基于风廓线仪的华南地区夏季边界层湍流统计特征研究

TURBULENT STRUCTURE OF THE BOUNDARY LAYER IN SUMMER OVER SOUTH CHINA AS REVEALED BY WIND PROFILER

采用双权重算法,使用2015年6—8月我国东南部业务风廓线雷达资料,通过湍流脉动垂直速度方差和偏度的计算和分析,对晴空和低云主导情况下的边界层湍流特征以及中小尺度局地环流对于边界层湍流的影响进行研究。主要结论如下:(1)晴天情况下垂直速度标准差和垂直速度偏度都具有明显的日变化特征,湍流主要由下垫面加热驱动发展;(2)在低云主导情况下,湍流明显弱于晴天对流边界层的湍流强度,边界层内湍流的发展不仅受地面加热的影响,而且在边界层上部存在明显的自上而下发展的湍流,这主要是由于边界层顶云辐射冷却造成的;(3)除了上述两种情况,边界层湍流发展同时受到局地中小尺度环流或者天气系统的影响,因而呈现出更多的复杂性。

Using a bi-weighting quality control algorithm,three-month(June,July and August)operational wind-profile radar(WPR)data are collected to calculate the vertical velocity standard deviation and skewness in the planetary boundary layer(PBL).The combination of these two statistics is used to investigate the characteristics of the turbulence in PBL under sunny and low-cloud covered conditions,as well as the turbulent structure influenced by local small-scale circulation.The main conclusions are as follows.(1)The operational WPR data clearly discloses significant diurnal variations of the vertical velocity standard deviation and skewness in sunny days,indicating that the typical convective PBL turbulence occurrence is mainly due to surface heating.2)When low clouds are present around the PBL top,the turbulence intensity is weaker than that in the convective boundary layer(CBL).Usually,there exist two intensive zones of turbulence in the PBL,one is similar to the CBL case which is driven by the surface heating,and another is found to occur from the top of PBL mainly due to the effect of cloud radiative cooling,showing a top-down mechanism.(3)Besides the typical sunny and cloudy cases,about 66.4%of the cases in the three months show much complex turbulence structures,which is influenced by local small-scale circulations or large-scale weather systems.