Numerical Simulation Study On The Impact Of Urban Surface On Average Meteorological Elements In Beijing

This paper focuses on simulating the impact of urban surface on average meteorological elements in Beijing winter&summer by two approaches. After analyzing the mean meteorological elements distribution characteristics in Jan and Jul2012,we use WRF modeling system to simulate the mean air temperature and humidity at2m height, mean wind speed at10m height by two approaches based on circulation type classification:One is simulating all cases then average the outputs (called the cases-averaged method) and the other is using the averaged NCEP-FNL data as mean initial and lateral boundary conditions for the model to simulate average meteorological elements of different circulation types (the mean-field method). Then the results of two methods under new and old land use conditions are evaluated against the observation. At last, the analysis of affect caused by urban development and the comparison of two methods for reflecting this affect are carried out.The performance showed that cases-averaged method has a good simulation results for Jan and Jul2012than mean-field method, Simulating results of undefined circulation type (UD type) is better than cyclone circulation type(C type) in Jul; The characteristics of month-averaged meteorological elements spatial distribution and diurnal variation simulated by two methods are consistent good in winter. Hite rates of air temperature and wind speed are higher than60%in Jan by mean-field approach. It has reasonable results of air temperature and wind speed for UD type than specific humidity in summer, but may not simulates the mean elements of C type.Urbanization slightly decreases the specific humidity and wind speed but increases the air temperature at night than day in winter. The impacts of temperature and wind speed for C type are bigger than UD type, which are1.13℃and-1.14m/s in Jul night simulated by cases-average approach; Mean-field method has a feasibility of assessing urban impact on average wind speed and temperature in winter for UD type in Jul, it reflects the impacts of urban surface on air temperature and wind speed at daytime but not the specific humidity decrease. The cases-averaged method not only reflects the average impact of urban development but also simulates the extreme impact. The mean-field method may not get good impact on average meteorological elements for C type, extreme impact conditions and precipitation simulation.