cloud-Aerosol-Rain-Observatory (CAROb; http://carob.rsmas.miami.edu). We use these measurements to examine the vertical structure of the Saharan dust layers that reach the United States during the summers of 2012 and 2013. In combination, the CAROb measurements allow us to 1) assess if Saharan dust has been incorporated into the boundary layer, 2) if AERONET measurements (aerosol optical depth and angstrom exponent) can serve as a proxy for surface dust deposition and possible cloud-dust interactions within the boundary layer, 3) if surface measurements are a reasonable proxy for atmospheric dust loading, and, 4) the cloud-nucleating potential of the aged dust. These results have revelance for the depiction and assessment of Saharan dust within climate models.