Extended Abstract (184K)P2.20
Initiation of Mesoscale Convective Complexes over Ethiopian Highlands: A Precursor to Tropical Cyclogenesis
Christopher M. Hill, North Carolina State University, Raleigh, NC; and Y. L. Lin
A tropical disturbance, which would later become Hurricane Alberto (2000), was traced back in time as a mesoscale convective complex (MCC) to the Ethiopian Highlands, where the MCC first developed. Satellite imagery indicates that the MCC developed in the morning of 29 July 2000 from a mesovortex, which formed over the lee of the Ethiopian Highlands in the afternoon of 28 July 2000. A 200-mb easterly jet was found immediately upstream of the Ethiopian Highlands at 0000 UTC 26 July 2000, prior to MCC development, using analysis data from the Navy Operational Globally-Analyzed Prediction System (NOGAPS). A monsoon trough was found, at 600 mb, over the Gulf of Aden, with the base of the trough positioned over Djibouti. The Mesoscale Atmospheric Simulation System (MASS), with boundary conditions from NOGAPS analyses, was used to simulate the environment near the time of observed MCC development starting at 0000 UTC 28 July 2000. Model results showed two areas of maximum vorticity developing on the lee side of the Ethiopian Highlands at 1800 UTC 28 July 2000. At 0600 UTC 29 July 2000, the maximum vorticity area located to the west of the Ethiopian Highlands intensified and tracked westward into eastern Sudan. The resultant vortex was present at the end of the simulation (48th hour). We hypothesize that the MCC is formed by the phasing of the low-level orographically-induced mesovortex located to the west of the Ethiopian Highlands, the very moist (conditionally unstable) conveyor belt associated with the monsoon trough from Indian Ocean, and the upper-level divergence associated with the easterly jet streak.
Poster Session 2, Orographic Precipitation/Operational and Numerical Weather Prediction (with Coffee Break)
Wednesday, 19 June 2002, 9:15 AM-11:00 AM
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