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The Sensitivity of Middle East Precipitation and Cloud Forecasts to Changes in Eastern Mediterranean Sea Surface Temperatures

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Final rept. 1 Oct 1986-31 Dec 1988

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Air sea interaction over the eastern Mediterranean plays an important role in shaping the weather of the Middle East. In this region, the year can be divided into two main seasons, a hot dry summer from April to September and a cool wet winter from October to March. Precipitation in this region is usually associated with migratory cyclones which cross the Mediterranean and bring cold air masses from Europe. Several recent statistical studies of this region have shown that there is a very high correlation between the sensible and latent heat fluxes from the eastern Mediterranean and the corresponding seasonal precipitation over this region. While these studies clearly demonstrate the importance of the sea, they do not explain the physical processes involved. To further understand this relationship, we have run a series of numerical experiments with a global model which based on the AFGL baseline model. A set of eleven 96 hour forecast were run. In each case two experiments were conducted, one in which the sea surface temperatures were fixed at their climatological monthly mean values and one in which the temperature of the eastern Mediterranean was increased by to 2.5 degrees. In the control runs, it was found that rainfall in this region was produced primarily by convective scheme of the model. In the anomaly runs, the rainfall increased mainly over the area of the imposed anomaly and over the surrounding region. The increase in rainfall was traced to the combined effects of additional moisture availability due to enhanced evaporation and increased convective activity due to the destabilizing effect of heating from below by the enhanced sensible heat flux.

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  • Meteorology

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