太湖风生流垂向切变规律的原位观测

浅水湖泊垂向环流存在着上下层反向现象,为了探究太湖湖流垂向切变规律,用声学高频流速仪ADV、ADP及风向风速仪在梅梁湾进行了9 d的连续观测;基于获取的高频同步数据,利用概率统计方法,对各层流场在不同风向、不同风速以及持续同向风场影响下的切变率进行了统计分析,并研究了流场垂向分布特征。结果表明:5月太湖梅梁湾在风向为ESE、ES、E,风速2~5 m/s,同向风场持续作用10~11h时,流场基本达到稳定且切变率最大;表层流场(水下50cm)处,切变率最小,为20%,底层流场(距水-土界面7 cm)处,切变率最大达到60%;流向改变的拐点出现在表层至中层,即水下50~100 cm;风速、风向的出现频率,以及同向风场的持续时间决定了流场反向率大小,流场反向率决定了拐点的位置。

Field observation of vertical shear of wind-driven current in Taihu Lake

Reverse vertical circulations often exist in shallow lakes. In order to investigate the shear rules of the vertical circulation in Taihu Lake, field observations were conducted in Meiliang Bay for nine days using an acoustic Doppler velocimeter(ADV), an acoustic Doppler current profiler(ADP), and anemometers. The shear probabilities at different water depths, which were affected by different wind directions, wind speeds, and continued wind fields with the same direction, were analyzed based on the statistics of synchronous and high-frequency data of wind-driven currents. The characteristics of the vertical profile distribution of the flow field were also studied. The results show that, when the wind moved in the ESE, ES, and E directions at a speed ranging from 2 to 5 m/s and the wind fields moving in the same direction were active for 10 to 11 hours in Meiliang Bay in May, the flow field could be stable with the highest shear rate. The shear rate was lowest with the value of 20% in the surface layer(50 cm below the water surface), and highest when it had a value of 60% in the bottom layer(7 cm above the lakebed). The inflection point, where the flow direction changed, appeared between the surface layer and middle layer, i. e. , 50 to 100 cm below the water surface. The occurrence frequencies of wind speed and wind direction, as well as the duration of wind fields with the same direction determined the reverse probability of the flow field, which determined the location of the inflection point.