利用電磁垂直剖面探測浮標資料分析南海內孤立波的訊號

Abstract

南海(South China Sea)為全球內孤立波(Internal solitary wave, ISW)規模最大、能量最強的海域之一。此海洋現象內部之垂直流速(Vertical velocity)遠高於一般海洋環境，其威力足以對區域內之人為建設構成潛在風險。為了更加了解此具危險性之海洋現象內部的動力結構，本研究致力於提出一套新的儀器觀測策略，應用電磁垂直剖面探測浮標(EM-APEX Float)於南海蒐集之資料進行對內孤立波的識別分析，此浮標為一種具自主垂直剖面能力的海洋觀測儀器，其1至2公尺的高解析度特性，能更加清晰的呈現內部之動力結構。由於此儀器並不具備直接量測垂直流速的能力，本研究以浮標在水中的垂直運動速度為代理指標。然而，浮標的垂直運動變化受浮力調控(Buoyancy adjustment)與海流推動共同影響。為確認該變化並非由浮力因素所致，本研究進一步引入浮標運動狀態相關之數項參數進行回歸統計，特別是與浮力作用密切相關的浮標旋轉速度(Rotation rate)，藉此多參數的統計結果以識別受海流推動造成之異常運動，並據此作為初步判斷內孤立波存在的條件。在此基礎上，分析浮標於該段落所量測之水文資料，探討與內孤立波相關的動力結構特徵，包括等密度面位移振盪(Isopycnal displacement)與東西向流速(Zonal velocity)之垂直分布特性。最終，透過浮標的運動行為與水層物理結構的雙重驗證，以辨識出資料中的內孤立波事件。本研究為首次應用EM-APEX Float於南海進行內孤立波之觀測，將在結尾透過分析識別的結果，建立出一套適用於往後資料中事件辨識的參考準則，為該儀器在南海內孤立波研究上的應用潛力提供分析實證與技術基礎。

The South China Sea is one of the regions where internal solitary wave (ISW) exhibit the largest scales and strongest intensities globally. The vertical velocity within such phenomena far exceeds typical oceanic background conditions and poses potential risks to man-made structures. To better understand the internal dynamics of this hazardous process, this study proposes a new observational strategy utilizing the Electromagnetic Autonomous Profiling Explorer (EM-APEX) float, which collected high-resolution (1–2 m) data in March 2022 in the South China Sea. As the float cannot directly measure vertical velocity, the analysis uses the float’s vertical motion speed (dP/dt) as a proxy. Since the float’s vertical motion is governed by both buoyancy adjustment and external flow, a regression analysis involving motion-related parameters, particularly rotation rate, which reflects buoyancy-driven movement, is conducted to isolate segments where vertical motion is primarily driven by environmental forcing. These identified segments serve as initial indicators for potential ISW events. Further analysis of float-measured hydrographic data focuses on ISW structures, including isopycnal displacement and the vertical profile of zonal velocity. Through combined evaluation of float motion and water column structure, ISW events are successfully identified. This study represents the first deployment of EM-APEX floats for ISW observation in the South China Sea, and based on the analytical results, proposes a reference framework for future ISW event identification using EM-APEX float’s data, offering empirical and technical support for its application in internal solitary wave research.