Study Of Sea Level Change And Its Influencing Factor In The China Sea Based On Nineteen Years’ Altimeter Data

Sea level rise leads to natural hazards such as coastal erosion and storm tide,which bring great threat to human survival environment. So it is of great value tostudy sea level change. The rising rates, cycle features, seasonal signal, low-frequencysignal and intra-seasonal signal are analyzed by using the1993-2011sea levelanomaly data from AVISO. Combing Ishii temperature and salinity data, OISST seasurface temperature data, surface wind stress data, and SOI index, the influencingfactors of seasonal signal, low-frequency signal and intra-seasonal signal are explored.The main research results are as follows.The mean sea level rising rate is4.99mm/a in China Sea. The sea level risingrate is4.9mm/a in the South China Sea,3.28mm/a in the East China Sea and3.1mm/a in the Bohai Sea and Yellow Sea. The rising rate is different in differentregions and is higher in south than in north.The most significant cycle of sea level variations in the China Sea is one year.The other cycles of sea level variations in the South China Sea are0.5a,1.5a,2.5a,7aand so on. The other cycles of sea level variations in the East China Sea are1.2a,1.8a,3a and so on. The other cycles of sea level variations in the Bohai Sea and Yellow Seaare1.5a,2a,3a and so on.The seasonal sea level variations are significant, which is mainly composed ofannual signal. The amplitude of annual signal is lower form north to south. Thedistributions of annual phase are different between in the open sea and in the coastalwaters. The phase is lower from north to south in the open sea, while it is lower fromsouth to north. The contributions of annual signal to variance are bigger in the opensea than in the coastal waters. The main driving powers of seasonal signal in sea levelchange are wind and thermal expansion, and the driving mechanisms are different indifferent regions and seasons. The leading role is also changing with the change oftime and space. In general, the sea water driven by wind is dominant in the coastal area, and the sea level is driven by both in the open sea. Besides, the seasonal signal isinfluenced by Kuroshio in the Kuroshio region.The low-frequency signal of sea level variations in both the South China Sea andthe East China Sea is closely related to ENSO. There is certain relevance betweenthe low-frequency signal of SSL and that of SOI. And the low-frequency signal ofSSL is also related to that of SLA. What’s more, the time delay between SSL andSOI is consistent with that between SLA and SOI. Then, we deduce that SSL is thebridge between SLA and ENSO. Therefore, ENSO can influence sea level changethrough steric sea level change in both the South China Sea and the East China SeaThere are obvious intra-seasonal variation characteristics in the sea level of theSouth China Sea, the Bohai Sea and the Yellow Sea. The EOF analyzing results showthat there are several intra-seasonal cycles in the South China Sea, the Bohai Sea andthe Yellow Sea. The spatial distribution of variable EOF analysis modes is different,which indicates that the intra-seasonal sea level change is influenced by a few factors.The intra-seasonal components of surface temperature and wind are also significant.The intra-seasonal cycles of surface temperature and wind are similar with that ofintra-seasonal sea level signal. Therefore, sea surface temperature and wind areimportant influencing factors of intra-seasonal variability of sea level.