The Study for Spatial Structures and Time Development of Turbulence in the Atmospheric Boundary Layer

本文通过观测和数值试验研究了中性稳定度条件下湍流的空间结构和时间发展。首先，分析了柴崎市风场效应实验室和茂崎县观测站的观测资料。为了得到大风区域的平均模式，对测得的20m高空平均风向的风向分量进行了160秒连续小波变换。利用俄克拉荷马大学风暴分析预报中心开发的ARPS(高级区域预报系统)对大涡进行了数值模拟。在初始条件下，水平均匀场的风廓线在30m以下为对数线性风律，上方为Ekman螺线，位温廓线为近中性，最上层为逆温层，在该场上产生了随机位温扰动。积分时间为35040秒后，沿平均风向拉长的条纹状结构在近地表突出。7.5m高度的平均风向分量的小波方差在720m的空间尺度上最大。小波方差峰值附近的平均模式显示了从约150米的高度向下移动的高速区。平均风向为600米、垂直方向为240米的区域动量通量大于300米高度以下的其他区域。

In this study, the spatial structures and time development of turbulence was investigated using observations and numerical experiments for the neutral stability condition.At first, observed data at Shionomisaki Wind Effect Laboratory and Shigaraki MU Observatory was analyzed. To make an averaged pattern for the area of strong wind, continuous wavelet transform in the time scale of 160 seconds was applied to the wind component in mean wind direction measured at a height of 20 meters. The structures of the downward moving high-speed area and upward moving low-speed area ahead of it are shown.To execute numerical experiments, the ARPS (Advanced Regional Prediction System) developed by the CAPS (Center for Analysis and Prediction of Storms) at the University of Oklahoma was used for the large eddy simulation. For the initial condition, random potential temperature perturbation was induced on the horizontally homogeneous filed which has a wind profile with the log-linear wind law below the 30 meters and the Ekman spiral above it and an almost neutral potential temperature profile with uppermost inversion layer. After the integration time of 35040 sec., streaky structures elongated in mean wind direction are outstanding near the surface. Wavelet variance for the wind component in mean wind direction at a height of 7.5 meters is maximum at the spatial scale of 720 meters. Averaged pattern around the peak position for the wavelet variance shows the downward moving high-speed area from the height of about 150 meters. The area in length of 600 meters in mean wind direction and 240 meters in normal direction shows larger momentum flux than other areas below the height af 300 meters.