Urban parameterization schemes into MM5 model
Dandou, A., Akylas, E., Tombrou, M.
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract 10882
In the last few years, several efforts have been made in order to improve the representation of urban surface characteristics in mesoscale models. In general, attempts have been made either to improve the ‘thermal’ part (impact on the heat fluxes) or the ‘dynamical’ part (impact on the wind field and the turbulent kinetic energy). The objective is to improve the quantification of the fluxes associated with heat storage change and to account more explicitly for the integrated effect of urban canopy layer fluxes on the overlaying boundary layer. This modification is very important, since pollutant dispersion is strongly dependent on the structure of the urban boundary layer and on its interactions with the rural boundary layer and the synoptic flow. In the present study, the MM5 model (Penn State/NCAR Mesoscale Model, Anthes et al., 1978) was modified, by considering recent advances in the planetary boundary layer. In particular, the modifications were carried out in two directions; a) the surface stress and fluxes of heat and momentum were parameterized for use of the MM5 model with emphasis laid on unstable conditions. The key quantities in these parameterizations are the PBL height and the convective velocity scale W*. In addition, the Kansas-type functions were modified in order to satisfy the free convection limit which is particularly important in cases with larger roughness lengths; and (b) with respect to the thermal properties of an urban surface, the surface energy balance was modified by taking into account the anthropogenic heat released in urban areas and the urban heat storage term, to account for urban/building mass effect, including hysteresis. These modifications were applied to the high resolution non-local MRF PBL parameterization scheme, based on Troen and Marht. Numerical simulations were carried out for the Greater Athens area. The modifications mentioned above, produce minor changes to the wind field, but they enhance the value of friction velocity up to 25% during strong instability over very rough surfaces and the diffusion coefficients, up to a proportion of 30%, depending on the intensity of the instability. Moreover, they enhance the temperature’s diurnal range. These enhancements affect the pollutants deposition velocity and consequently the pollutants dispersion in the atmosphere.
Dandou, A., Akylas, E., Tombrou, M.
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract 10882
In the last few years, several efforts have been made in order to improve the representation of urban surface characteristics in mesoscale models. In general, attempts have been made either to improve the ‘thermal’ part (impact on the heat fluxes) or the ‘dynamical’ part (impact on the wind field and the turbulent kinetic energy). The objective is to improve the quantification of the fluxes associated with heat storage change and to account more explicitly for the integrated effect of urban canopy layer fluxes on the overlaying boundary layer. This modification is very important, since pollutant dispersion is strongly dependent on the structure of the urban boundary layer and on its interactions with the rural boundary layer and the synoptic flow. In the present study, the MM5 model (Penn State/NCAR Mesoscale Model, Anthes et al., 1978) was modified, by considering recent advances in the planetary boundary layer. In particular, the modifications were carried out in two directions; a) the surface stress and fluxes of heat and momentum were parameterized for use of the MM5 model with emphasis laid on unstable conditions. The key quantities in these parameterizations are the PBL height and the convective velocity scale W*. In addition, the Kansas-type functions were modified in order to satisfy the free convection limit which is particularly important in cases with larger roughness lengths; and (b) with respect to the thermal properties of an urban surface, the surface energy balance was modified by taking into account the anthropogenic heat released in urban areas and the urban heat storage term, to account for urban/building mass effect, including hysteresis. These modifications were applied to the high resolution non-local MRF PBL parameterization scheme, based on Troen and Marht. Numerical simulations were carried out for the Greater Athens area. The modifications mentioned above, produce minor changes to the wind field, but they enhance the value of friction velocity up to 25% during strong instability over very rough surfaces and the diffusion coefficients, up to a proportion of 30%, depending on the intensity of the instability. Moreover, they enhance the temperature’s diurnal range. These enhancements affect the pollutants deposition velocity and consequently the pollutants dispersion in the atmosphere.