Can Saharan Dust Serve as Cloud Nuclei for Boundary-Layer Clouds in South Florida?

Aerosols have a large influence on global weather and climate patterns, making accurate measurement and model representation of their concentrations very important. Dust in particular is a unique aerosol, in that it is capable of nucleating warm liquid-only clouds and can serve as the nuclei for ice clouds. The Sahara is arguably the world's largest dust source region. In South Florida, Saharan dust events are of particular importance; dust outflows from the Sahara regularly travel across the Atlantic, reaching Florida primarily during the three month period from June to August. By the time the Saharan dust reaches Florida, the dust has descended to overlie the marine boundary layer. Satellite-derived aerosol optical depths are often used within aerosol-cloud interaction studies, but it is less clear if this is appropriate for dust layers because the dust layers can be elevated and may not be vertically collocated with the cloud layers. South Florida's CAROb (Cloud-Aerosol-Rain-Observatory) has been recording cloud condensation nuclei (CCN) counts on the surface, along with depolarization lidar measurements since 2011. These measurements have been used in part to observe and analyze dust events during the summers of 2012 and 2013. The purpose of this project is to assess if, when dust is present overhead, the presence of dust can also be detected within the boundary layer, as elevated CCN measurements at the surface. If so, this indicates that the dust can affect the boundary layer clouds. The project focuses on three time periods in particular when dust was observed above South Florida, and compares them to the more pristine time periods before and after the dust episodes. Back trajectories and space based lidar help assess the descent of the dust layers as they traveled across the Atlantic.