The Study Of The Impact Of Surrounding Water Body And Building On Temperature And Wind Observation

To evaluate the effect of waters and obstacles on atmospheric temperature and wind observation quantitatively, this paper studied the impact range of different-scale waters and obstacles on temperature and winds through numerical simulation and observational experiment. In addition, sensitivity experiments analysis was performed as well.1. Two observing experiments were carried out in Qianmudang and Hangzhouwan, which indicate that the air temperature around the water body increases at night and decreases at daytime in winter and spring. The nearer to the water body, the more obvious the temperature is affected. For small-scale water body, the affected scope reaches 200 m in winter while for large-scale water body, the scope extends to about lkm, but in spring the affected scope gets clearly smaller. There are wind speed thresholds for the impact at night,3 m/s for smaller water body,4 m/s for larger one. When wind flow is slower than the threshold, the warming effect is obvious. However, if the wind speed is beyond the threshold the effect is not noticeable. The cooling effect at daytime is not influenced by wind speed so much.2.To evaluate the requirements for the distance of the water body from the air temperature, the numerical simulation, sensitivity experiment and mechanism analysis on water body were conducted. The results indicate that the simulation values are in a reasonable distribution, the simulated and observed values are close to each other, sharing similar varying trends, so the WRF model is proved to have the ability to simulate the water body. Moreover, the simulations shows waters in different scales all create the effect on temperature that is warming at night but cooling at daytime. The affected scopes are smaller than the observations. The 0.5 ℃ warm curve is 100 m for small water body, and the 0.2 ℃ warm curve is 3.7 km for large water body. The effect of water body on leeward wind is mainly via advection transport effects. Sensitive analysis on background wind speed, initial temperature and weather condition shows that when the wind speed is limited to the threshold at night, the faster the wind blows, the bigger influence the water body has on leeward wind, but if wind speed is larger than or equal to the threshold, the influence of water body does not change with wind speed. The initial wind speed has more obvious effect on water body at night than at daytime. The warmer temperature at night means the water body has smaller affected ranges, but the situation is opposite at daytime. Therefore, varying weather conditions contribute significantly to different effects of water body on temperature.3. To evaluate how obstacles impact wind field, observing experiment was carried out in Guyuan. The experiment results indicate that when the obstacle is higher than 6 m, it can weaken the wind speed obviously. The faster the background winds blow, the stronger effect the obstacle has on the wind speed. When the angle between the wind direction and obstacle is 90 ℃, the average attenuation ratio of wind speeds is 43.6%,24.8% and 22.7%, respectively corresponding to the distances of 6,8 and 10 times the obstacle height when it is 15 m high:the average attenuation ratio of wind speed is 49.2%,35.4% and 23.8% corresponding respectively to the distances of 6,8 and 10 times the obstacle height when it is 12 m high; and the average attenuation ratio of wind speed is 52.3%,38.4% and 28.7 % corresponding to the distances of 6,8 and 10 times the obstacle height when it is 9 m high. When the angle between the wind direction and obstacle is 45 ℃, the wind speed attenuation ratio of the 12.5℃ direction is bigger than that of the 45 ℃ direction. The influence distance of obstacles on wind speed is about 6 times the obstacle height vertically, and 8 times of the obstacle height at the 45 ℃ wind direction. But when the obstacle is shorter than 6 m, its influence on wind speed is less obvious.4. To evaluate the requirements for the distance of the obstacles from the anemometer, a set of numerical simulations on an isolated building by CFD model were carried out. The results indicate that the simulation values a basically reasonable distribution, the simulated and observed values are closer to each other and their changing trends are consistent, so the CFD model has the ability to simulate the airflows surrounding obstacles. The range of 90% inflow speed is 25, 25.2 and 33 times the obstacle heights in leeward side when the heights of the obstacles are 15 m,12 m and 9 m accordingly. With the decreasing height of obstacles, the requirement to the spacing height ratio increases. The influence distance of wind direction is 6-7 times the height of the obstacle in the leeward side, but when the obstacle is less than 6 m, its effect on winds is not remarkable.