Relationship between the Indian summer monsoon and the large-scale circulation variability over the Mediterranean

• The anomalous characteristics of large-scale synoptic fields during extreme ISM years are analyzed.
• During strong ISM years a well organized Rossby wave pattern appears across Eurasia.
• Strong ISM years favor a poleward shift of the subtropical jet over Eurasia.
• In the strong ISM years Etesians and subsidence over eastern Mediterranean appear enhanced.
• The ISM influences the temperature regime over eastern Mediterranean as well.

In this study the impact of the Indian summer monsoon on the large scale variability of the atmospheric circulation over the Mediterranean is investigated on an inter-annual time scale. Composite and correlation analysis results are presented, outlining different circulation patterns in the upper and lower troposphere for strong and weak monsoon years respectively. For this purpose ERA-40 Reanalysis monthly mean data at various isobaric levels together with the standardized All India Rainfall Index for boreal summer (June–July–August–September) of a 44-year period were employed. During strong monsoon years many atmospheric circulation systems appear strengthened over Eurasia, resembling a well-organized Rossby wave train over the area. In the upper troposphere a meridional shift of the jet streams over the examined area was also identified during extreme monsoon years. On the other hand, in the lower troposphere enhanced northerlies (Etesians) appear to dominate over Eastern Mediterranean along with intensified subsidence during strong monsoon years.