The simulation of the occurance of a sand storm using the Egyptian numerical model

Among different weather phenomena that occur in subtropical Africa, one stands out as being most unpleasent for the population of this area, most hazardous for transport and navigation are duststorms. These storms are frequently invading the area by more than 20-25 storms / year. As these storms are small-scale phenomena, there is some difficulty in its analysis and forecasting. Usually these storms bring up more than 1350 μg/m3 of sand load near the earth surface.
In present work, a dust model was under developing at Cairo numerical weather prediction NWP center to forecast and monitoring the dust and sandstorm. An equation for sand concentration was added to the hydrostatic primitive Egypt-eta model (Yousef 98). The model depends on the soluation of a set of primitive equations using the generalized vertical coordinate, which follow the orographic structure. A forward — backward time integration scheme, as economic scheme, was used with the part control the fast waves to increase the time step. Forward —centered time integration scheme was used with the advection terms. A semi- Lagrangian advection scheme with fourth order accuracy has been modified to conserve the mass of dust. It uses full physical parameterization package as a detail representation of radiation components, surface physics-soil hydrology processes and comprehensive scheme for the planetary boundary layer has been used. In addition, eight levels in the boundary layer have been used to improve the forecasting of the surface temperature and capture well process occurring in the planetary boundary layer. The dust module includes dust emission as a function of (vegetation cover- soil type and texture — soil wetness — friction velocity), dust deposition (wet and dry), horizontal and vertical advection and vertical diffusion through an improved formulation of planetary boundary layer.
Two cases with very remarkable sandstorms were described and investigated through this study. The model outputs for 72 hours were validated and verified with satellite images and visibility as actual data in addition, the aerodynamical parameters (friction velocity, wind speed, vertical motion) for the sake of comparison which are the main factors in the dust emission.