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

Abstract

A B S T R A C T 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 22Á23 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.

Scaling precipitation extremes with temperature in the Mediterranean: past climate assessment and projection in anthropogenic scenarios

“…Regarding ocean-atmosphere feedbacks, no sensitivity to the atmosphere-ocean coupling was found on the scaling of precipitation extremes with temperature (not shown). This is not surprising, since atmosphere-ocean feedbacks affect predominantly the location of the precipitating event rather than the intensity Berthou et al 2014Berthou et al , 2015.…”

Lagged effects of the Mistral wind on heavy precipitation through ocean-atmosphere coupling in the region of Valencia (Spain)

“…Most studies of the Western Mediterranean HPEs showed that changes of a few degrees in the upstream SST could modulate precipitation events but in most situations could not drastically change them (Lebeaupin et al 2006;Katsafados et al 2011;Miglietta et al 2011;Berthou et al 2015), except in specific cases: for a squall line on the Balearic islands where SST was determinant in the erosion of an inversion layer ) and a case where the cyclone track was affected and did not land on Calabria anymore (Senatore et al 2014). Lebeaupin Brossier et al (2013) and Berthou et al (2014Berthou et al ( , 2015 showed with regional climate hindcast simulations that HPEs in the Cévennes (southern France) could be modulated by the prior history of Mistral in some cases. However, Berthou et al (2016) showed that cooling of SST by Mistral does not systematically occur before HPEs in the Cévennes.…”

Potential of microwave observations for the evaluation of rainfall and convection in a regional climate model in the frame of HyMeX and MED-CORDEX

“…The precipitation field has been evaluated over land against ECA&D (European Climate Assessment and Data set (Haylock et al, 2008)) and SAFRAN (Système d'analyse fournissant des renseignements atmosphériquesà la neige (QuintanaSeguí et al, 2008)) raingauge-based gridded products at the Mediterranean basin scale (Stéfanon et al, 2014;Lebeaupin-Brossier et al, 2013;Flaounas et al, 2013;Berthou et al, 2014Berthou et al, , 2015 and over sea against the satellite product of the Hamburg Ocean Atmosphere Parameters and fluxes from Satellite data (HOAPS) available twice a day with a spatial resolution of 0.5˚in longitude and latitude . AMSU-B/MHS sounders appear as a complementary approach to evaluate the simulation at finer temporal (3-4 h) and spatial (16 km at nadir) resolutions with an homogeneous precipitation information over land and sea.…”