Urbanization of mesoscale models
Description
This dissertation addresses two important aspects of urbanization of mesoscale models: urban short-wave radiation budget and anthropogenic heat emission in urban areas. An urban canopy radiation model was developed to take into account the diurnal variation of short-wave radiation, including the effects of surface shading and multiple reflections within urban canyons. This model is able to calculate the time-dependent effective albedo as well as the daily mean energy-weighted albedo for any urban domain. Monte Carlo style simulations for four typical urban land use categories indicate that the traditional nadir-view albedo overestimates the reflected short-wave radiation from a city by 11--26%. With the Monte Carlo ensemble method, this radiation model also can provide the statistical mean urban albedo for urban mesoscale modeling The effect of anthropogenic heating (Qf) was incorporated into the MM5 mesoscale atmospheric model. Several typical release cases of anthropogenic heat in the urban environment were considered. With respect to the multiple Planetary Boundary Layer (PBL) scheme options available within the MM5 modeling systems, we have enabled Q f within two commonly used PBL modules---Blackadar and Gayno-Seaman. They have different vertical mixing mechanisms in the daytime convective PBL. The Blackadar scheme was modified in this study to improve its performance during the morning transition. Case study simulations for Philadelphia and Atlanta were performed to investigate the impacts of anthropogenic heating on Urban Heat Island (UHI) development. Results suggest that anthropogenic heating plays an important role in the UHI formation, particularly during night and winter. In addition, anthropogenic heating was also found to have impacts on the nocturnal atmospheric PBL stability and PBL structure during morning transition