Impact of Interactive Aerosol on the African Easterly Jet in the NASA GEOS-5 Global Forecasting System

Abstract

he real-time treatment of interactive, realistically varying aerosols in a global operational forecasting system, as opposed to prescribed (fixed or climatologically varying) aerosols, is a very difficult challenge that has only recently begun to be addressed. Experiment results from a recent version of the NASA?s Goddard Earth Observing System (GEOS-5) forecasting system, inclusive of interactive-aerosol direct effects, are presented in this work. Five sets of 30 five-day forecasts are initialized from a high quality set of analyses previously produced and documented, to cover the period from 15 August to 16 September 2006, which corresponds to the NASA African Monsoon Multidisciplinary Analysis (NAMMA) observing campaign. Four forecast sets are at two different horizontal resolutions, with and without interactive-aerosol treatment. A fifth forecast set is performed with climatologically varying aerosols. The net impact of the interactive aerosol, associated with a strong Saharan dust outbreak, is a temperature increase at the dust level, and a decrease in the near-surface levels, in agreement with previous observational and modeling studies. Moreover, forecasts in which interactive aerosols are included depict an African easterly jet (AEJ) at slightly higher elevation, and slightly displaced northward, with respect to the forecasts in which aerosols are not included. The shift in the AEJ position goes in the direction of the observations and agrees with previous results.