Numerical Simulation Study Of Underlying Surface Obstacles Effect On Observation Environment

Observation environment have important influence on accurate observation of meteorological elements. Special underlying surface like water body and building are important observation environment that have influence on meteorological elements observation. This paper firstly studied the impact of Qingshan Lake(6.5km2), which is in Zhejiang Province, on surrounding air temperature at the height of2m by using WRF model, in the clear sky conditions and overcast conditions of four seasons respectively. The results showed that:(1) The average RMSD of temperature at2m was2℃, calculated by comparing the2m air temperature obtained from the model with those obtained from the10observation stations in the fourth nestification of the model, and the average correlation coefficient was0.85, both of the values indicated that WRF model could reflect the variation of2m air temperature.(2) The effect of water body on surrounding air temperature may remarkably vary with the season and weather change. It could increase surrounding air temperature in winter and autumn due to the stable weather condition, and could decrease in spring. The temperature of water body was lower compared with surrounding air temperature in summer, the influence wasn’t so obvious because of the complex local thermodynamic circulation.(3) The distance of water body effect greatened with the increasing of water body area. As the mechanism analysis of the water body effect on surrounding air temperature, the effect occurred through advection, but when the wind speed is higher than6.2m/s, the thermodynamic property divergence between water and land could be quickly carried away by advection, so the effect was not obvious. And turbulent diffusion could transmit the thermodynamic property divergence upward, the effect became not so obvious when the turbulence intensity was larger than0.5m2/s2.(4) Lake had less impact on the humidity around it in spring and summer, but in autumn and winter, the impact was obvious which could be7g/kg. The existence of the lake increased the wind speeds around it except spring. The turbulent kinetic energy (TKE) above the lake was small during the day all the year around, the turbulent exchange above lake was weak in spring and summer, reduced the height of the boundary layer. In the winter, the situation was just the opposite at night, TKE was high and boundary layer height could reach to400m.(5) The effect of Qingshan lake on observed leeward air temperature, humidity, wind speed could reach to3.5km、2.7km、6.5km respectively. Then the City Sub-domain Scale Model (CSSM) developed by Nanjing University was used to study the effect of a single building on surrounding meteorological environment in ideal condition. The results showed that:(1) Under neutral stratification condition, the6-meter-high building had no obvious effect on surrounding air temperature. When building is12m, it had obvious influence to surrounding air temperature, the maximum impact distance could reach260m. The effect of building on surrounding air temperature increased with a higher speed of wind when wind is stronger than6m/s. The effect of building on surrounding air temperature was also related to the height of building. The cooling effect caused by building bridging effect was stronger with a higher building, thus surrounding temperature increased less, the influence distance was shorter.(2) Under convection condition, when building is12m, it had obvious influence to surrounding air temperature, the influence distance could be110m, much less than that under neutral stratification, because the unstable stratification transport heat upward. There’s no big difference of influence distance between12-meter-high and18-meter-high building.(3) Under stable stratification condition, the6-meter-high building had effect on surrounding air temperature, the influence distance could be100m when the wind speed is10m/s.The effect of shielding had a larger effect on air temperature, there’s no regular pattern of influence distance varying with building height and wind speed.