Decadal trends of main Eurasian oscillations and the Eastern Mediterranean precipitation

The role of the two main European low-frequency oscillations - the East Atlantic/West Russian (EA/WR) and the North Atlantic Oscillation (NAO), in controlling the precipitation in the Eastern Mediterranean region is investigated based on the NCEP/NCAR reanalysis and the Israeli precipitation data for 1958-1998. The data on the EA/WR and NAO indices, received from the NCEP Climate Prediction Center, are also adapted. Composite mean sea level and precipitation anomaly patterns are constructed and analyzed. In addition to the widely investigated positive NAO trend, another, also positive EA/WR trend characterized atmospheric developments during the period. During NAO positive months, the EA/WR-associated positive SLP anomaly areas were shifted from the east Atlantic to southwest Europe. The areas were shifted to the north during the NAO-negative months and were located over central and northern Europe. This demonstrates that the use of fixed pressure NAO patterns may be not the optimum way to understand climate variability. Analysis of the NAO, EA/WR patterns, as well as that of their decadal trends, demonstrated a relationship between the main European oscillations and the EM precipitation. The results allow explanation of the observed reduction of the north Israeli precipitation by the EA/WR positive trend during the period.