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

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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.