Dynamics of gap winds in the Great Rift Valley, Ethiopia: emphasis on strong winds at Lake Abaya

Abstract. Lake Abaya, located in the Great Rift Valley (GRV) Ethiopia, is affected by regularly occurring strong winds that cause water waves, which turn affect lake's ecology and food web. The driving forces for these winds, however, are yet unexplained. Hence, main goal of this study to provide a physical explanation formation GRV especially at Abaya. To aim, two case studies were performed based on measurements, ERA5 reanalysis data mesoscale numerical simulations conducted with Weather Research Forecasting (WRF) model. revealed both cases gap flow downstream narrowest highest part (i.e. pass) led high wind speeds up 25 m s−1. Two types identified: north-eastern south-western flow. directions line orientation valley axis depend air mass distribution north south resulting along-valley pressure gradient. was determined position Intertropical Convergence Zone relative GRV. colder upstream studies. During day, convective boundary layer warmer side heated more strongly quickly than mass. most suitable variable describing timing found be gradient pass height, corresponds roughly 800 hPa level. In exhibited daily cycle, illustrates importance thermal forcing due differential heating over complex terrain addition large-scale differences. start, strength, duration within depended location. For cases, strongest occurred after sunset ongoing night corresponding lee slope. captures events qualitatively well but weaker simulations. future climatological analysis flows.