Decadal trends in the east Atlantic-west Russia pattern and Mediterranean precipitation

Investigation of the role of the east Atlantic-west Russia (EA-WR) teleconnection pattern in determining the variability of the monthly mean Mediterranean area precipitation is performed. Space correlations between the mean monthly precipitation and the EA-WR index during 1950-2000 have been calculated. The EA-WR/precipitation correlations are statistically significant over the eastern Atlantic and southeastern Mediterranean regions. Two pairs of 10-year periods characterized by low and high EA-WR regimes have been selected. The EA-WR/precipitation correlation patterns have been calculated for each of the periods. Common features that characterize the periods with the two EA-WR regimes are determined. One of the zones with the notable differences between the correlation patterns is found located over the eastern Mediterranean (EM) region. To determine the mechanisms responsible for the differences we analyse the low and high EA-WR low-troposphere circulations characterizing periods with EM precipitation (CEMP). The differences in the correlation patterns are explained by variations in the air mass transport to the EM area during the wet December-February (DJF) months during the two EA-WR regimes. Namely, during the low EA-WR years the CEMP is characterized by mean atmospheric flow transporting the air masses from the Atlantic to the EM. On the contrary, for high EA-WR DJF months the CEMP is typically characterized by advection to the EM of the air masses from central Europe. This finding allows explanation of the observed precipitation decline over the EM during the last several decades of the past century in terms of the positive trend of the EA-WR.