Analysing Interannual Variation of Changjiang Diluted Water Spreading and Its Influencing Factors Based on Remote Sensing Observations

Expansion of the Changjiang Diluted Water (CDW) to the outer sea has a significant impact on the hydrobiological environment and material cycle in the Yellow Sea and the East China Sea. Based on 17 years of satellite fusion data from 1998 to 2014, this paper studies the inter-annual variations of the CDW spreading to the outer sea in summer, analyzes the influences of runoff and wind field on these changes. The result shows that the expansion path is mainly divided into three types: northeast-north type, northeast type and occasional type, in which northeast type is in the majority. The eastern boundary of the CDW expansion appears obviously inter-annual variations, and it mainly distributes in the range of 123°E to 126°E. The inter-annual variation of the expansion process is mainly reflected in the changes of expansion path and the distance of eastern expansion from July to August. The amount of runoff plays an important role in the distance of CDW expansion to the outer sea. When the runoff is large, the diluted water expands farther eastward, while when the runoff is small, the diluted water is limited near the Yangtze River estuary. The diversity of expansion process is obviously affected by wind direction. Southeast wind and east wind promote the expansion of diluted water in the northeast direction, and prevent the expansion in the southeast direction to some extent. Northeast wind prevents the expansion to the outer sea, forcing the diluted water staying near the Yangtze River estuary.