Evaluation of the Weather Research and Forecast/Urban Model Over Greater Paris

Abstract

Meteorological modelling in the planetary boundary layer (PBL) over Greater Paris is performed using the Weather Research and Forecast (WRF) numerical model. The simulated meteorological fields are evaluated by comparison with mean diurnal observational data or mean vertical profiles of temperature, wind speed, humidity and boundary-layer height from 6 to 27 May 2005. Different PBL schemes, which parametrize the atmospheric turbulence in the PBL using different turbulence closure schemes, may be used in the WRF model. The sensitivity of the results to four PBL schemes (two non-local closure schemes and two local closure schemes) is estimated. Uncertainties in the PBL schemes are compared to the influence of the urban canopy model (UCM) and the updated Coordination of Information on the Environment (CORINE) land-use data. Using the UCM and the CORINE land-use data produces more realistic modelled meteorological fields. The wind speed, which is overestimated in the simulations without the UCM, is improved below 1,000 m height. Furthermore, the modelled PBL heights during nighttime are strongly modified, with an increase that may be as high as 200 %. At night, the impact of changing the PBL scheme is lower than the impact of using the UCM and the CORINE land-use data.

The role of urban boundary layer investigated with high-resolution models and ground-based observations in Rome area: a step towards understanding parameterization potentialities

“…associated with the urban category have been considered representative, on average, of the Rome environment. These are in line with settings of Kim et al (2013) for the city of Paris. The largest difference is found for roof width and anthropogenic heat flux (AH); the first one, set by default at 9.4 m (3.75 m for Paris), is close to a realistic average between the roof of the building where instruments site is located and surroundings ones.…”

“…The results for the WRF model simulations presented in this paper show similarities to those for previous studies in other urban areas performed both with WRF (Hu et al, 2010;Salamanca et al, 2011;Flagg and Taylor, 2011;Kim et al, 2013) and with other models (Wouters et al, 2013). Kim et al (2013) in a study over Paris area show WRF overestimation of horizontal wind speed in a weak wind regime, regardless of the PBL scheme used, but with MYJ producing the largest mean biases.…”

“…Recently, the new generations of high-resolution NWP models have also been applied to urban areas for both weather forecast and research purposes (Grossman-Clarke et al, 2008;Salamanca et al, 2011Salamanca et al, , 2012Flagg and Taylor, 2011;Kim et al, 2013;Wouters et al, 2013). Generally, these areas are covered by dry materials (asphalt or concrete) and are warmer and drier than adjacent rural areas (Oke, 1982); the efficiency of the urban areas in storing heat can produce remarkable mesoscale perturbations of the lower layers of the atmosphere (by variations of wind, temperature and water vapor content).…”

“…Generally, these areas are covered by dry materials (asphalt or concrete) and are warmer and drier than adjacent rural areas (Oke, 1982); the efficiency of the urban areas in storing heat can produce remarkable mesoscale perturbations of the lower layers of the atmosphere (by variations of wind, temperature and water vapor content). The inclusion of urban effects in NWP models can, thus, significantly improve the weather forecast (Kim et al, 2013). Featuring the urban boundary layer adds a further complexity that is usually resolved by coupling PBL schemes with urban canopy parameterizations inside models.…”

“…The Mellor-Yamada-Janjic (MYJ, Mellor and Yamada, 1982) scheme has been chosen as TKE closure scheme; this is one of the most-used schemes and it can also be coupled with the multilayer canopy model available with WRF . It has indeed been shown (Flagg and Taylor, 2011;Lee et al, 2011;Kim et al, 2013;Martilli, 2002) that an appropriate explicit parametrization of urban physical processes produces more accurate results in other urban areas. Based on the previous considerations, the sensitivity to the surface layer of the two PBLs is also investigated in order to highlight their role in influencing the PBL inside and outside the Rome urban area.…”