On the Interaction between Sea Breeze and Summer Mistral at the Exit of the Rhône Valley

Abstract

The three-dimensional structure and dynamics of the combination of the sea breeze and the mistral at the Rhône Valley exit, in southeastern France, have been investigated experimentally and numerically on 22 June 2001. The mistral refers to a severe northerly wind that develops along the Rhône Valley. The exit of this valley is located near the Mediterranean Sea where sea-breeze circulation often develops. The sea breeze and the mistral coexist this day because of the weakness of this mistral event. The event was documented in the framework of the Expérience sur Site pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d'Emissions (ESCOMPTE) field experiment. Several important data sources are used (airborne Doppler lidar, UHF wind profilers, radiosoundings, and surface stations) as well as nonhydrostatic mesoscale simulations. This paper examines the various mechanisms that drive the time and spatial variability of the mistral and the sea breeze in various regions of the Rhône Valley. In the morning, the sea breeze penetrates inland near the western side of the Rhône Valley then moves back because of the reinforcement of the mistral flow caused by the deepening of the leeward surface low due to convection at noon. At midday, the sea breeze penetrates inland in the middle of the Rhône Valley only. In contrast to pure sea-breeze episodes when the sea breeze can extend inland over a horizontal range of more than 150 km, the presence of the mistral prevents the sea breeze from penetrating more than 40 km onshore. In the late afternoon, the sea breeze reaches the eastern side of the Rhône Valley but over a smaller horizontal range because of higher local topography and because the mistral is more intense in this part of the Rhône Valley. The situations of sea-breeze–mistral interactions can have a severe impact on regional air quality. Indeed, the southerly sea breeze, which advects toward the countryside the pollutants emitted from the large coastal city of Marseille, France, and its industrialized suburbs, cannot penetrate far inland because of the mistral blowing in the opposite direction. This leads to the stagnation of the pollutants near the area of emission that is also the most densely inhabited area of the region (over one million inhabitants)

Sea‐breeze‐induced mass transport over complex terrain in south‐eastern France: A case‐study

“…The results should thus apply at least qualitatively (quantitatively, the results depend on the strength of the synoptic flow) to the combination of the sea breeze with moderate Mistral observed during IOP2a (21 to 23 June 2001) (Bastin et al 2005b(Bastin et al , 2006 or the 4 July 2001 event of IOP3 (see Cros et al 2004 for a description of the IOP meteorological conditions).…”

Mistral and Tramontane wind speed and wind direction patterns in regional climate simulations

“…Several case studies have been performed on Mistral events Drobinski et al 2005) and their interaction with sea breezes (Bastin et al 2006) and heavy precipitation events (Berthou et al 2014(Berthou et al , 2015. Tramontane events have also been studied (Drobinski et al 2001).…”

Aerosol distribution over the western Mediterranean basin during a Tramontane/Mistral event

“…The Mistral occurs all year long but exhibits a seasonal variability either in terms of its strength and direction, or in terms of its spatial distribution (Mayençon, 1982;Orieux and Pouget, 1984). At the regional scale, the Mistral is frequently observed to extend as far as a few hundred kilometers from the coast (Jansá, 1987) and is thus associated with low continental pollution levels near the coastline as it advects the pollutants away from their sources of emission over the Mediterranean Sea (Bastin et al, 2006;Drobinski et al, 2007).…”

“…The 24 March 1998 Mistral/Tramontane case is a strong episode, typical of intermediate season Mistral events compared to weaker summer Mistral events (e.g. Drobinski et al, 2005;Bastin et al, 2006). Flamant (2003) analyzed the complex structure of the atmospheric boundary layer (ABL) observed using an airborne lidar over the Gulf of Lion during the 24 March 1998 Mistral event (see Fig.…”