| 摘要: | 淺海地區的洋流受風的作用變化很大，但過去礙於觀測儀器解析度的限制，缺乏高解析度的海流垂直資料，難以詳細描述海流對於遭受強風下在垂直分層上的反應。本研究利用垂直高解析度的ADCP海流資料(2001/5/22?2001/6/26)，探討烏坵海域海流特性，包括潮流、亞潮流、亞潮流受風的影響及在強風作用下表層艾克曼層的生成和底部艾克曼層的特性，以及底部邊界層內黏滯係數的變化。 由觀測資料得知，潮流橢圓半長軸方向都和等深線一致，潮流受密度分層影響很大，使垂直潮流明顯分為兩層。而亞潮流受風影響的深度，大概為上層10 m，同樣亞潮流也受密度分層影響大，使受風影響的層面無法發展下去。在資料後半段，恰好奇比颱風經過；在奇比侵襲前，颱風前，表面和底部艾克曼層都不清楚；而在颱風最接近測站時，流場為表面和底部艾克曼層都清楚顯示，而表面艾克曼層受密度分層影響無法發展到底部，流場結構都是分成兩層水層；在颱風後，底部流場有順時針流產生，而之後26日流場底部和表面艾克曼層皆變為不明顯。 由海流累積向量圖發現海流在受風的影響下，發展成表層艾克曼層，底層海流則因為受摩擦力影響，在距儀器17 m的深度，發展成底部艾克曼層。並利用Zikanov et al. (2003)推測的黏滯係數公式，代入實測資料，且假設在底部邊界層摩擦係數隨著深度變化ν(z)，帶回原來的動量平衡方程式，簡單推估黏滯係數的變化，迴歸出在此處的 ，迴歸曲線為一個指數變化的曲線，底部邊界層的黏滯係數隨著離底距離越大而增加，但不包含距邊界層3 m以下。和Zikanov et al. (2003)距儀器1-17 m的黏滯係數變化大致相似，只有在底部不相同，Zikanov的曲線在距儀器5 m以下，黏滯係數變為增加，本研究資料分析結果則是持續變小至距儀器3 m的趨勢。 The neritic area ocean current changes very big by the wind, but limited by the past instrument resolution and lacked the fine resolution of the ocean current vertical data that would be difficulty to described the vertical stratification ocean current response to suffer a strong stiff wind. This research use vertical fine resolution ADCP ocean current data (2001/5/22~2001/6/26), discusses the Wuchiu sea area ocean current characteristic, including the tidal current, the sub-tidal current, the sub-tidal current influence by the wind and under the wind produces the surface Ekman layer and the Ekman layer at the bottom of the ocean characteristic, as well as the change of the viscosity in the boundary layer. According to the observed data, the semi-major axis direction of the tidal current ellipse is consistent with the isobaths.The density stratification have huge influence in the tidal current , and leads the vertical tidal current to divide into obviously two layers. But the sub-tidal current influenced depths by the wind probably for upper formation 10 m, similarly sub-tidal current also affected by the density stratification in a big way, such as to the influenced layer to be unable developing. In the end of the data, it happened to a typhoon process. Before the typhoon processing , the surface and the bottom of Ekman layer are not all clear; but when the typhoon closest the station, the flow field all clearly appeared the surface and the bottom Ekman layers, but the surface Ekman layer is unable to develop the bottom, because of the density stratification influence , the flow field structure is divides into two layers; After the typhoon, the bottom flow field rotates clockwise, but on 26th the bottom and the surface Ekman layer becomes not obviously. By the ocean current accumulated vector diagram discovered the ocean current develops the surface layer Ekman layer, because of the friction force influence, the bottom current developing the bottom Ekman layer from instrument 17 m apart. Utilizing the effective viscosity formula of depth Zikanov et al. (2003) ,substitute actual data, assumed the bottom boundary layer viscosity along with depth change ν(z), substitute back to the original momentum equilibrium equation, simply estimates the viscosity changes with depth. The result of regression curve is an exponential curve, and the viscosity in the bottom boundary layer bigger along with the bottom distance increasing but it does not include below boundary layer 3 m apart. With Zikanov et al. (2003) is apart from the instrument 1-17 m to the viscosity change to be approximately similar, only different in the bottom, the Zikanov curve is apart from below instrument 5 m, the viscosity become increase, but the viscosity of data analysis in this research goes on lessening to the instrument 3 m apart. |
