10 Apr 2024
 | 10 Apr 2024
Status: this preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).

The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity

Dor Sandler, Hadas Saaroni, Baruch Ziv, Talia Tamarin-Brodsky, and Nili Harnik

Abstract. A unique chain connects the flow over the North Atlantic and the development of cyclones within the Mediterranean basin. One typical mechanism includes several successive processes: upper-level flow perturbations upstream cause Rossby wave breaking (RWB) events along the jet stream, which in turn develop into potential vorticity streamers. These streamers reach the Mediterranean, and through increased baroclinicity they enhance cyclonic activity in the region. Using ERA5 reanalysis data and rain gauge measurements, we provide a systematic analysis connecting wintertime North Atlantic storm track regimes and Eastern Mediterranean cyclones and rainfall. To do so, we use different detection algorithms for each element in the chain (RWBs, streamers and cyclones). A cluster analysis of upper tropospheric eddy kinetic energy reveals a favorable configuration of the storm track where North Atlantic storms are able to propagate farther northeast. This results in upper-level potential vorticity streamers forming more eastward alongside above-average precipitation over the Levant. Meanwhile, other latitudinal positions of the storm track (southward or northward) were found to hinder cyclonic activity in the region and reduce rainfall there. The intense rainy winter of 1991–1992 is brought as a test case to exemplify this mechanism in its extreme. We show that the rain-enhancing storm track regime was prominent throughout most of this season, alongside frequent streamers in the Eastern Mediterranean.

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Dor Sandler, Hadas Saaroni, Baruch Ziv, Talia Tamarin-Brodsky, and Nili Harnik

Status: open (until 22 May 2024)

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  • RC1: 'Comment on egusphere-2024-1054', Emmanouil Flaounas, 19 Apr 2024 reply
  • RC2: 'Comment on egusphere-2024-1054', Anonymous Referee #2, 09 May 2024 reply
Dor Sandler, Hadas Saaroni, Baruch Ziv, Talia Tamarin-Brodsky, and Nili Harnik
Dor Sandler, Hadas Saaroni, Baruch Ziv, Talia Tamarin-Brodsky, and Nili Harnik


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Short summary
The North Atlantic region serves as a source of moisture and energy for Mediterranean storms. Its impact over the Levant region remains an open question due to its smaller weather systems and their longer distance from the ocean. We find an optimal circulation pattern which allows North Atlantic influence to reach farther into the Eastern Mediterranean, thus making storms stronger and rainier. This may be relevant for future Mediterranean climate, which is projected to become much drier.