Preprints
https://doi.org/10.5194/wcd-2021-7
https://doi.org/10.5194/wcd-2021-7

  29 Jan 2021

29 Jan 2021

Review status: this preprint is currently under review for the journal WCD.

Synoptic-scale drivers of the Mistral wind: link to Rossby wave life cycles and seasonal variability

Yonatan Givon1, Douglas Keller Jr.2, Romain Pennel2, Philippe Drobinski2, and Shira Raveh-Rubin1 Yonatan Givon et al.
  • 1Department of Earth and Planetary Sciences, Weizmann Institute of Science
  • 2Laboratoire de Météorologie Dynamique - IPSL, École Polytechnique, Institut Polytechnique de Paris, ENS, PSL Research University, Sorbonne Université, CNRS, Palaiseau France

Abstract. The mistral is a northerly low level jet blowing through the Rhône valley in southern France, and down to the Gulf of Lions. It is co-located with the cold sector of a low level lee-cyclone in the Gulf of Genoa, behind an upper level trough north of the Alps. The mistral wind has long been associated with extreme weather events in the Mediterranean, and while extensive research focused on the low-tropospheric mistral and lee-cyclogenesis, the different upper-tropospheric large- and synoptic-scale settings involved in producing the mistral wind are not generally known. Here, the isentropic potential vorticity (PV) structures governing the occurrence of the mistral wind are classified using a self-organizing map (SOM) clustering algorithm. Based upon a 36-year (1981–2016) mistral database and daily ERA-Interim isentropic PV data, 16 distinct mistral-associated PV structures emerge. Each classified flow pattern corresponds to a different type or stage of the Rossby wave life-cycle, from broad troughs, thin PV streamers, to distinguished cut-offs. Each of these PV patterns exhibit a distinct surface impact in terms of the surface cyclone, surface turbulent heat fluxes, wind, temperature and precipitation. A clear seasonal separation between the clusters is evident and transitions between the clusters correspond to different Rossby wave-breaking processes. This analysis provides a new perspective on the variability of the mistral, and of the Genoa lee-cyclogenesis in general, linking the upper-level PV structures to their surface impact over Europe, the Mediterranean and north Africa.

Yonatan Givon et al.

Status: open (until 24 Mar 2021)

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Yonatan Givon et al.

Yonatan Givon et al.

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Short summary
Mistral wind is a renowned phenomenon in the Mediterranean, yet, its large-scale controlling mechanisms have not been systematically mapped. Here, using a new mistral database for 1981–2016, the upper-tropospheric flow patterns are classified by a self-organizing map algorithm, resulting in 16 distinct patterns related to Rossby wave life cycles. Each pattern has unique surface impact, having implications to understanding mistral predictability, air-sea interaction and their future projections.