衛星測高資料分析南海海潮、海水位、環流及渦漩

Abstract

南海為西太平洋之最大邊緣海，昔日對南海海潮、海水位、環流及渦漩研究大都以數值模式、船測或浮球觀測為主。近日因衛星測高技術已臻純熟，其量測之絕對海水位之精度已達數公分等級，且被應用於測算及監測寬闊大洋之中尺度海洋現象，因此本研究嘗試以衛星測高資料分析邊緣海(南海)之中尺度以上的海洋現象，探討其從高頻(9.9156天)至低頻(年際)的變化。 本文之主要研究課題為(1)以正交潮法和TOPEX/Poseidon(T/P)、European Remote Sensing-1/2(ERS-1/2)衛星測高資料建構2.5□×2.5□南海海潮模式，並以驗潮資料、T/P及ERS-2衛星測高資料分析南海海潮模式之精度。(2)以Morlet小波轉換、Daubechies小波多層解析轉換分析T/P衛星測高資料所得之南海海水位變化及其與ENSO( - Southern Oscillation)的關係。(3)以地轉流公式、渦漩動力特性模式、浮球觀測資料及T/P衛星測高資料探討南海地轉流及渦漩之季節性變化。(4)分析位於南海之海水位異常、風應力漩度、海面溫度、渦漩動能及比容異常於頻率域及空間上之相關性。 本研究得知(1)ERS-1/2衛星測高資料對提昇正交權精度之助益不大，其精度提昇的關鍵因素為T/P衛星測高資料。(2) T/P及ERS-2於南海深海之各交叉點差的RMS＜10cm。 (3)南海海潮潮型以全日潮為主，而東京灣受O1及K1分潮共振影響，其O1及K1分潮振幅較呂宋海峽附近為大。(4)當南海長期SLA之近似 小波係數，其曲率從負值轉為正值之時刻，即是以NINO3 SST為指標之 萌芽時刻，反之則為 萌芽時刻。(5)越南東方外海，在 事件時，第一個暖渦漩形成時間較早，當 事件結束後的夏季，第一個冷渦漩形成時間較晚。(6)越南東方海岸於8月形成向東噴射流，並沿緯度約12.5□N遠離越南海岸，此現象將持續至10月。 (7)風應力漩度與海水位異常在南海大部份海域，其半年及年分量的相關性達0.8以上。(8)南海南部海域，其海面溫度與海水位異常於年分量之相關性亦達0.8以上。

The South China Sea (SCS) is the largest marginal sea in the Western Pacific Ocean. In the past, numerical models, in situ observations and drifter data were used to study tide, sea level change, circulation and eddy over the SCS. Nowadays, the technique of altimetry is almost perfectly developed. The estimated accuracy of absolute sea level measurements by altimeter can achieve a few centimeters. The altimetry data is suitable for detecting mesoscale ocean variations. This study adopts altimetry data to analyze mesoscale ocean variations over the SCS in space and frequency domain, low frequency (inter-annual) to high frequency (9.9156 day). The major goals of this study can be summarized as follows: (1) The construction of 2.5□×2.5□ SCS ocean tide model by using orthotide approach, TOPEX/POSEIDON (T/P), and European Remote Sensing–1/2 (ERS-1/2) altimeter data as well as the validation of the SCS ocean tide model by using tide gauge data, T/P, and ERS-2 altimeter data. (2) Using Morlet wavelet transformation and Daubechies wavelet multiresolution to analyze the T/P-derived sea level change over the SCS, the relationships between ENSO ( - Southern Oscillation) and T/P-derived sea level change over the SCS. (3) Seasonal variations of circulation and eddy over the SCS by using formulas of geostrophic current, model of eddy kinematic property, drifter data, and T/P altimeter data were analyzed. (4) The coherency of sea level anomaly, wind stress curl, sea surface temperature, eddy kinematic energy, and steric anomaly in space and frequency domain is studied over the SCS. The important conclusions are: (1) The T/P altimeter data is more effective to improve the precision of orthoweight than that of the ERS altimeter data. (2) The RMS of the T/P and ERS-1 crossover difference of the deep ocean over the SCS is less than 10cm. (3) The SCS is mainly dominated by diurnal tide. O1 and K1 tide resonate in the whole Gulf of Tonkin and its largest amplitude is located at the vicinity of the Luzon Strait. (4) When the curvature of the look-like wavelet coefficient of the long term SLA over the SCS is turned from negative to positive, it is the budding time for which index is NINO3 SST. On the contrary, when the curvature is turned from positive to negative, it is the budding time for . (5) In the eastern sea of Vietnam, the formation of the first warm-core eddy at the event is earlier and that of the first cold-core eddy at the summer after the event is later. (6) On the coast of the eastern sea of Vietnam, the eastern jet is formed in August and leaves along the 12.5□N until October. (7) In the most area of the SCS, the coherency between the wind stress curl and the SLA, the annual and the semi-annual component, is above 0.8. (8) In the southern area of the SCS, the coherency between the sea surface temperature and the SLA, the annual component, is above 0.8.