周期为1 a的长周期分潮Sa主要由气象因素的变化引起。基于长江河口段5个潮位站多年水位资料，分析了长江河口段潮汐的分潮组成、潮汐类型和变形、主要天文分潮和气象分潮Sa的时空变化特征，并初步探讨了各分潮时空变化的原因。结果表明，长江河口段多为非正规半日潮，潮汐变形显著；由口门向内陆上溯，天文分潮振幅减小、迟角增大，而气象分潮Sa振幅增大、迟角趋小；Sa分潮振幅年际变化与大通站最大日距平流量变化趋势一致，河口段的Sa分潮受径流影响显著。%On the basis of water level data of 5 tidal stations along the Yangtze River estuary, the tidal constituents, tidal type and distortion, as well as the temporal and spatial variation of mainly astronomical tides and Sa constituent in Yangtze River estu-ary were analyzed, and the reasons for the temporal and spatial variation of tidal constituents were also primarily discussed. The analytic results show that, the tide at Yangtze River estuary usually is irregular semi-diurnal tide with significant distortion. From the estuary to the upstream, the amplitude of astronomical tide decreases, the phase lag increases, on the contrary, the am-plitude of Sa constituent increases, and the phase lag decreases. The inter-annual variability of Sa constituent amplitude reveals the same changing trend with the maximum daily anomaly flow of Datong Station, and the Sa constituent at estuary area is signifi-cantly affected by runoff.
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