Research On Temporal And Spatial Variations Of Sea Surface Height In The East China Sea

Due to global warming,sea levels continue to rise.Sea level variation is very sensitive to the climate change.The global sea level rise has accelerated in the past two decades.Furthermore,the sea level along China's coast is rapidly rising.Due to the rise in sea levels,marine catastrophic events such as storm surges,coastal erosion,and seawater intrusion,are more likely to occur thereby threatening economic development and human living environment in the coastal areas.Studying sea level variations and the main forcing mechanisms and forecasting the sea level trend can help prevent marine catastrophic events effectively.Therefore,research on sea level variations can contribute significantly to disaster assessment.Based on AVISO satellite altimetry data,the seasonal and spatial patterns of the sea surface height anomaly(SSHA)during 1993-2016 in the ECS were determined.and discusses the impact of different ocean hydrodynamic processes and ENSO processes on SSH in the ECS were analyzed by using wavelet analysis and EOF methods.The variations of SSH related to the thermo-steric effect and the ENSO were discussed.The SSH of the ECS had a significant seasonal variation,which is lower in the winter and the spring and is higher in the summer and autumn.The peak values of SSH lagged behind that of the sea temperature for a month.In the whole,the SSH is lower in the northern part and higher in the southern part of the ECS.The SSH had obviously regional distributions in the different seasons due to the effect of depth and ocean dynamical processes.Wavelet analysis results show that the cycle feature of the sea level are la and 2.2a.The cycle characteristics of the SSH interannual variability in different sea areas are generally similar,interannual oscillations are most obvious,and the over 95%confidence level is basically between 1.5-3 years.There are certain differences in the spectral peaks of each sea area,among which the interannual variation period corresponding to the peak of the Bohai Sea(BS)spectrum is 1.8 years,and the Yellow Sea(YS)and the East Sea(ES)are 2.3 and 2.0 years respectively.In the ECS,SSH has a linear rate of rise of 3.16 mm·yr-1 over the 24 years,and it has been affected by the stagnation of global warming since 2000.The rate of sea level rise has dropped to 2.8 mn·yr-1.The sea level rise rate of ECS is more spatially different.The sea level rise rate in the coastal areas of the Yellow Sea and Bohai Sea is relatively large,with a maximum of 7 mm·yr-1,while the sea level rise rate in the wide sea is 2-4 mm·yr-1.The rate of increase in the sea near the Taiwan Strait is about 2 mm·yr-1.EOF first three modes show that the seasonal variation of the thermos-steric effect and the dynamical processes and the interannual variation of ENSO had the important effects on the variations of SSH in the ECS.The steric sea level is similar to that of SSH in the ECS.The seasonal variation is significant,and the seasonal spatial distribution is similar.The TSLA year is slightly worse than that of the SSHA.Meanwhile,the seasonal variation of the SSHA has a certain lag behind the seasonal change of the TSLA.The EOF analysis results show that the first two modes are seasonal modes,the cumulative contribution rate is 77.5%,the third mode is the ENSO mode,and the cumulative contribution rate is 12.2%.Analyze the spatial distribution of the correlation coefficient between TSLA and SSHA.The correlation coefficient is relatively high,reaching over 0.7 in the BS and YS,and which is between 0.4 and 0.6 in the eastern and southern of Taiwan islands.It is negatively related in the Taiwan Island and the correlation coefficient is lower than 0.2.The SST(sea surface temperature)variation is affected by solar radiation in the ECS,and the seasonal variation is significant.In February,it was the lowest in the whole year and highest in August,and the spatial distribution was low in the south and high in the north.The results show that the correlation between SSH and SST is greater than 0.6 in the most of sea areas of ECS,and corresponds to the SSH anomaly EOF first mode abnormally high value area.Therefore,the seasonal variations of the sea level are mainly affected by the SST and the sea surface seasonal winds in the ECS.Seasonal variations of the sea level in the Taiwan Straits,including the coast of Fujian and Zhejiang,are mainly affected by the monsoon.Seasonal variation of sea levels are subject to the SST seasonal variations in the other sea areas of ECS.The amplitude of SSH seasonal variations was significantly affected by ENSO events.During the E1 Nino event,the amplitude of interannual changes in sea level decreased,while the La Nina event increased;at the same time,the SSH interannual change in the East China Sea had a better response to ENSO events.The maximum correlation coefficient between SSH and SOI was-0.40 in the ECS,and the SOI was lead SSH 3 months.