| 北京山区与平原冬季近地面风的精细观测特征 |
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| 引用本文： | 乌日柴胡,王建捷,孙靖,黄丽萍,孙健.北京山区与平原冬季近地面风的精细观测特征[J].气象学报,2019,77(6):1107-1123. |
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| 作者姓名： | 乌日柴胡 王建捷 孙靖 黄丽萍 孙健 |
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| 作者单位： | 1.中国气象科学研究院, 北京, 100081 |
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| 基金项目： | 国家重点研发计划重点专项项目（2017YFC1502001）。 |
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| 摘 要： | 利用2009—2018年冬季北京地区200多个自动气象站逐时10 m风速、风向观测数据，分典型区域（山区、山区与平原过渡区、平原区、城区）研究北京地区冬季近地面风的精细特征，并使用有完整记录的2 a（2017和2018年）冬季延庆高山区不同海拔高度10 m风逐时观测数据，多视角分析高山区不同海拔高度近地面风的特征和成因，以深刻认识北京地区复杂地形条件下冬季近地面风的特征和规律。结果表明:（1）北京地区冬季近地面平均风受西部北部地形、城市下垫面粗糙度和冷空气活动共同影响，平均风速沿地形梯度分布，山区高平原低，平原中又以城区风速最小；盛行西北风和北风，在城区东、西两侧盛行风出现扰流，在山区和过渡区一些地方还存在与局地地形环境明显关联的其他盛行风向。（2）4个典型区域冬季近地面风速日变化均表现为白天风速大于夜间，午间风速最大的“峰强谷平”单峰特征，这一特征的稳定性在城区高、山区低。（3）4个区域冬季弱风（< 1 m/s）频率为31%—42%，城区较高、山区较低；强风（> 10.8 m/s）频次则是山区多、城区少，强风风向主要表现为偏西—偏北，与冷空气活动密切关联；城区、平原区和过渡区偏南风频率均为极小，暗示北京“山区—平原”风模态在冬季是“隐式”的、不易被直接观测到。（4）近地面风的水平尺度代表范围在延庆高山区高海拔处明显大于低海拔处，海拔1500 m附近（平均的边界层顶高度）是延庆高山近地面风速日变化特征的“分水岭”，低于该海拔高度时近地面风速日变化表现为前述“峰强谷平”单峰特征，而高于该海拔高度时近地面风速日变化则呈现相反特征，即夜间大白天小、午间最小的“峰平谷深”特征，这是由边界层湍流活动的日变化及伴随的低层自由大气动量向边界层内下传所致。（5）延庆高山近地面风速大体上随观测高度而增大，高海拔站点日平均风速数倍于低海拔站点。白天—前半夜，海拔约2000 m的站点冬季盛行偏西风，风向变化不大，但风速为2—12 m/s；1000 m左右的低海拔站则风速比较稳定（< 6 m/s），风向从午间至傍晚相对多变。
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| 关 键 词： | 北京复杂地形 近地面风 观测特征 |
| 收稿时间： | 2019/2/27 0:00:00 |
| 修稿时间： | 2019/6/17 0:00:00 |
An observational investigation of fine features of near surface winds in winter over Beijing area |
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| WU Richaihu,WANG Jianjie,SUN Jing,HUANG Liping and SUN Jian.An observational investigation of fine features of near surface winds in winter over Beijing area[J].Acta Meteorologica Sinica,2019,77(6):1107-1123. |
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| Authors: | WU Richaihu WANG Jianjie SUN Jing HUANG Liping and SUN Jian |
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| Institution: | 1.Chinese Academy of Meteorological Sciences, Beijing 100081, China2.National Meteorological Center, Beijing 100081, China3.Numerical Weather Prediction Center of China Meteorological Administration, Beijing 100081, China |
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| Abstract: | The fine features of near surface winds in winter over four typical areas of Beijing (the mountain area, the transitional area between mountain and plain, the plain area, and the urban area), as well as the alpine area of Yanqing, are investigated based on two sets of hourly observations of 10 m wind collected at conventional Automatic Weather Stations (AWS) network over Beijing area and special AWS observations in Yanqing alpine area. Results are as follows:(1) In the winter, the average near-surface wind characteristics over Beijing area reflect the joint effects of the topography in western and northern Beijing, the roughness of its urban underlying surface and cold-air injection. The wind speed is distributed along the topographic gradient with higher speed in western/northwestern mountain area, lower speed in the plain area, and the lowest speed in the urban area; prevailing winds in the northwest and north directions (relevant to cold air) bypass the urban area, and local dominant wind directions (non-northwest and north directions) exist in some mountain and transitional areas. (2) In the four typical areas, the wind speed exhibits similar diurnal variation feature, i.e., the wind speed is higher in the daytime than in the nighttime, and the highest single-peak occurs around noon time. Compared to the other three areas, the above feature is most stable in urban area suggested by the low data variance. (3) Weak wind (< 1 m/s) frequencies in the four typical areas are between 31%-42%, with the highest frequency in urban area and the lowest frequency in mountain area. Strong wind (> 10.8 m/s) that mostly comes from the west to north directions and is closely linked to cold-air injection shows an opposite pattern. Southerly wind is the least frequent in urban, plain and transitional areas, indicating that the well-known regional mountain-plain wind system of Beijing exists implicitly and is hardly detectable in winter. (4) The altitude around 1500 m (the general top of the Planetary Boundary Layer (PBL)) is the turning point of the diurnal variation feature of near surface wind speed at Yanqing alpine area. Two AWSs below that altitude reflect the typical diurnal variation feature mentioned above, while the two AWSs above that altitude show the opposite characters. This is related to the diurnal variation of turbulence in the PBL and the downward momentum transfer from the lower free atmosphere to the PBL. (5) The average daily wind speed at the two higher-altitude (about 2000 m) stations in the Yanqing alpine area is several times larger than that at the two lower-altitude (about 1000 m) stations. From the daytime to midnight, westerly winds prevail at the two higher-altitude stations, while wind speed could vary within a wide range. On the contrary, for the two lower-altitude stations, the wind speed is relatively stable, but directional change is more frequent. |
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| Keywords: | Complex topography of Beijing Near-surface wind Observational characteristics |
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