博士 / 國立臺灣海洋大學 / 環境生物與漁業科學學系 / 97 / The major scope of this dissertation is focuses on the analysis of high-resolution (1.1 km) sea surface temperature (SST) data derived form satellites. This study reveals unprecedented finer structures of SST fronts by applying an entropy-based edge detection method to long-term (1995-2008) satellite SST images. Therefore, we are able to further investigate the SST fronts related with coastal fishery. There are 4 well detected frontal bands identified through the very high-resolution data and systematic analysis:
(1) The Mainland China Coastal Front is a long frontal band with larger SST gradient magnitude (>0.2 oC/km) along the 50-m isobath near the Chinese coast. It is a boundary between Mainland China Coastal Current and warmer water in the Strait. This front reaches the northern edge of the Taiwan Bank in winter, but the front is difficult to see when the cold current retreats to the north in spring and summer.
(2) The Peng-Chang Front forms year-round along the Peng-Hu Channel and extends northwestward parallel to the edge of Chang-Yung Ridge. In winter, it is a weak front with moderate SST GM (<0.15 oC/km), but in summer its southern part along the Peng-Hu Channel is enhanced because of the cold upwelling water of Kuroshio Branch Current on the eastern coast of Peng-Hu Islands.
(3) The Taiwan Bank Front is a broad frontal band with SST gradient magnitude less than 0.2 oC /km. It also forms year-round and evolves along the southern edge of the Bank (i.e., the 50-m isobath). In winter, the frontal band spreads widely over the Bank and connects with the southward extension of the Mainland China Coastal Front. In summer, it is formed by the Taiwan Bank upwelling which is originated from the ascending bottom currents of the northern SCS.
(4) The Kuroshio Front is formed in the area between the Kurohsio Current and the shelf water north of Taiwan. The Kuroshio Front with SST gradient magnitudes of 0.2oC/km is formed along the 100-m isobath. Based on our result, the formation of this front is attributed to interaction between Kuroshio, inshore cold shelf mixing water and its subsurface upwelling water on the offshore side. Therefore, high concentrations of Chl-a (2.0 mg/m3) are found at the warm front and the offshore cold front.
The application of SST front to coastal fishery shows that in summer, high CPUE (Catch per unit effort, kg/day/boat) of squid always occurs along the northern edge of Taiwan Bank with SST from 27.25 to 27.5oC. The locations of high CPUE in July correspond well with the sharp SST front band (>0.15oC/km) on the northern Taiwan Bank, but CPUE of higher than 50 kg/day/boat is rarely observed in September while the northern part of SST front is not clear present. It is suggested that SST front with SST gradient magnitude lager than 0.15oC/km can be an indicator of the congregation of squid around the Taiwan Bank.
It is interesting that an exceptional cold water intrusion into the southern TS has been observed in February 2008. The warm Kuroshio Branch Current which dominants the water around the Chang-Yuen Ridge year round was restricted to the southern Strait. Comparing the long-term wind speed with SST, it is shown that in January to February of 2008, the strong northeasterly wind of higher than 6 m/s lasted for 30 days while the SST decreased from 20.2 to 12.6oC (a drop of > 7.6oC); however, SST then increased gradually while the wind speed decreased. It is suggested that in the winter of 2008, the La Nina event results in strong and continuous northeasterly may drive the cold Mainland China Costal Current more southward to penetrate into the Peng-Hu Channel from north of the Chang-Yuen Ridge and a portion of this current intruded eastward south of the Peng-Hu Islands. The low SST event also significant damage on marine lives and cage aquaculture, more than 130 tons of resident and coral reef fishes died during the cold SST event. This suggested the strong wind blowing for 12 days with the distance of 20oC isobath referring to central PHI (23.5oN, 119.5oE) lower than 3.4 km could be the indicators of cold water intrusion. It could be the warning for fishery management agencies to prevent the impact of cold SST on fishery damages.
| Identifer | oai:union.ndltd.org:TW/097NTOU5451013 |
| Date | January 2009 |
| Creators | Yi Chang, 張懿 |
| Contributors | Ming-An Lee, 李明安 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 110 |
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