Analysis Of Temporal And Spatial Characteristics Of Sea Surface Temperature And Sea Surface Salinity In The Adjacent Area Of The Yangtze River Estuary

The Yangtze River estuary is close to the mainland.The geographical environment and complex circulation structure make the sea area near the Yangtze River Estuary show unique characteristics of temperature and salinity distribution.It is important to study Sea Surface Temperature(SST)/ Sea Surface Salinity(SSS)changes and freshwater detection in the adjacent waters of the Yangtze River Estuary in terms of improving our understanding of the characteristics of temperature and salinity changes,maintaining the ecological environment of the coast,and promoting sustainable economic development.This paper takes the adjacent waters of the Yangtze River Estuary as research area,uses multi-source data to analyse the spatial-temporal changes and the influence factors of SST in the research area.The SSS distribution and exploration of Yangtze River freshwater in summer are studied.The marine and meteorological factors that may affect the SST and SSS in the adjacent waters of the Yangtze River Estuary are also analyzed.This work provides scientific data and research basis for further study of process and mechanism of temperature and salinity change,provide reference and support for further marine dynamic environment and short-term prediction in research area.The main works of this paper are as follow:(1)This paper analyses the temporal-spatial variation of SST in the adjacent area of Yangtze River Estuary using MW-IR SST products.The results show that,the SST in the research area of the Yangtze River Estuary is generally between 15-25?,the temperature difference in the South and North can exceed 10?.The SST is lower in northwest and higher in southeast in the Yangtze River Estuary.There are warm water tongues formed by the expansion of Taiwan Warm Current,Tsushima warm current and Yellow Sea Warm Current,cold-water tongues formed by the southward invasion of the cold water in Yellow Sea.The warming/ cooling of SST trend in the study area is accordant,shows a heating trend.The SST in the study area shows a south-north inverse distribution characteristic with 32° N as the boundary,when the SST is warming in the North,the SST is cooling in the South.The SST in the adjacent sea area of the Yangtze River Estuary also has a negative distribution in the Korean Peninsula and the sea area near Chejudo,and a positive distribution in other sea areas.The SST cooling trend in winter,and the warming trend in summer is the most significant in four seasons.(2)The present paper uses the measured salinity data and MODIS Aqua Rrs data to establish the SSS linear retrieval model in the adjacent area of Yangtze River Estuary.Then the model is validated by independent measured data.The root mean square error of the model is 1.55 psu,the correlation coefficient is 0.80.The model is extended to MODIS Terra,Sea Wi FS and VIIRS SNPP Rrs for Multi-source satellite SSS fusion.The spatial coverage of fused satellite SSS data is about 10% greater than that of single-satellite retrieved SSS data.The multi-annual mean SSS in summer is 30.8psu.The spatial distribution of the SSS in the Yangtze Estuary research area has lower values nearshore and higher values offshore.The SSS gradually rises from nearshore to open waters and there is an obvious low-salinity tongue in the Yangtze Estuary.Types of freshwater expansion in the Yangtze River are northeast expansion,north-northeast expansion,east-northeast expansion,bidirectional expansion,and non-directional expansion.(3)This paper analyses the influence factors of SSS/ SST in Yangtze River Estuary.The results show that,SST is positively correlated with current velocity,East Asian summer monsoon index and land temperature around the Yangtze River Estuary,while SST is negatively correlated with wind speed and East Asian winter monsoon index.Among them,the East Asian winter monsoon have a significant impact on the SST change in the Yangtze River Estuary.The eastward expansion of freshwater flows of the Yangtze River into the sea is mainly affected by the runoff of the Yangtze River,while a southerly wind and northeastward flow in the research area are the main factors that affect the diversion of the Yangtze River to the northeast.In summer,the expansion of the Yangtze River freshwater has an impact on SST and SSS in the research area.As a whole,SSS is positively correlated with SST,and the eastward expansion distance of freshwater is negatively correlated with SST.