AGS-PRF: Direct Radiative Effects of Saharan Dust on the Dynamics of the African Easterly Jet and African Easterly Waves

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The large-scale atmospheric circulation over North Africa during summer is characterized by three striking features: the African easterly jet (AEJ); African easterly waves (AEWs); and large plumes of Saharan mineral dust aerosols. The central objective of this research is to determine the effects of Saharan dust on the linear dynamics and nonlinear evolution of the AEJ-AEW system. To achieve this objective, several tasks that will be carried out to answer the following questions: Can dust-radiative heating destabilize an otherwise stable AEJ (or vice versa)? If so, what aspects of the dust - concentration, spatial gradients, emission variability, etc. - affect the linear stability of the AEJ? How does the dust physics manifest in terms of the spatial structure and energetics of the AEJ? Are there particular locations and combinations of dust concentration and distribution that will optimize the linear growth (or decay) of AEWs? As the AEWs grow to finite amplitude, how does the dust affect their structure? Are there particular locations and combinations of dust concentration and distribution that will optimize the development of AEWs? And how does the AEJ-AEW system respond to a time varying dust plume, one that varies either periodically or episodically?To answer these questions, and others, the Weather Research and Forecasting (WRF) model, which is coupled to a dust tracer model, will be used to run a systematic sequence of experiments with and without dust. The data from the simulations will be analyzed and compared using standard methods. The analyses will provide information on the effects of dust on the following: growth rate, propagation, and structure of AEWs; formation of critical layers, which have been shown to play a role in tropical cyclogenesis; and local and global energetics of the AEJ-AEW system.Intellectual Merit:The intellectual merit of the research includes: advancing understanding of how Saharan dust-radiative feedbacks, which depend on a combination of the dust concentration and its spatial distribution, affect the linear growth and nonlinear development of AEWs; developing insights into the relationship between the spatial-temporal variability of Saharan mineral dust and the spatial-temporal evolution of the AEJ and AEWs; and improving forecasts of the dust-modified AEJ-AEW system and its possible effects on tropical cyclogenesis over the Atlantic Ocean.Broader Impacts:The broader impacts of this work includes: advancing knowledge on the sensitivity of AEJ-AEW system to the dust plume properties (e.g., location, concentration, spatial gradients), which could aid in the prediction of AEWs and thus tropical cyclones; demonstrating the importance of dust radiative heating on AEWs, which could motivate future studies to examine dust radiative effects on other synoptic scale disturbances that are associated with the dust source regions around the world.