The evolution, structure and effects of orogenic mesoscale convective systems in Ethiopia during Kiremt

In this study, MCS activity within the Blue Nile and Atbara catchment areas was documented for the entire 1995 Kiremt season. The results revealed the existence of a third genesis zone for MCS development in Africa. The Fifth-Generation PSU/NCAR Mesoscale Model (MM5) - Version 2 was used to simulate the dynamics associated with MCS formation. The purpose was to test the hypothesis that the observed formation of mesoscale convective systems in this region was largely self-exciting from local wind-systems. The results of the numerical simulations revealed that thermally driven orographic flow systems interact with ambient flow systems to create a favorable environment for cumulus formation and organize on the mesoscale. The fact that the development scenario closely paralleled the observed growth scenario in the absence of synoptic-scale forcing not only supports a hypothesis of orogenic development, but also isolates a relatively simple mechanism of development consistent with known dynamical principles. Based on a set of seven numerical case studies, it was possible to develop a conceptual model of the orogenic development processes observed in the simulations.