The Summer Circulation in the Eastern Mediterranean and the Middle East: Influence of the South Asian Monsoon and Mid-Latitude Dynamics

Abstract

The summer circulation in the Eastern Mediterranean and the Middle East (EMME) is dominated by persistent northerly winds (Etesians) whose ventilating effect counteracts the adiabatic warming induced by subsidence prevailing over the eastern Mediterranean. The ERA40 dataset is used to investigate the South Asian Monsoon and mid-latitude influences on the EMME circulation. Consistent with past modeling studies, in late spring an upper level warm structure and subsidence area expanding towards the EMME are identified, attributed to Rossby waves excited by monsoon convection. Steep sloping isentropes develop over the EMME with subsidence mainly over the eastern Mediterranean and Iran, where orographically induced circulation patterns enhance the mid-latitude northwesterly flow and the air mass subsidence along isentropes. These phenomena have a maximum in July and are strikingly synchronous to the convection over northern India where the background state favors a stronger Rossby wave response. The monsoon induced large-scale background state over the EMME is modified by synoptic activity originating in the Atlantic that introduces high frequency variability over the EMME. During ‘etesian outbreaks’ a ridge develops over the Balkans and sharp tropopause folds appear over the Aegean.