Meteorological Conditions Leading To The Saharan Dust Events Observed Over South Florida In July 2012

The effects of Saharan dust on human health and the ecosystem have been thoroughly documented. However, the effects of that dust on local weather in general, and precipitation in particular, are not completely clear and are active areas of research. This study focuses on six Saharan dust events that reached Miami, FL, in July 2012. Using backward trajectories, the times when, and locations where, the dust lifted from the surface were identified, as were the meteorological conditions at the surface, 850mb, and 600mb levels. This permitted an examination of the relationships between the time the dust spent aloft, the source location and the concentration of the dust, measured in Aerosol Optical Depth (AOD), as it passed over South Florida.

The meteorological conditions that occurred during July 2012 from West Africa to South Florida were compared to climatological averages to determine any relationship with the large frequency of dust events. The daily averaged conditions were analyzed to identify the transport mechanism for the dust to reach South Florida. The position of the subtropical ridge during periods of active dust transport, and a prolonged period of inactivity, were noted. Neither the time the dust spent aloft, nor the location where the dust originated, was indicative of the concentration when it reached Miami. Dust lifting occurred in two major locations: the Libya/Algeria border, and another in Niger, with event 2 outlying in western Mauritania . The Nigerien events were all similar in strength (0.325 to 0.375 AOD), but the far North African origins ranged from the strongest to weakest events. The 850mb flow best represented dust transport. The orientation of the subtropical ridge was found to be crucial for transporting dust to South Florida, with southerly and westerly maxima and an east to west elongation of the ridge most conducive for transport. The fastest movements of dust across the Atlantic came during a westward expansion of the subtropical ridge. Forecasters at the NWS Miami forecast office can use the results of this study to increase their situational awareness concerning Saharan dust events. This is expected to increase the accuracy of dust forecasting over South Florida.