Precipitation processes in the Middle East.

A regional climate model, RegCM2, is used to investigate the relative importance of storm tracks and topography in generating precipitation in the Middle East. The model is run for five years (1990 thru 1994) at 25km horizontal resolution forced at the boundaries by the ECMWF-TOGA analysis. Six sub- regions that exhibit precipitation regimes disparate from one-another are identified and examined. The models ability to reproduce these precipitation regimes was tested with mixed results. RegCM2 is better able to capture the scale of the interannual variability than the ECMWF analysis. In order to assess the hypothesis that precipitation is controlled by both storm-track location and the presence of topography, we performed multi-variate regressions between monthly precipitation and relevant indices. Results indicate that the storm track indices are best correlated with the seasonal cycle of precipitation. The topographic indicator is better correlated with precipitation anomalies suggesting that the number and intensity of storms is less important in explaining interannual variations than whether they produce upslope flow, i.e. the storm location.

Figure 3: Standard deviation and mean of the seasonal precipitation associated with interannual variations for 1990 thru 1994.