Long-Term Variations in Summer Circulation Over the Eastern Mediterranean and Middle East

This study examines the climatological and long-term (1980–2019) variations in summer circulation patterns (June–August) over the Eastern Mediterranean and Middle East (EMME) region, utilizing ERA5 global atmospheric reanalysis data. The summer climate of the EMME is influenced by the development of several prominent atmospheric circulation features: (1) a pronounced east-west pressure gradient, resulting from elevated mean sea level pressure over the eastern Mediterranean (EM) and a thermal low over the Arabian Peninsula (AP); (2) significant subsidence spanning the EM, northern Africa, and the AP; and (3) the presence of a warm core over the EM, linked to downward temperature advection. These atmospheric features are closely linked to the Indian Summer Monsoon (ISM) system. Diabatic heating from ISM rainfall initiates westward-propagating equatorially trapped Rossby waves of the Gill-type, which interact with westerlies to influence the summer circulation over the EMME.

Analysis indicates a notable decline in the intensity of these atmospheric patterns over the study period, signaling an overall reduction in the strength of the summer circulation. Despite this, ISM activity has intensified in recent decades, underscoring a growing mismatch between the remote driver (ISM) and the EMME as a responsive region. Further examination reveals a significant weakening of the subtropical westerly jet and associated westerlies during summer, which appears to have reduced subsidence over the region and contributed to the observed decline in circulation strength. As a result, both Etesian winds over the EM and Shamal winds over the northern AP have experienced marked reductions in frequency. The diminished summer wind systems have led to an unusual rise in human-perceived temperatures and a reduction in dust activity.