Research On The Improvement Of Meteorological Simulation In Beijing Using Planetary Boundary Layer Parameterization Scheme And Fine-scale Urban Underlying Surface Data

In this paper,the Weather Research and Forecasting Model is used to simulate the effects of planetary boundary layer parameterization schemes and fine-scale urban underlying surface on near-surface meteorological elements and boundary layer structure in Beijing under short-term and long-term weather conditions.In addition,we improved the urban canopy parameters to make the simulated 2 m temperature better.Firstly,we choose 02:00 on October 1 to 08:00 on October 4,2018 as the simulation period.The research goal of this part is to analyse the effects of YSU(Yonsei University Scheme),ACM2(Asymmetric Convective Model 2 Scheme),MYJ(Mellor-YamadaJanjic Scheme),and BL(Bougeault-Lacarrere PBL)boundary layer parameterization schemes on atmospheric radiation flux,surface energy flux,near-surface meteorological elements and urban boundary layer structure in Beijing.Subsequently,the Local Climate Zone(LCZ)maps of Beijing in 2006 and 2018 are established.The LCZ maps subdivide the urban surface into 10 types to accurately describe the urban morphological characteristics and thermal environment.Based on the study of planetary boundary layer parameterization schemes,the single-layer urban canopy model(SLUCM)is coupled to WRF to simulate the differences between the 2018 LCZ map and MODIS land use data in the simulated temperature results,and the urban fraction and emissivity parameters in the urban canopy parameter table are improved to optimize the temperature simulation results.Finally,LCZ maps of 2006 and 2018 are used as the underlying surface static data for WRF input,and two months in winter and summer are chosen as simulation periods to research the urbanization effect on the local meteorological field in Beijing.The specific results are as follows:(1)The YSU,ACM2,MYJ,and BL schemes have little influence on short-wave and long-wave radiation fluxes;The YSU boundary layer parameterization scheme can better simulate the near-surface meteorological elements and boundary layer structure of Beijing during the clear weather process.For the boundary layer structure,the temperature profile simulated by YSU scheme is closest to the observation,and all kinds of PBL schemes can simulate the variation characteristics of the wind speed profile.(2)Compared with SLAB scheme,WRF model coupled with SLUCM can better reflect urban local climate.The 2018 LCZ map is used to replace MODIS urban underlying surface data,which can better simulate the local temperature difference characteristics.The simulated temperature results are closely related to urban land cover types.For example,the temperature ranges of open and compact low-rise areas(LCZ3,6)are lower,the night temperature of the low-rise building is lower than that of mid-rise and high-rise buildings.The temperature range of sparsely built(LCZ9)is the lowest.(3)The improvement of urban fraction and emissivity parameters in the urban canopy parameter table can improve the temperature simulation results,and the improvement effect at night is more obvious than that in the daytime.(4)The growth of urban area will lead to the rise of near-surface temperature,and the decrease of humidity and wind speed,etc.The area with high building density and low building height has a larger heat storage capacity.The open mid-rise area(LCZ5)has the highest heat storage capacity,while the sparsely built area(LCZ9)has a weaker heat storage capacity,relatively rapid energy exchange,and fast heating and cooling.In this paper,based on the study of the effect of PBL schemes and fine-scale urban underlying surface on simulation meteorological field,aiming at the problem of temperature simulation errors,we modified the urban parameters to improve simulation precision.We also explored the effect of land-use change based on urbanization on the local meteorological conditions,providing the basis for future urban climate research.