Kyu-Myong Kim

GESTAR/Morgan State University and NASA/GSFC, 613.2

Title: The role of African easterly wave on dust transport and the interaction between Saharan dust layer and Atlantic ITCZ during boreal summer

Every year during the boreal summer, Saharan dust outbreaks transport large amounts of dust from the North Africa continent to the North Atlantic ocean.  Saharan dust layers are known to have strong impacts on weather and climate, and water cycle over the North Atlantic, through their interaction with tropical convection.  However, in-depth understanding of the physical mechanisms and dynamics of interaction of Saharan dust with tropical convection and associated atmospheric phenomena is still very much lacking.

This talk is focused on an observational and modeling study of the mechanism of Saharan dust transport and interaction of radiative forcing, tropical convection and large-scale dynamics associated with Saharan dust outbreaks over the North Atlantic.  I will present results showing the relationship between dust outbreaks and the African easterly waves, and its interaction with the Atlantic Inter-Tropical Convergence Zone (ITCZ) based on the case of July 2007 when four consecutive dust outbreaks were observed for about a three-week period, using Terra/Aqua, and Calipso observations as well as MERRA data. Composite patterns of dust outbreaks are also constructed based on the 11-year MODIS aerosol. Results show that increased dust outbreaks are associated with modulation of the African easterly jet and enhanced amplitudes of westward propagating easterly waves.  Dust radiative forcing may further increase north-south temperature gradient, leading to increased  dynamical instability to the south of the dust layer, and thereby increase rainfall on the northern part of ITCZ.  We also find two principle tracks of dust transport by easterlies wave 15-25N and 5-10N respectively.  I will discuss the dynamics of dust propagation and interactions of rainfall in the Atlantic ITCZ along these two tracks, based on two GEOS-5 model integrations, with and without the aerosol radiative forcing, and compared with the observed patterns of dust outbreaks.

Branch Seminar Series Coordinators