Extended Abstract (120K)1C.6
A mesoscale modeling study of the formation of an African disturbance preceding tropical cyclogenesis
Christopher M. Hill, North Carolina State University, Raleigh, NC; and Y. L. Lin
As previously noted from Hill and Lin (2003), the tropical disturbance that would become Hurricane Alberto (2000) originated over the Ethiopian Highlands (EH) 5 days prior to cyclogenesis over the eastern Atlantic Ocean. Because this disturbance was remarkably coherent as it traversed the Sahel of Africa and emerged over the ocean, as shown with METEOSAT-7 satellite data, our interest lies in the formation of this disturbance in the vicinity of the EH. This study focuses on the mesoscale precursors to the development of this disturbance. The non-hydrostatic COAMPSTM model is used to simulate the development of the pre-“Alberto” disturbance as well as to conduct sensitivity tests that highlight key features in the mesoscale environment that contribute to the development of the initial mesoscale convective complex (MCC) and the associated mesovortex (MV) of this disturbance. Specifically, the effects of terrain, sensible heating, and latent heating on the convective and kinematic development of this disturbance are examined.
The no-terrain (NT) experiment indicates that a cyclonic shear zone along the left streamwise periphery of the African Easterly Jet (AEJ) is important to the development of cyclonic vorticity immediately west of the EH. The heat source of the EH surface and the surrounding moisture sources of the Red Sea, Indian Ocean, and the Congolese rain forests are shown to be crucial to the initiation of scattered afternoon convection, and the eventual maturity of the convection into an MCC, with the no-sensible-heat-flux (NSH) and no-latent-heat-flux (NLH) experiments. Additional sensitivity experiments excluding the effects of the planetary boundary layer (NPBL) and the presence of the Turkana Channel (NTCH) will be performed to investigate more precisely the formation mechanisms for the pre-“Alberto” disturbance.
Session 1C, Tropical Cyclogenesis I
Monday, 3 May 2004, 8:30 AM-9:45 AM, Napoleon II Room
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