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ItemPerformance of WRF-ems Rainfall Output over Khartoum Area for August 2013(University of Khartoum, )The performance of the numerical model Weather Research and Forecast - environmental modeling system (WRF-ems) rainfall output over Khartoum area for the year 2013 is studied. Two nested domains were created to refine the model resolution. Using two sampling methods for forecasted Data, Nearest Neighborhood (NN) and Weighted Average (WA).For each sampling methods, WRF-ems rainfall output for the four-days lead forecast, three-days lead forecast, two-days lead forecast and one-day lead forecast was taken versus Khartoum rain gauges actual data, and thresholds of 0.01, 5, 10 and 20mm. Contingency table created and four statistical performance indicators were calculated from it. Namely Accuracy, False Alarm Ratio (FAR), Equitable Threat Score (ETS) and Heidke Skill Score (HSS). NN sampling method gave best scores than WA sampling method. Two day lead and one day lead, they were reflected the accurate forecast especially for light to medium rainfall with Accuracy ranging from 80% to 89 %, FAR ranging from 0.6 to 0.7, and 0.5 for ETS, while HSS had a poor performance and its value ranged in 0.09 – 3.6 which are considered small values. Results of verification show that the model accuracy increases as thresholds increases and increases also as forecast days lead decreased
ItemApplication of Non-Divergent Barotropic Model And The Single Level Primitive Equation Model To Predict Flow-Patterns In Sudan(University of Khartoum, 2015-05-14)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.