Analysis of the characteristics of offshore currents in the Changjiang (Yangtze River) estuarine waters based on buoy observations
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摘要: 为了揭示长江口外海域海流的特征及其季节和垂向变化规律,于2006年8月1日-2007年7月31日在长江口外海域(平均水深约46.0m)利用大型浮标进行了1年的分层海流流速流向观测。结果表明:(1)该海域海流为顺时针方向的旋转流,在垂向上流向较一致,季节变化不显著。(2)长江口外海域水平流速总体较大,夏季表层最大流速为128.5cm/s,冬季最大表层流速为105.5cm/s;垂线平均流速相近(差异<8.0 cm/s),夏季流速最大为47.0cm/s,冬季为40.8cm/s。小潮的平均流速为26.5cm/s,大潮平均流速为小潮的2倍。(3)剖面各层流速垂向差异明显,最大流速出现在表层(春季和冬季)或次表层(夏季和秋季),最小流速均出现在底层;各层的最大平均流速为57.9cm/s,出现在夏季的18m层。(4)垂线平均余流为7.5~11.3 cm/s,春季最强冬季最弱;春季和冬季各层余流均为东向,夏季和秋季基本为东北向或北向。(5)观测海域海流受长江冲淡水、台湾暖流、季风、潮汐等动力作用的共同制约。Abstract: A buoy of 10 m in diameter was used to record the current speed and direction in a vertical profile in the offshore area of the Changjiang (Yangtze River) Estuary (with an average water depth of 46.0 m) for one year. The results include:(1) the currents rotate clockwise and the current direction is consistent in a vertical profile without clear seasonal variations. (2) The horizontal current speeds are generally high, with a maximum of 128.5 cm/s occurring in summer and 105.5 cm/s appearing in winter commonly close to the surface. The average current speeds in the vertical profile fall in the same range (the differences are less than 8.0 cm/s), with the maximum of 47.0 cm/s occurring in summer and 40.8 cm/s in winter. The average current speed during spring tides is twice that during neap tides (26.5 cm/s). (3) Significant differences of speeds are observed in the vertical profile. The maximum current speed occurs at either surface (spring and winter) or sub-surface (summer and autumn), with the minimum current speed appearing at the bottom. The maximum average current speed of all layers is 57.9 cm/s, which occurs in the 18-m layer during summer. (4) The average speed of the residual currents ranges from 7.5 cm/s to 11.3 cm/s, with the strongest occurring in spring and weakest in winter. The residual currents of all layers are eastward during spring and winter, whereas northeastward or northward during summer and autumn. (5) The currents in the offshore of Changjiang Estuary are impacted collectively by diluted Changjiang River discharge, the Taiwan Warm Current, monsoon and tides.
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