Sea Level Change In The South China Sea And Its Relations To The The Steric Height Variation And Wind

The purpose of the research on sea level change is to grasp its discipline and forecast its variation in the future and evaluate its influence on the living environment of human beings. In this paper, the variations of sea surface height (SSH), steric sea level (SSL) and wind in the South China Sea are analyzed based on the altimeter data of Topex/Poseidon (T/P) satellite, temperature and salinity data of Ishii and wind data from ICOADS database.The result shows that the SSH of the SCS rises at a rate of 4.7mm/yr from 1993 to 2002. In most area, both the SSH and SSL are rising but the rising rate is different from place to place. In the northeast where the SSH rises very fast, the rising rate can reach 10.0mm/yr while in the southwest, the rate is very small and the rising rate of the SSH there is less than 2 mm/yr. During 1996/1997, both the SSH and SSL in the SCS have a significant rising.During 1993~2002 , the SSL change associated with temperature variation dominates the change of the SSH with a contribution of 89.4%. In the northeast, the SSL changes in phase with the SSH with a contribution of 130.8% to the latter while in the southwest, the SSL leads the SSH by about four months with a contribution of 33.3%. The effect of the steric variability on the SSH in the northeastern SCS is stronger than that in the southwestern SCS.The range of the seasonal variability of the SSH is about 4 cm, smaller than that of the SSL which is about 6 cm, the phase of the SSL leads the SSH by about two months. In the northeastern SCS, the range of the seasonal variability of the SSH and the SSL are both about 10 cm; In the southwestern SCS, the range of the two are 9 cm and 4 cm respectively.One reason for the range of the SSH being smaller than that of the SSL is that there exist prominent spatial changes (maybe reverse in phase from one place to another) in SSH, which is much weaker in SSL. So the range of the SSH become smaller after averaged over the whole SCS. Another reason is that in the southwestern SCS, the part of the SSH change caused by the circulations and characters of climate is opposite in phase with the steric effect.The SSL during 1955~2003 shows obvious ascending trend, the ascending rate calculated from Ishii(2005) and Levitus(2005) data are 0.4 mm/yr and 0.3 mm/yr respectively. Moreover, the SSL shows striking interannual and decadal variability. The SSL in the SCS during 1955～2003 has a variability of 20-year period and the spatial distribution of its linear variation trend presents prominent time-dependent regional characteristics.By analyzing the relation between the wind stress curl and the non-steric sea level, we found that in area of west to Luzon in winter and summer, and east to Vietnam in spring and autumn, the effect of the wind stress curl on the non-steric height is obvious. But on the north of 18°N, this effect is much weaker. In the other area of SCS, the effect is also weaker. The circulation becomes dominant. Besides the SSL, the longitudinal and zonal wind stress are both important to SSH. The correlation coefficient between non-steric height and longitudinal wind stress is about 0.7 with consistent phase. The phase of the non-steric height leads the zonal wind stress by about two months, and the correlation coefficient is 0.7.