Declining summer circulation over the Eastern Mediterranean and Middle East

Abstract

This study investigates the climatological and interdecadal (1980–2024) variations in summer (June–August) circulation over the Eastern Mediterranean and Middle East (EMME) using ERA5 global atmospheric reanalysis. The EMME summer climate is governed by the evolution of several key atmospheric circulation features: (1) High mean sea level pressure over the eastern Mediterranean (EM), along with a thermal low over the Arabian Peninsula (AP) and, (2) strong subsidence and downward advection of temperature in mid-troposphere centered over the EM, stretching into northern parts of Africa and AP. Diabatic heating released from ISM rainfall induces equatorially trapped westward-propagating Gill-type Rossby wave structure to its west. The interaction of this structure with the midlatitude westerlies gives rise to the aforementioned circulation features over the EMME. Our analysis reveals a substantial decline in the intensity of these circulation features over the study period, indicating an overall weakening of the summer circulation over the EMME. Further investigation points to a marked reduction in the subtropical westerly jet and the underlying westerlies during summer. This weakening may have contributed to reduced subsidence and a further decline in summer circulation strength over the EMME. Consequently, both Etesian winds over the EM and Shamal winds over the northern AP have shown notable declines in their occurrences. The weakened summer wind system has contributed to an abnormal increase in human-perceived temperatures and reduced dust activity.