Selection And Application Of Optical Combination Of Urban Canopy Models And PBL Parameterization Schemes In WRF Model

To investigate how different planetary boundary layer parameterization schemes and urban canopy models,as well as their combinations in the WRF model,simulate the diurnal variations and vertical structures of meteorological parameters in the urban area of Nanjing City,five regularly used planetary boundary layer schemes(BL,MYL,MYNN,YSU,and SH)and four urban canopy models(noUCM,UCM,BEP,and BEM)were utilized;the simulations were compared to observation data from automated stations and soundings in Nanjing,China,during August 2-3,2015.Then the vertical sounding data from Beijing was used to evaluate the optimal configuration.The following results were obtained.(1)The BL+BEM configuration simulated the 2 m temperature best,as indicated by the root mean square error(RMSE,0.82?).The BL+BEM configuration performed potential temperature profile best both at night(with a correlation coefficient of 0.97 and RMSE of 0.54?)and during the daytime(with a correlation coefficient of 0.95 and RMSE of 3.1?).(2)The MYJ+BEP configuration simulated 2 m specific humidity best,as indicated by its correlation coefficient(0.85)and RMSE(0.57 g/kg);at night,the MYJ+UCM configuration simulated the specific humidity profile best(with a correlation coefficient of 0.93 and RMSE of 1.75 g/kg).During the day,the BL+BEP configuration performed best(with a correlation coefficient of 0.97 and RMSE of 0.5 g/kg).(3)The MYJ+BEP configuration simulated the 10 m wind speed best(with a correlation coefficient of 0.91 and RMSE of 1.26 m/s);the BL+BEM configuration simulated the wind profile best both at night(with a correlation coefficient of 0.99 and RMSE of 0.77 m/s)and during the day(with a correlation coefficient of 0.98 and RMSE 2.46).(4)The BL+BEM configuration simulated the 10 m wind direction best(with an RMSE of 25.91°);the BL+BEM configuration simulated the vertical profile of wind direction best during the day(with an RSME of 5.35°);and the BL+UCM configuration performed best at night(with an RMSE of 11.97°).(5)The BL+BEM configuration simulated the basic characteristics of the vertical profiles of meteorological parameters best over plain area in summer clear days.Based on the BL+BEM scheme,the diurnal variations and vertical structure of heat islands in Beijing was studied.The results show that:(1)The strongest UHI(Urban Heat Island)intensity near surface appears at night,which can reach 7.16?.The UHI intensity will continue being positive until the sunrise.After sunrise,UHI intensity decreases smoothly,and the weakest appears before noon,which is-0.26?.The UHI intensity return to positive after noon,but is weaker than it was at night.After sunset,the UHI intensity increase rapidly,and strong urban hear island is exist during 18:00?06:00.(2)The development of turbulence is relatively weak both in the suburbs and in the urban areas at night,which is not conducive to the vertical development of the heat island.At 14:00,the existence of buildings over the urban area makes the turbulent energy larger,which can reach the maximum.4m2/s2,but the suburbs can only reach 0.5 m2/s2,so that the heat island range can be maintained at a high altitude.(3)Under the influence of the inversion layer at night,the intensity of the maximum urban heat island can reach 5.5?,which can only be maintained below 200m because of the impact of the boundary layer jet;at noon,the intensity of the urban heat island is only about 2 ?.The height of the mixed layer reaches 2500m,and the turbulent flow fully develops,thus the height of the heat island can also be extended to 900-1800m.The heat island intensity,relative humidity difference,and wind speed difference remain the same with the height,but the influence area of heat island and dry island range decrease with the height.Boundary layer jets over urban area will inhibit the vertical development of urban heat islands,while boundary layer jets over suburban area will promote the vertical development of urban heat islands.WRF model with the incorporation of a Single Layer Urban Canopy Model is used to investigate the cooling effect of the roof greening in Nanjing.Sensitivity tests of albedo,heat capacity,thermal conductivity and humidity are conducted for the time period from July 28 to July 29.The simulation results show that(1)the albedo of the roof is reduced to approximately 0.15 after greening,which is smaller than the albedo values of the roofs consist of cement or other reflective materials.This decrease of the albedo increases the city temperature by 0.2? in daytime.(2)The heat capacity of the roof increases significantly after greening,leading to the mitigation of the temperature by 0.33 ? during daytime.In contrast,the temperature at night increases by about 0.21?.(3)Due to the existence of the vegetation and the soil layer,the thermal conductivity of the roof is weakened.As a result,the net radiation on the roof is more easily converted to sensible heat rather than being transferred downwards,which warms the overlying ambient air.(4)The change of the soil humidity enhances the release of the latent heat from the net radiation on the roof.Therefore,the temperature in daytime and nighttime is reduced by about 1.23? and 0.44?,respectively.(5)The statistical analysis of the simulation results for different seasons shows that the reduction of temperature by roof greening is the strongest during the summertime,which amounts to 1.22? on average.In comparison,the temperature decreases by about 0.96? in spring,0.75 ? in autumn and only 0.38 ? in winter.