| Summary: | 博士 === 國立臺灣大學 === 海洋研究所 === 90 === Using the climatology of wind and ocean thermal field, the characteristics of basin-wide variation in the South China Sea (SCS), especially annual evolution, were examined in the primary stag of study. The correlation between both and the impact of El Niño event on the SCS wind variability were also investigated. The spatial and temporal variation of the SCS upper ocean current and temperature and Kuroshio in the Luzon Strait (LS) were explored using the observation of 12 mooring data sets in the following stage. Finally, the dynamics of the SCS upper ocean current and thermal variation were explained by the result of numerical model (MICOM).
During the 1997/1998 El Niño event, a weak northeast (NE) monsoon was found during the El Niño year, though results did not indicate the existence of a weak southwest (SW) monsoon nor the intensification of the NE monsoon during the following La Niña period. The effects of El Niño on monsoons in the SCS appear to vary with each event. The correlation between wind stress curl and changes in upper ocean heat content exhibited a large but negative value in the central basin extending from east of Vietnam to Luzon, indicating the critical role of Ekman pumping on the annual variation of upper ocean heat content in the central basin.
In combination with the moored current velocity and Sb-ADCP composite current velocity spatial distribution in the LS, a conclusion could be made. The Kuroshio intruded persistently into the SCS through the central LS. It had small annual, but large intra-seasonal variation. The mechanism of Kuroshio intrusion in the LS is dominated the difference of sea surface height between north and south of strait. The difference is mainly caused by the variation of thermal field in the south LS.
From the model results, it explained that the vigorous temperature fluctuation in the SCS was primarily induced by the motion of warm and cold core which had large vertical and horizontal temperature gradient at its marginal region. It also re-produced the abnormal warming in the thermal field during the 1997/1998 El Niño event.
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