National Center of Meteorological Researches
42, av. Coriolis
Cities are the location for a microclimate whose main characteristic is an urban heat island (UHI). Its consequences on the comfort of city-dwellers have long been known. In 1885, Guy de Maupassant describes, in his book Bel Ami, Parisians frequently visiting nature parks in search of coolness so as to get away from the unbearable heat of the city! Compared to the violence of a cyclone, of a storm or thunderstorm, the concern for urban comfort seems to be a trivial issue. Yet, this microclimate affects the health of the populations mainly because of the increase in thermal stress that the human body has to confront. The consequences were quite severe during the 2003 heat wave and victims were proportionately more numerous in the city where evening temperatures failed to decrease below 25 °C. In this field, my focus is on the analysis of the urban climate in relation to the variation the urban properties to evaluate which have the largest influence.
A UHI is a phenomenon that affects the lower layers of the atmosphere; thus, exchanges of energy and mass for an urban surface are elementary processes that need to be characterized. The energy balance equation for a surface reflects the balance between energy sources and energy sinks. The first energy source of any land surface is the net radiation (balance of solar and infrared radiation). In urban areas, the anthropogenic heat releases by human activities (traffic, air conditionning, industries...) are specific sources of energy. The energy sinks are as for any other land surface the convective heat flux and the latent heat flux. Moreover, since the urban surface is far from flat and homogeneous and the rough components have large dimensions, the energy balance is estimated for a control volume extending from ground level to the top of buildings. Thus, two other sinks are taken into account: the heat storage inside the control volume (including buildings materials) and the advection through the boundaries of the control volume. On this point, my research has been conducted more specifically on the estimation of the anthropogenic contribution and the advection of heat.
During the CAPITOUL experiment that took place over Toulouse from March 2004 to March 2005, I focused my research on the estimation of the anthropogenic heat releases by the human activites. I did it with the measurements of the classical terms of the energy balance in the city center and an inventory of energy consumption all over the urban area. At the city center, both methods gave very similar results and it appeared that during winter, the anthropogenic heat releases were up to 100 W m-2. They are almost making up the deficit of solar energy during this period of the year ! After having demonstrated the capability of the Town Energy Budget model (TEB, Masson, 2000) to reproduce this term during fall and winter, my objective is now to improve the description of the building in TEB and more specifically, to include a parameterization of the air cooling systems.
Richard, E., Flamant, C., Bouttier, F., Baelen, J. V., Champollion, C., Argence, S., Arnault, J., Barthlott, C., Behrendt, A., Bosser, P., Brousseau, P., Chaboureau, J.-P., Corsmeier, U., Cuesta, J., Girolamo, P. D., Hagen, M., Kottmeier, C., Limnaios, P., Masson, F., Pigeon, G., Pointin, Y., Seity, Y. and Wulfmeyer, V. "La campagne COPS : initiation et cycle de vie de la convection en région montagneuse," La Météorologie (64), 2009.
Hidalgo, J., Masson, V., Baklanov, A., Pigeon, G. and Gimeno, L. "Advances in Urban climate modelling," Annals of the New York Academy of Sciences (Volume 1146), 2008, pp. 354-374.
Hidalgo, J., Masson, V. and Pigeon, G. "Urban-Breeze Circulation during the CAPITOUL experiment: Numerical simulations," Meteorology and Atmospheric Physics (102), 2008, pp. 243-262.
Hidalgo, J., Pigeon, G. and Masson, V. "Urban-Breeze Circulation during the CAPITOUL Experiment: observational data Analysis Approach," Meteorology and Atmospheric Physics (102), 2008, pp. 223-241.
Masson, V., Gomes, L., Pigeon, G., Liousse, C., Pont, V., Lagouarde, J.-P., Voogt, J., Salmond, J., Oke, T. R., Hidalgo, J., Legain, D., Garrouste, O., Lac, C., Connan, O., Briottet, X., Lachérade, S. and Tulet, P. "The Canopy and Aerosol Particles Interactions in TOulouse Urban Layer (CAPITOUL) experiment," Meteorology and Atmospheric Physics (102:3), 2008, pp. 135--157.
Pigeon, G., Lemonsu, A., Masson, V. and Hidalgo, J. "De l'observation du micro-climat urbain à la modélisation intégrée de la ville," La Météorologie (62), 2008, pp. 39-47.
Pigeon, G., Moscicki, M. A., Voogt, J. A. and Masson, V. "Simulation of fall and winter surface energy balance over a dense urban area using the TEB scheme," Meteorology and Atmospheric Physics (102:3), 2008, pp. 159--171.
Pigeon, G., Legain, D., Durand, P. and Masson, V. "Anthropogenic heat releases in an old European agglomeration (Toulouse, France).," International Journal of Climatology (27), 2007, pp. 1969-1981.
Pigeon, G., Lemonsu, A., Grimmond, C., Durand, P., Thouron, O. and Masson, V. "Divergence of turbulent fluxes in the surface layer: case of a coastal city," Boundary-Layer Meteorol. (124), 2007, pp. 269-290.
Lemonsu, A., Pigeon, G., Masson, V. and Moppert, C. "Sea-town interactions over Marseille: 3D urban boundary layer and thermodynamic fields near the surface," Theor. and Appl. Climatol. (84:6), 2006, pp. 171-178.
Pigeon, G., Lemonsu, A., Long, N., Barrié, J., Durand, P. and Masson, V. "Urban thermodynamic island in a coastal city analyzed from an optimized surface network," Boundary-Layer Meteorol. (120), 2006, pp. 315-351.
Mestayer, P. G., 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, C. S. B., 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. R., Pigeon, G., Puygrenier, V., Roberts, S., Rosant, J. M., Saïd, F., Salmond, J., Talbaut, M. and Voogt, J. "The Urban Boundary-Layer Field Campaign in Marseille (UBL/CLU-Escompte): Set-Up and First Results.," Boundary-Layer Meteorol. (114), 2005, pp. 315-365.
Puygrenier, V., Lohou, F., Campistron, B., Saïd, F., Pigeon, G., Benech, B. and Serça, D. "Investigation on the fine structure of sea-breeze during ESCOMPTE experiment.," Atmos. Res. (74), 2005, pp. 329-353.