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Vertical velocity and turbulence aspects during Mistral events as observed by UHF wind profilers

Authors :
V. Guénard
Bruno Benech
Bernard Campistron
Jean-Luc Caccia
P. Drobinski
Laboratoire de sondages électromagnétiques de l'environnement terrestre (LSEET)
Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS)
Laboratoire d'aérologie (LAERO)
Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP)
Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3)
Université Fédérale Toulouse Midi-Pyrénées
Institut Pierre-Simon-Laplace (IPSL)
École normale supérieure - Paris (ENS Paris)
Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)
Université Toulouse III - Paul Sabatier (UT3)
Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP)
Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3)
Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
École normale supérieure - Paris (ENS-PSL)
Source :
Annales Geophysicae, Annales Geophysicae, European Geosciences Union, 2004, 22 (11), pp.3927-3936, Annales Geophysicae, Vol 22, Pp 3927-3936 (2004), Annales Geophysicae, Vol 22, Iss 11, Pp 3927-3936 (2004), Annales Geophysicae, 2004, 22 (11), pp.3927-3936
Publication Year :
2004
Publisher :
HAL CCSD, 2004.

Abstract

The general purpose of this paper is to experimentally study mesoscale dynamical aspects of the Mistral in the coastal area located at the exit of the Rhône-valley. The Mistral is a northerly low-level flow blowing in southern France along the Rhône-valley axis, located between the French Alps and the Massif Central, towards the Mediterranean Sea. The experimental data are obtained by UHF wind profilers deployed during two major field campaigns, MAP (Mesoscale Alpine Program) in autumn 1999, and ESCOMPTE (Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transports d'Emission) in summer 2001. Thanks to the use of the time evolution of the vertical profile of the horizontal wind vector, recent works have shown that the dynamics of the Mistral is highly dependent on the season because of the occurrence of specific synoptic patterns. In addition, during summer, thermal forcing leads to a combination of sea breeze with Mistral and weaker Mistral due to the enhanced friction while, during autumn, absence of convective turbulence leads to substantial acceleration as low-level jets are generated in the stably stratified planetary boundary layer. At the exit of the Rhône valley, the gap flow dynamics dominates, whereas at the lee of the Alps, the dynamics is driven by the relative contribution of "flow around" and "flow over" mechanisms, upstream of the Alps. This paper analyses vertical velocity and turbulence, i.e. turbulent dissipation rate, with data obtained by the same UHF wind profilers during the same Mistral events. In autumn, the motions are found to be globally and significantly subsident, which is coherent for a dry, cold and stable flow approaching the sea, and the turbulence is found to be of pure dynamical origin (wind shears and mountain/lee wave breaking), which is coherent with non-convective situations. In summer, due to the ground heating and to the interactions with thermal circulation, the vertical motions are less pronounced and no longer have systematic subsident charateristics. In addition, those vertical motions are found to be much less developed during the nighttimes because of the stabilization of the nocturnal planetary boundary layer due to a ground cooling. The enhanced turbulent dissipation-rate values found at lower levels during the afternoons of weak Mistral cases are consistent with the installation of the summer convective boundary layer and show that, as expected in weaker Mistral events, the convection is the preponderant factor for the turbulence generation. On the other hand, for stronger cases, such a convective boundary layer installation is perturbed by the Mistral.

Details

Language :
English
ISSN :
09927689 and 14320576
Database :
OpenAIRE
Journal :
Annales Geophysicae, Annales Geophysicae, European Geosciences Union, 2004, 22 (11), pp.3927-3936, Annales Geophysicae, Vol 22, Pp 3927-3936 (2004), Annales Geophysicae, Vol 22, Iss 11, Pp 3927-3936 (2004), Annales Geophysicae, 2004, 22 (11), pp.3927-3936
Accession number :
edsair.doi.dedup.....a4a63e0b4beaeedef323a8b421b8dc3c