Monday, 15 January 2007: 1:45 PM
The Instability associated with the Cross-Atlantic Transport of Saharan Dust and its Meteorological Implications
212A (Henry B. Gonzalez Convention Center)
During late spring and early fall, Saharan dust is transported toward the Tropical North Atlantic Ocean by African easterly waves. The warm and dry anomalies associated with the Saharan dust, the Saharan Air Layer, have a two-fold impact on the atmospheric instability over the Tropical North Atlantic Ocean. First, the anomalies are located at the top of the boundary layer, enhancing the inversion strength and reducing the conditional instability. The enhanced inversion strength suppresses the occurrence of deep convection and the development of tropical cyclones. Second, the temperature gradient associated with the warm anomalies enhances the mid-level jet that increases the barotropic and baroclinic instability. In this study, we analyze a 27-year model run (GEOS-4) of dust transport over the Tropical North Atlantic Ocean using GMAO assimilated winds and temperatures for 1979-2005. We will evaluate that the episodes of transport of Saharan dust into the North Atlantic Ocean can be described by an index representing the activity of African easterly waves near the coast of West Africa. We will correlate the parameters of instability with this index to examine the relationships between the transport of Saharan dust and the instability over the Tropical North Atlantic Ocean. The parameters of instability include convective available potential energy (CAPE) and convection barrier for conditional instability, and gradients of potential vorticity for barotropic and baroclinic instability. Implications on tropical cyclone developments and genesis will also be discussed.