The Inclusion of Aerosols Impacts on the Forecasting of African Easterly Waves that Develop Hurricanes

Previous studies have shown that the inclusion of aerosols in general circulation models (GCMs) can significantly reduce errors in weather forecasting over aerosol-rich areas, as well as increase our understanding of the aerosol impacts on specific weather systems. For this study, we incorporate aerosols into the Global Forecasting system (GFS v14) to investigate their effects on African easterly waves (AEWs) that eventually spawn hurricanes over the Atlantic Ocean. In particular, we focus on hurricanes Gert and Harvey, both which originated from AEWs during August, 2017.

Two sets of experiments are conducted. The first experiment is an aerosol blind run, where data assimilation does not consider aerosol radiative effects (CTL). The second experiment is an aerosol aware run, where data assimilation accounts for the influence of aerosols on the radiance observation operator (AER). When comparing the analysis fields from these two experiments during August, 2017, we find that for AER, the atmosphere over North Africa is characterized by having a stronger African easterly jet (AEJ), as well as a warmer and drier Saharan atmospheric boundary layer (15-30°N, 1000-500 hPa). The observed impacts on the initialized fields are driven by Saharan mineral dust, which is particularly active during this time period. In this study, we explore the implications of these aerosol-induced changes to the atmosphere on the AEWs that spawned Gert and Harvey, as well as how it affects model forecasts during their pre-genesis stage.