New Observations of Miami Saharan Dust Events

Huge outflows of Saharan dust are regularly escorted westward by strong midlevel easterly winds. The dust provide a large-scale direct aerosol radiative forcing on climate and alter the atmospheric radiative heating profile. Filter sampling at the surface in Miami has provided a continuous time series since 1974, revealing an annual-mean aerosol loading that is dominated by dust, peaking in July. The filter sampling has recently been augmented with measurements of the aerosol vertical structure using a depolarization micro pulse lidar, of boundary layer cloud condensation nucleation activity, and broadband and spectral radiation measurements. Here we survey these new measurements for the summers of 2013 and 2014. One finding to date is that dustier days possess average CCN concentrations that are lower than on more pristine days, as well as a shallower CCN activation slope as a function of supersaturation. The finding is consistent with back trajectories that show eastern seaboard origins for the more visibly pristine days. This has public health implications for southern Florida.