Atmos. Chem. Phys. Discuss., 12, 25941-25981, 2012
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The diurnal evolution of the urban heat island of Paris: a model-based case study during Summer 2006
H. Wouters1,2, K. De Ridder1, N. P. M. van Lipzig2, M. Demuzere2, and D. Lauwaet1
1VITO Flemish Institue for Technological Research, Dept. Environmental and Atmospheric Modelling, Mol, Belgium
2KU Leuven, dept. Earth and Environmental Sciences, Leuven, Belquim

Abstract. The urban heat island (UHI) over Paris during summer 2006 was simulated using the Advanced Regional Prediction System (ARPS) updated with a simple urban parametrization at a horizontal resolution of 1 km. Two integrations were performed, one with the urban land cover of Paris and another in which Paris was replaced by cropland. The focus is on a five-day clear-sky period, for which the UHI intensity reaches its maximum. The diurnal evolution of the UHI intensity was found to be adequately simulated for this five day period. The maximum difference at night in 2-m temperature between urban and rural areas stemming from the urban heating is reproduced with a relative error of less than 10%. The UHI has an ellipsoidal shape and stretches along the prevailing wind direction. The maximum UHI intensity of 6.1 K occurs at 23:00 UTC located 6 km downstream of the city centre and this largely remains during the whole night. An idealized one-column model study demonstrates that the nocturnal differential sensible heat flux, even though much smaller than its daytime value, is mainly responsible for the maximum UHI intensity. The reason for this nighttime maximum is that additional heat is only affecting a shallow layer of 150 m. At the same time, an idealized study shows that the orography around the city of Paris induces an uplift. This leads to a considerable nocturnal adiabatic cooling over cropland. In contrast, this uplift has little effect on the mixed-layer temperature over the city. About twenty percent of the total maximum UHI intensity is estimated to be caused by this uplift.

Citation: Wouters, H., De Ridder, K., van Lipzig, N. P. M., Demuzere, M., and Lauwaet, D.: The diurnal evolution of the urban heat island of Paris: a model-based case study during Summer 2006, Atmos. Chem. Phys. Discuss., 12, 25941-25981, doi:10.5194/acpd-12-25941-2012, 2012.
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