Prior history of Mistral and Tramontane winds modulates heavy precipitation events in southern France

Abstract

Heavy precipitation events (HPEs) are frequent in southern France in autumn. An HPE results from landward transport of low-level moisture from the Western Mediterranean: large potential instability is then released by local convergence and/or orography. In the upstream zone, the sea surface temperature (SST) undergoes significant variations at the submonthly time scale primarily driven by episodic highly energetic events of relatively cold outflows from the neighbouring mountain ranges (the Mistral and Tramontane winds). Here, we study the HPE of 22–23 September 1994 which is preceded by a strong SST cooling due to the Mistral and Tramontane winds. This case confirms that the location of the precipitation is modulated by the SST in the upstream zone. In fact, changes in latent and sensible heat fluxes due to SST changes induce pressure and stratification changes which affect the low-level dynamics. Using three companion regional climate simulations running from 1989 to 2009, this article statistically shows that anomalies in the HPEs significantly correlate with the SST anomalies in the Western Mediterranean, and hence with the prior history of Mistral and Tramontane winds. In such cases, the role of the ocean as an integrator of the effect of past wind events over one or several weeks does indeed have an impact on HPEs in southern France.

• heavy precipitation events
• Mediterranean
• Mistral
• air–sea interactions
• CORDEX
• atmosphere–ocean coupling

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6. Acknowledgements

This work is a contribution to the HyMeX program (HYdrological cycle in The Mediterranean EXperiment) through INSU-MISTRALS support and the Med-CORDEX program (COordinated Regional climate Downscaling EXperiment Mediterranean region). This research has received funding from the French National Research Agency (ANR) project REMEMBER (contract ANR-12-SENV-001). It was supported by the IPSL group for regional climate and environmental studies, with granted access to the HPC resources of IDRIS (under allocation i2011010227). The authors acknowledge Météo-France who provided the situation description of the 22–23 September 1994 case and observation data (http://pluiesextremes.meteo.fr). We thank the Gruppo di Oceanografia da Satellite team (GOS), http://gos.ifa.rm.cnr.it/index.php, and MYOCEAN project for providing the GOS-SST product.

The authors are very grateful to Robert Jones for his corrections of the English text and to Bénédicte Jourdier for her help with graphism. We thank the anonymous reviewers for their help to improve the manuscript.

Notes

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