Application of Non-Divergent Barotropic Model And The Single Level Primitive Equation Model To Predict Flow-Patterns In Sudan

Abstract

Two simple numerical weather prediction models have been applied to identify and forecast the flow patterns over Sudan region. These are the non-divergent barotropic model and the single level primitive equation model, which use the conservation of absolute and potential vorticity as the guiding principle respectively. Using, the 700-hPa level horizontal objectively analyzed wind component fields, period 12Z 3 August 1988 to7 August 1988,to describe the flows at the level of non-divergence. A regular closed grid point structure (2.5o× 2.5o) was used to define the horizontal domain, which extends from 20oS to 35oN latitude and 10oW to 45oE longitude. Factors, such as analysis of the initial map, domain size, grid size, handling of north-south and eastwest boundaries, and the finite difference techniques, have been examined carefully. MATLAB software program codes have been constructed to prepare the initial and forecast fields for the barotropic forecast model (stream function field) and the single level primitive equation model (geopotential height field). The heavy rainfall, which occurred in Sudan on 4th and 5th August 1988, has been taken as a case study. The main meteorological factors involved in the heavy rainfall are; the presence of a trough aligned northeast to southwest, associated with the deep cyclonic circulations centered nearly over Khartoum. Three experiments have been carried out with different time interval forecast (24,12,and 6 hours) to investigate the predictive capabilities of the models .The 6 hours forecast produced by the two models appeared to be better (in comparison to the actual map).The success increases as the time interval decreases.