A Modeling Study of Tropical Intraseasonal and Synoptic Variability in West Africa and the Americas

Colorado State University, Fort Collins CO

Investigators

Abstract

This project is a study of tropical easterly waves with two distinct components. The first component is an examination of the influence of the Madden-Julian Oscillation (MJO) on African Easterly Waves (AEWs). The research would focus on the hypothesis, motivated by the PI's prior research, that the MJO affects the "triggering" of AEWs in the region of the Darfur highlands at the entrance to the African Easterly Jet (AEJ). The proposed mechanism for this influence is the westward propagation of MJO-induced Rossby waves from the Indian Ocean, which modulate the meridional transport of moisture in the AEJ entrance region. The second component addresses the origins of easterly wave activity in the Caribbean Sea and the Eastern Pacific (EP). Previous studies have argued that easterly waves in this region are actually AEWs which become re-invigorated after crossing the Atlantic. Work performed here will test the alternate hypothesis that the conducive basic state and multiple vorticity sources in the region should suffice to generate easterly waves in the absence of any "seeding" from trans-Atlantic AEWs. The work performed in both components consists of numerical experiments with the Weather Research and Forecasting (WRF) model, a regional model in which the boundary conditions can be filtered to allow or exclude the influence of Rossby waves and AEWs propagating into the model domain. Tropical easterly waves are the precursors of tropical cyclones (including landfalling hurricanes), and thus are important for the prediction of significant weather hazards. Thus, the work has societal broader impacts through its relevance for practical weather prediction. In addition, the work will support and train two graduate students, thereby providing for the development of the future workforce in this research area.