Coplanar scans from three Doppler lidars are used to retrieve the horizontal wind field in a horizontal plane of about 5 km × 5 km in size above the city of Stuttgart in south-western Germany. Stuttgart is located in moderate mountainous terrain that is characterized by a basin-shaped valley (Stuttgart basin) which opens into the larger Neckar Valley. Using the retrieved horizontal wind field, which is available on 22 days with a temporal resolution of 1 min and a horizontal resolution of 100 m, we investigate the mesoscale structure of the horizontal flow in the valleys with respect to time of the day, stratification and wind above the mean ridge height, and determine how fast the cells in the convective boundary layer move downstream, i.e. we estimate the convection velocity. The measurements reveal a large spatial and temporal variability of the flow. During stable conditions, the flow below the mean ridge height is decoupled from the flow aloft and downvalley wind dominates in the valleys. At the opening of the Stuttgart basin into the Neckar Valley outflow dominates during nighttime, whereas inflow into the basin prevails in the early morning. During thermally unstable conditions the flow in the valleys is mainly coupled to the flow aloft with a preference for upvalley wind direction. Convective cells moving downstream are detected in the horizontal wind field and a method to estimate the convection velocity from the horizontal wind field measurements is presented. The mean convection velocity is found to be higher by 24 % than the mean horizontal wind speed at the same height and about similar to the wind speed 100 m further up.

中文翻译：

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使用共面多普勒激光雷达扫描检测复杂地形上水平风场中的结构

来自三台多普勒激光雷达的共面扫描用于检索德国西南部斯图加特市上方约 5 公里 × 5 公里大小的水平面中的水平风场。斯图加特位于中等山地地带，其特点是盆地状山谷（斯图加特盆地）通向较大的内卡河谷。使用检索到的 22 天的水平风场，时间分辨率为 1 min，水平分辨率为 100 m，我们研究了山谷中水平流的中尺度结构，包括时间、分层和风高于平均脊高度，并确定对流边界层中的细胞向下游移动的速度，即我们估计对流速度。测量结果揭示了流动的大空间和时间可变性。在稳定条件下，低于平均山脊高度的气流与高处的气流分离，谷底风在山谷中占主导地位。在斯图加特盆地进入内卡河谷的开口处，夜间流出量占主导地位，而流入盆地的流入量则在清晨盛行。在热不稳定条件下，山谷中的气流主要与高处的气流耦合，并优先考虑上谷的风向。在水平风场中检测到向下游移动的对流单元，并提出了一种根据水平风场测量值估计对流速度的方法。