乌日柴胡,王建捷. 2019. 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, (0):-, doi:10.11676/qxxb2019.059
北京山区与平原冬季近地面风的精细观测特征
Observational investigation on fine features of the near surface wind in winter over Beijing area
投稿时间:2019-02-21  修订日期:2019-05-18
DOI:10.11676/qxxb2019.059
中文关键词:  北京复杂地形,近地面风,观测特征
英文关键词:Complex topography of Beijing, Near-surface wind, Observational characteristics
基金项目:国家重点基础研究发展计划
作者单位E-mail
乌日柴胡 中国气象科学研究院 wurichaihu88@163.com 
王建捷 国家气象中心 wangjj@cma.gov.cn 
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中文摘要:
      [资料和方法]本文利用2009-2018年冬季北京地区两百多个自动站逐时10m风观测数据,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精细特征,并使用有完整记录的两年(2017年和2018年)冬季延庆高山区不同海拔高度10m风逐时观测数据,多视角分析探讨高山区不同海拔高度近地面风特征和成因,[目的]以深刻认识北京地区复杂地形条件下冬季近地面风的观测特征和独特规律,并揭示其中高山山地近地面风的未知特征。[结果和结论]结果表明:(1)北京地区冬季近地面平均风呈现出受西部北部地形、城市下垫面粗糙度和冷空气活动共同影响的特征,即: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弱;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)四个典型区域冬季近地面风速日变化都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,这一特征在城区的稳定性高于其它区域、山区相对最低。(3)四个区域冬季弱风(<1m/s)频率可达31%-42%,城区最高、山区最低;强风(>10.8m/s)频次则是山区最多、城区甚少,强风主要表现为偏西-偏北风、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。(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1500m附近(平均的边界层顶高度)是延庆高山梯度近地面风速日变化特征的“分水岭”,位于此海拔高度内的站风速日变化表现为前述 “峰强谷平”单峰特征,而此海拔高度以上站风速日变化则呈现出相反特点——夜间大白天小、午间最小的“峰平谷深”特点,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加,高海拔站点日平均风速几倍于低海拔站点值。白天-前半夜时段,两个高海拔站冬季盛行偏西风、风向变化不大,但风速可在2-12m/s区间中变化;两个低海拔站则风速比较稳定(<6m/s),但风向从午间到傍晚相对多变。
英文摘要:
      Abstract In this paper, the fine features of the near surface wind in winter over 4 typical areas of Beijing (the mountain area, the transition area between mountain and plain, the plain area, and the urban area), as well as the alpine area of Yanqing, were investigated based on two sets of hourly observed 10m wind data from conventional Automatic Weather Stations (AWS) network over Beijing area and special AWS observations in Yanqing alpine area. Results show that: 1) In winter, the average near-surface wind characteristics over Beijing area are reflective of the effects of the west and north topography of Beijing, the roughness of its urban underlying surface and cold-air injection, such as, wind speed is distributed along the topographic gradient with higher speed in western/northwestern mountain area, lower in the plain area, and the lowest 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 transition areas. 2) In four typical areas, there is a similar diurnal variation feature on wind speed: higher wind speed in the daytime than that in the nighttime, and the highest single-peak around noon time. Comparing to other 3 areas, the above feature is most stable in urban area suggested by the low data variance. 3) Weak wind (<1m/s) frequencies in the four typical areas are among 31%-42%, with the highest frequency in urban area and lowest frequency in mountain area. Strong wind (>10.8m/s) mostly coming from the west to north directions and closely linked to cold-air injection, shows the opposite pattern. Southerly wind is the least frequent in urban, plain and transition 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 above mentioned typical diurnal variation feature, while the two AWSs above that altitude shows the opposite characters. This is related to the diurnal variation of turbulence in the PBL and the downward momentum transmission from the lower free atmosphere to the PBL. 5) The average daily wind speed of two higher-altitude stations in the Yanqing alpine area is several times larger than that of two lower-altitude stations. During the daytime to midnight, westerly winds prevail at the two higher-altitude stations, while wind speed could vary from a wide range. On the contrary, for the two lower-altitude stations, wind speed is relatively stable, but directional change is more frequent.
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