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

在中性稳定条件下，通过观测和数值实验研究了湍流的空间结构和时间发展。首先，对盐咸风效应实验室和新垣MU天文台的观测资料进行了分析。为了得到强风区域的平均格局，对20米高度测得的平均风向的风分量进行160秒时间尺度的连续小波变换。给出了高速下移区和低速上移区的结构。为了进行数值实验，使用俄克拉荷马大学风暴分析与预测中心开发的ARPS（高级区域预测系统）进行大涡模拟。初始条件下，在30 m以下为对数线性风律风廓线，30 m以上为Ekman螺旋风廓线，30 m以下为近中性位温廓线，上有逆温层的水平均匀场上产生随机位温扰动。在35040秒的积分时间后，地表附近的条纹状结构在平均风向上呈现出明显的拉长。在720米空间尺度上，7.5米高度平均风向风分量的小波方差最大。小波方差在峰值位置附近的平均模式显示了从约150米高度开始向下移动的高速区域。平均风向长度为600米、法向长度为240米的区域，其动量通量大于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.