Summertime variability of Mediterranean evaporation: competing impacts from the mid latitudes teleconnections and the South Asian monsoon

Abstract

AbstractInterannual variability of Mediterranean evaporation and its links to regional climate during summer are investigated based on evaporation data from the Woods Hole Oceanographic Institution dataset. An EOF (Empirical Orthogonal Function) analysis performed on the monthly means (i.e., separately for June, July, August, and September time series) revealed two leading modes of evaporation variability, characterized by the monopole (EOF-1) and zonal dipole (EOF-2) patterns. These modes explain altogether more than 60% of the total variability of Mediterranean evaporation for each month. In all summer months, the EOF-1 reflects an interdecadal change signal characterized by below normal evaporation in 1970–2000 and above normal evaporation before and after this period. This mode is associated with the Atlantic Multidecadal Oscillation. The EOF-2 pattern reflects interannual variations of Mediterranean evaporation that differ significantly from month to month. The reason for this difference is the changing roles of regional teleconnections, such as the summer North Atlantic Oscillation (SNAO), the Scandinavian and East Atlantic teleconnections, and the Asian monsoon. The impacts of these teleconnections on Mediterranean evaporation are highly variable both in space and time. The largest impact of the SNAO on Mediterranean evaporation is detected in early summer, but its impact weakens and disappears towards the end of the summer season. An opposite tendency is obtained with the Asian monsoon, having the strongest impact on evaporation in late summer. The study suggests that these teleconnections impact Mediterranean evaporation mostly through atmospheric dynamics (the SNAO) and thermodynamics (the Asian monsoon) in early and late summer respectively.