The variation of currents in Shenao Bay－observed by GPS drifters

• Main Authors: Tung-Chien Cheng, 鄭東健
• Other Authors: Jian-Hwa Hu
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/42037984475987871057

碩士 === 國立臺灣海洋大學 === 海洋環境資訊學系 === 93 === Shenao Bay is a C-shaped small bay in the north of Taiwan. In the west of the bay, Shenao peninsula projects out from the coast, making the near shore current meandering. The warm plume of a power plant and the freash water of Taganlin Creek make the surface water with high temperature and low salinity, being the main factor of the variation of flow field of inner and outer bay. On December 1st, 2005, there once made an experiment of observation on the inner bay with several apparatus, including GPS drifters, high-frequency Acoustic Doppler Profilers (ADP), CTD, and tide gauge. The surface flow field displayed by drifter trajectories obviously varied with tide. Its speed is in general slow of about 10~20 cm/s. After the climax of flood-tide, the surface water of the bay entirely moves towards the inner coast. In the slack water period, a stream towards the bay mouth appears around the oil harbor, and develops a temporary anti-cyclonic motion in the ebb tide. At the low tide, the surface water begins to deliver to the bay mouth, and is forced to turn 90 degrees towards Shenao peninsula by the northwest flood steam at the primary stage of flood tide. In the middle of the flood-tide, the flood stream of outer bay is highly developed, and there begins to appear a cyclonic eddy inside the bay. At the end of flood-tide, the eddy becomes the most mature. When the flow speed is fast, the surface flow field is nearly the same as that of the 2.5 m depth subsurface flow field, but there also exists two layers of water flow interacting with each other but moving in opposite directions. The drifter trajectories are derived from GPS directly, while the 2.5 m depth flow field is the low-frequency statistics computed by the synoptic process. Their comparison proves that the ADP measurement is authentic, and also the Bay is of stratification. The acquisition of CTD on the vertical structures of temperature and salinity proves that in the inner bay there exists a high temperature and low salinity water layer of only about 1m depth.