Numerical simulation of seasonal distribution of precipitation over the eastern Mediterranean with a RCM

Abstract

Regional climate model (RCM) RegCM3 with 50 km horizontal resolution driven from the lateral boundaries by the data from NCEP/NCAR re-analysis is used in a series of ten climate downscaling experiments over the eastern Mediterranean (EM) region. Results of the experiments are characterized by seasonal precipitation patterns with notable offshore precipitation zones posi- tioned *50 km westward of a less intense precipitation zone over the coastal area. Atmospheric processes deter- mining the distribution of seasonal precipitation patterns in the EM are analyzed based on results of the RCM experi- ments performed. Level of success of the model repre- sentation of the actual precipitation over the ECM appears to be depending on that of precipitation balance over dif- ferent parts of the domain. Excessive moisture convergence over a sub-area usually takes place at the expense of moisture divergence from neighboring areas. Synoptic mechanism causing formation of the precipitation zone in the offshore zone appears to be associated with the role of meridionally oriented atmospheric trough systems extend- ing from Scandinavia or Siberia to the EM during the period with rainy events. In such situations, air flows with strong northern components lead to intense transport of cold air masses to the EM. Meeting of the cold air masses the warm and humid air over the sea surface in the offshore zone causes formation of persistent squall lines and heavy rains there. Such processes may continue quite long as long as the troughs are stationary.