Vertical Structure of the Urban Boundary Layer over Marseille Under Sea-Breeze Conditions
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During the UBL-ESCOMPTE program (June–July 2001), intensive observations were performed in Marseille (France). In particular, a Doppler lidar, located in the north of the city, provided radial velocity measurements on a 6-km radius area in the lowest 3 km of the troposphere. Thus, it is well adapted to document the vertical structure of the atmosphere above complex terrain, notably in Marseille, which is bordered by the Mediterranean sea and framed by numerous massifs. The present study focuses on the last day of the intensive observation period 2 (26 June 2001), which is characterized by a weak synoptic pressure gradient favouring the development of thermal circulations. Under such conditions, a complex stratification of the atmosphere is observed. Three-dimensional numerical simulations, with the Méso-NH atmospheric model including the town energy balance (TEB) urban parameterization, are conducted over south-eastern France. A complete evaluation of the model outputs was already performed at both regional and city scales. Here, the 250-m resolution outputs describing the vertical structure of the atmosphere above the Marseille area are compared to the Doppler lidar data, for which the spatial resolution is comparable. This joint analysis underscores the consistency between the atmospheric boundary layer (ABL) observed by the Doppler lidar and that modelled by Méso-NH. The observations and simulations reveal the presence of a shallow sea breeze (SSB) superimposed on a deep sea breeze (DSB) above Marseille during daytime. Because of the step-like shape of the Marseille coastline, the SSB is organized in two branches of different directions, which converge above the city centre. The analysis of the 250-m wind fields shows evidence of the role of the local topography on the local dynamics. Indeed, the topography tends to reinforce the SSB while it weakens the DSB. The ABL is directly affected by the different sea-breeze circulations, while the urban effects appear to be negligible.
KeywordsAtmospheric boundary layer Doppler lidar Numerical simulation Sea breezes Topography
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- Bastin S., Drobinski P., Dabas A., Delville P., Reitebuch O. and Werner C. (2004). ‘Sea Breeze Case Study using a Combination of Observations and Numerial Stimulation in Complex Terrain in Southern France: Contribution to Matter Transport’. Mt Washington Valley, New Hampshire, USAGoogle Scholar
- Calhoun R., Heap R. B., Princevac M., Sommer J., Fernando H. J. S. and Ligon D. (2004). ‘Measurement of Winds Flowing Toward an Urban Area Using Coherent Doppler Lidar’. Fifth Conference on Urban Environment Vancouver, CanadaGoogle Scholar
- CEC (1993). ‘CORINE Land Cover, Technical Guide’. Office for the Official Publications of the European Communities, LuxembourgGoogle Scholar
- Deardorff J. W. (1974). ‘Three-Dimensional Numerical Study of Turbulence in an Entraining Mixed Layer’. Boundary-Layer Meteorol. 7: 199–126Google Scholar
- Dousset B. and Kermadi S. (2003). ‘Satellites Observation over the Marseille-Berre Area during the UBL/CLU-ESCOMPTE Experiment’. Lódź, PolandGoogle Scholar
- Drobinski, P., Bastin, S., Dusek, J., Zängl, G., and Flamant, P. H.: 2005b, ‘Idealized Simulations of Flow Splitting at the Bifurcation Between Two Valleys: Comparison with the Mesoscale Alpine Program Experiment’, Meteorol. Atmos. Phys., in press.Google Scholar
- Lafore J.-P., Stein J., Asencio N., Bougeault P., Ducrocq V., Duron J., Fischer C., Héreil P., Mascart P., Masson V., Pinty J.-P., Redelsperger J.-L., Richard E. and Vilà-Gueraude Arellano J. (1998). ‘The Meso-Nh atmospheric simulation system Part I: Adiabatic Formulation and Control Simulation’. Ann. Geophys. 16: 90–109CrossRefGoogle Scholar
- Lemonsu, A., Pigeon, G., Masson, V., and Moppert, C.: 2005, ‘Sea-Town Interaction over Marseille: 3D Urban Boundary Layer and Thermodynamic Fields near the Surface’, Theor. Appl. Clim., in press.Google Scholar
- Mestayer P., Durand P., Augustin P., Bastin S., Bonnefond J.-M., Bénech B., Campistron B., Coppalle A., Delbarre H., Dousset B., Drobinski P., Druilhet A., Fréjafon E., Grimmond S., Groleau D., Irvine M., Kergomard C., Kermadi S., Lagouarde J.-P., Lemonsu A., Lohou F., Long N., Masson V., Moppert C., Noilhan J., Offerle B., Oke T., Pigeon G., Puygrenier V., Roberts S., Rosant J.-M., Saïd F., Salmond J., Talbaut M. and Voogt J. (2005). ‘The Urban Boundary Layer Field Experiment over Marseille UBL/CLU-ESCOMPTE: Experimental Set-up and First Results’. Boundary-Layer Meteorol. 114: 315–365CrossRefGoogle Scholar
- Physick W. L. and Byron-Scott R. A. D. (1977). ‘Observations of the Sea Breeze in the Vicinity of a Gulf’. Weather 32: 373–381Google Scholar