This study investigates interactive effects from the Beijing urban area on temperature, humidity, wind speed and direction, and precipitation by use of hourly automatic weather station data from June to August 2008-12. Results show the Beijing summer urban heat island (UHI) as a multicenter distribution (corresponding to underlying land-use features), with stronger nighttime than daytime values (averages of 1.7 degrees vs 0.8 degrees C, respectively). Specific humidity was lower in urban Beijing than in surrounding nonurban areas, and this urban dry island is stronger during day than night (maximum of -2.4 vs -1.9 g kg(-1)). Wind direction is affected by both a mountain-valley-breeze circulation and by urbanization. Morning low-level flows converged into the strong UHI, but afternoon and evening southerly winds were bifurcated by an urban building-barrier-induced divergence. Summer thunderstorms also thus bifurcated and bypassed the urban center because of the building-barrier effect during both daytime and nighttime weak-UHI (<1.25 degrees C) periods. This produced a regional-normalized rainfall (NR) minimum in the urban center and directly downwind of the urban area (of up to -35%), with maximum values along its downwind lateral edges (of >15%). Strong UHIs (>1.25 degrees C), however, induced or enhanced thunderstorm formation (again day and night), which produced an NR maximum in the most urbanized area of up to 75%.
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机译：本研究使用2008年6月至2008年8月的每小时自动气象站数据，调查了北京市区对温度，湿度，风速和风向以及降水的互动影响。结果显示，北京夏季城市热岛（UHI）是一个多中心分布（对应于潜在的土地利用特征），夜间的昼夜强度大于白天的昼夜强度（平均值分别为1.7度和0.8摄氏度）。北京市区的比湿度比周围的非城市地区要低，而且这个城市的干燥岛白天比夜晚强（最大-2.4对-1.9 g kg（-1））。风向既受山谷微风的流通又受城市化的影响。早晨的低水平气流汇聚成强劲的UHI，但午后和傍晚的南风由于城市建筑障碍引起的发散而分叉。由于白天和夜间的弱UHI（<1.25摄氏度）期间的建筑屏障效应，夏季雷暴也因此分叉并绕过市中心。这在市区中心和市区的顺风处产生的区域归一化降雨（NR）最小值（最高-35％），在顺风侧向边缘的最大值（> 15％）。然而，强UHI（> 1.25摄氏度）诱导或增强了雷暴形成（白天和黑夜），这在最城市化的地区产生的NR最大值高达75％。
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