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The influence of a mega-city on the atmospheric boundary layer wind field was examined in the complex-terrain, semi-arid Tehran region using the Pennsylvania State University/National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) during a high pollution period. In addition, model sensitivity studies were conducted to evaluate the performance of the urban canopy and urban soil model "SM2-U (3D)" parameterization on the wind field. The topographic flows and urban effects were found to play important roles in modulating the wind field, and the urbanized areas exerted important local effects on the boundary layer meteorology. An emission inventory of heat generation was developed and updated for 2005 in this work. By using a detailed methodology, we calculated spatial and temporal distributions of the anthropogenic heat flux (Qf) for Tehran during 2005. Wintertime Qf is found larger than summertime Qf, which reflects the importance of heating emissions from buildings and traffic during cold and warm periods respectively. Different urban parameterizations were used as a tool to investigate the modifications induced by the presence of an urban area in the area of interest. It is found that, for local meteorological simulations, the drag-force approach (DA) coupled with an urban soil model (SM2-U) is preferable to the roughness approach (RA) coupled with a slab soil model. The comparisons indicated that the most important features of the wind field, in urban areas are well reproduced by the DA-SM2-U configuration with the anthropogenic heat flux being taken into account. This modeling option showed that the suburban part of the city is dominated by topographic flows whereas the center and south of Tehran are more affected by urban heat island (UHI) forcing especially during the night in studied episodes.

A Modeling Study of Boundary Layer Wind Flow over Tehran Region during a High Pollution Episode