On sources of dry tropical air in the environment of Atlantic tropical cyclones

Recent studies on the negative impacts of the Saharan Air Layer on Atlantic tropical cyclones have frequently made the same assumption: that dry tropical air in the immediate environment of the storms was of Saharan origin. Dunion and Marron (2008) made this assumption in averaging a set of soundings to produce mean SAL and non-SAL soundings. But these studies have typically neglected the role that large-scale subsidence plays in producing dry tropical air masses. In this study, we use NCEP GFS analyses to compute a climatology of 6-day backward trajectories over the Atlantic and Africa over the period June-August 2006. The trajectories are used to determine origin locations of dry air masses and vertical displacements of air parcels that may contribute to drying. The climatology of trajectories will then be used to determine the relative contributions of the SAL and subsidence to very dry air masses in the tropics during the June-August portion of the hurricane season when the SAL is most active.