Abstract: The expansion of the Changjiang diluted water (CDW) is a dominant hydrographic phenomenon in the East China Sea, which is mainly in the shape of plume. However, there are also some low-salinity lenses (LSWLes) in partial time of some years. The observations show that there wasn’t LSWL in August 1976 while there was in August 1977. The numerical simulations in this paper explained these phenomena. The strength of tide from the end of July to August in 1976 was similar with that in 1977, so as the runoff. And there were both processes of strong leaning south wind from July 21 to August 4. Then the mechanism why there wasn’t LSWL during the process of the strong leaning south wind in summer 1976 is analyzed. The strong leaning south wind and its direction of south-south-east were helpful for pushing CDW northeastward and cutting it to form LSWL. The strongest leaning south wind was from July 26 to 30 when it was the time from neap tide to spring tide, which was the main reason of no LSWL. And the strong leaning south wind was slightly weaker in 1976 than that in 1977, thus it didn’t made so significant effect on LWSL formation as that in 1977.

Key words: the Changjiang diluted water, low-salinity water lens, wind, dynamic mechanism, numerical simulation