干旱区生态环境知识资源中心

A phenomenon characterized by a tongue of low pressure extending northward from the southern Red Sea [Red Sea Trough (RST)] toward the eastern Mediterranean Sea (EM) is analyzed. In general, the RST is associated with hot and dry weather, resulting from east-southeasterly flows in the lower troposphere. In some cases, the RST is found to be accompanied by an upper-tropospheric trough extending from the north over the EM. Such conditions are associated with unstable stratification, favoring the development of mesoscale convective systems. This kind of RST has been defined as an "active’’ RST (ARST). The ARST phenomenon represents a serious threat to human society in the northeastern Africa-southeastern Mediterranean region, being in some cases associated with devastating floods. In this study, a conceptual model of the ARST phenomenon is discussed, and then an algorithm for the identification of ARST events is presented. The identification algorithm has been applied to a multiyear NCEP-NCAR reanalysis data archive for both RST and ARST events. From the results of a composite analysis of several different atmospheric flow parameters associated with ARST events, the key features associated with ARST events are identified. The results from the analysis of the composite patterns support the suggestion that high amounts of moisture transported from tropical Africa in the form of an atmospheric river to the Red Sea-EM play a key role in determining the intensity of the ARST events.