Mass and energy exchanges in the urban canopy directly affect urban atmospheric thermodynamic and dynamic processes,and thus affect the structure of the urban boundary layer.Urban canopy parameterization is an indispensable physical process in the numerical simulation of atmospheric motion.In the present work,simulations were conducted for the urban thermal environment of Nanjing under typical summer weather conditions (sunny days with weak wind),for the period 1-3 August 2010,using the WRF model.By selecting a parameterization that considered the urban canopy structure (UCM experiment),and one that did not (NOUCM experiment),the boundary layer characteristics over different underlying surfaces were examined.The results showed that: (1) The UCM simulation results agreed with the observational data very well.The simulation of 2-m temperature was improved considerably compared to that of NOUCM.Moreover,the drag of buildings to near ground wind speed was better reflected;the simulation of 10-m wind speed was substantially improved.According to observational data analyses,the heat island intensity reached its maximum at 2100 BST,and was about 4 ℃.The UCM scheme simulated a value of around 3 ℃,while the NOUCM scheme simulation yielded a value of around 1.5 ℃. (2) The UCM experiment simulated the 3D heat island distribution favorably.Owing to the retention of radiation,the heat island at 1400 BST was relatively strong,and it covered a wide range at about 2 m above the ground (~120 km²),with an intensity of 2 ℃.The heat island intensity in the NOUCM scheme simulation was 1 ℃.Meanwhile,due to the existence of urban structures,the turbulent kinetic energy was greater and the upward vertical diffusion increased.At 20 m above the ground,an obvious heat island effect could still be found,and the intensity produced using the UCM scheme was 1.5 ℃.The heat island range in the NOUCM experiment was substantially narrower,and the intensity was 0.8 ℃.At around 55 m above the ground,the heat island range simulated using UCM narrowed,and the intensity was 1.1 ℃;meanwhile,the intensity of the NOUCM scheme was only 0.4 ℃.Based on the UCM simulation,the ground heat diffusion effect during the day reached 143 m,the heat island at 02:00 BST and 2 m above the ground reached a maximum of 2 ℃,and there was a detectable heat island impact above 70 m.Based on the NOUCM simulation,however,the range of the simulated heat island shrank rapidly with height,and a heat island effect could not be found with an obvious inversion phenomenon. (3) Different underlying surfaces produce distinct boundary layer features,with cities having distinct impacts on surrounding underlying boundary structures.During the day,turbulent mixing was enhanced at 14:00 BST in urban areas,and the urban boundary layer height increased to about 100 m.At night,the stable inversion stratification of the suburbs cropped the underlying surface,and the Purple Mountain vegetation underlying surface decreased significantly at 02:00 BST because of the presence of the urban canopy structure.For water,near-surface potential temperature and air temperature were mainly affected by the water.Cities have a limited impact on near-surface water;however,they appear to gradually influence surface water after a certain height.