Using high-resolution numerical simulations to understand the role of East African mountains in the initiation of long-lived episodes of organized convection

The prediction of convectively-generated precipitation remains a challenge especially where observation networks are unable to resolve mesoscale circulations. Observational studies (e.g., Carbone et al. 2002, Laing et al. 2007) have documented the common occurrence of deep convection and heavy rainfall as episodes that exhibit temporal and spatial coherence across continents during the warm season. These episodes are comprised of mesoscale convective systems (MCSs), which account for most of the seasonal precipitation in the Sahel (Mathon et al. 2002). Previous studies over the US have examined the role of planetary boundary layer circulations in the initiation of convection near high terrain (Trier et al. 2006). The current work examines the initiation and evolution of episodes at or within several hundred km west of the Ethiopian Highlands and the Darfur Mountains. These orographically-driven systems propagate westward, aid in easterly wave generation, and modulate the diurnal cycle of rainfall in the African Monsoon Multidisciplinary Analysis (AMMA) core region.

The Advanced Research Weather Research and Forecasting (WRF) modeling system is used to simulate a convectively-active 7–10 day period during the AMMA Special Observation Period (SOP3). The model is integrated over a large sub-continental domain that encompasses the mountains and the central Sahel and uses a deep convection-permitting horizontal grid spacing of 3 km. A preliminary simulation employs a time-averaged lateral boundary condition that varies only with time of day. Results will be presented at the conference.