Tadesse, Tsegaye (National Meteorological Services Agency, Addis Ababa, Ethiopia)
Frontal systems (including Storms and Depressions) over Mediterranean Sea usually propagate estwards and sometimes cross the Arabian peninsula influencing the weather of Ethiopia during the dry "BEGA" season (i.e October to January). This season is the period of harvesting in which rainfall activity influences the production of agriculture which is the basic economy of the country. The role of these systems in altering the local climate is not well documented and still not understood in detail. The frequency, structure, movement, and influence of these frontal systems which produce many changes in the atmospheric circulation and weather of Ethiopia is still largely unknown. In this study attempt has been done to investigate the influence and contribution of Mediterranean frontal systems based on routine surface observations of synoptic stations, surface synoptic charts, upper air synoptic charts, and satellite imageries of METEOSAT and NOAA which were captured every half-hour using PDUS facilities.
The study indicated:
- the most preferable trucks of the frontal systems to inhance the rainfall of Ethiopia during the season by interacting with the tropical airmass;
- The indirect effects of the frontal systems by displacing the high over Arabian peninsula (or the Siberian ridge extension) to the Arabian sea surface,
- the inhanced weather activity over Ethiopia when the Arabian sea storms or depressions are propagating westwards to Ethiopa and interact with the east Mediterranean frontal systems land-falling over the Arabian peninsula along the great Rift-Valley, and
- the influence of the upper air trough in the westerlies at the middle troposphere and the Subtropical Jet (STJ) which is associated with the eastward propagating Mediterranean frontal systems over Ethiopia and adjoining regions.
By its brief emphasis, this paper may contribute to improve the weather forecasting and issuing an early warning capabilities of Short & Medium Range Weather Forecasting Section and to the further research activities on the estward propagating Mediterranean frontal systems as well as the westward propagating Arabian Sea storms or depressions and their coupled effects on the Ethiopian weather.