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Climatology and Dynamics of the Summer Etesian Winds over the Eastern Mediterranean

October 2, 2013

The Etesians are persistent northerly winds that prevail over the eastern Mediterranean during summer. We have developed a climatology of Etesian outbreaks over the Aegean and investigated their vertical organization based on the ERA40 dataset. Their variability arises from high frequency variability originating in the midlatitudes, interannual and intraseasonal variability controlled by the South Asian monsoon and a local diurnal cycle. Consistent with the monsoon influence, Etesian outbreaks are most frequent from mid July until mid August. In agreement with previous studies, a negative trend in the incidence of Etesian outbreaks is detected during the overall June-September period, which is strikingly strong for September but diminishes in June. The strengthening of the Etesians by day over the central and southern Aegean results from the deepening of the Anatolian thermal low due to the daytime sensible heating near the surface. The timing of an outbreak onset is controlled by wave disturbances originating over the North Atlantic that trigger the development of a strong ridge over the Balkans, which induces anomalously strong northerly flow and subsidence over the Aegean. During Etesian outbreaks sharp tropopause folds and stratospheric intrusions of high potential vorticity descend deeply into the troposphere.

Tyrlis E, Lelieveld J, in press. Climatology and Dynamics of the Summer Etesian Winds over the Eastern Mediterranean, Journal of the Atmospheric Sciences, 2013, doi: http://dx.doi.org/10.1175/JAS-D-13-035.1. Article (subscription required).

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