中国海和泰国湾海域海平面的经向涛动

卫星高度计遥感海面高度距平资料(1992-2012年)的分析结果证实中国海(渤、黄、东海及南海)和泰国湾作为一个半封闭的狭长水域,其海平面存在显著的南北经向涛动。涛动呈现明显的季节性,冬季南高北低,夏季北高南低,以渤海和泰国湾的海平面高差作为涛动的测度,其多年平均波动幅度达63cm,较差超过80cm。时间序列分析显示,在季节尺度上这一涛动几乎完全受东亚季风的支配,表明东亚季风的局地强迫是造成季节涛动的主要原因。进一步的分析发现,除季节波动之外研究海域海平面的经向涛动还存在明显的年际变化。不过,与季节尺度的波动有所不同,经向涛动的年际变化不仅是东亚季风区局地作用的结果,而且与太平洋海盆尺度的大气强迫有关,其作用与季风在同一数量级。涛动的年际变化大致滞后各气候因子两个月。采用多输入线性模型做偏相关分析筛选的结果显示,除东亚季风指数之外,研究海域的海平面涛动指数主要与太平洋的南方涛动指数(SOI)和西太平洋遥相关指数(WP)相关。这表明外部强迫既来自热带,也来自中纬度。南方涛动所导致的赤道海域海平面的东西向年际涛动,以及中纬度西风急流年际波动对西北太平洋海平面的作用,都有可能导致研究海域海平面经向涛动的年际变化,其机制有待进一步探讨。

The meridional sea level oscillation of the China seas and the Gulf of Thailand

Analyses of sea level anomalies(SLA) from satellite altimetry,ranging from 1992 to 2012,indicate that,as a semi-enclosed narrow water body,the China seas (consisted of the Bohai Sea,the Huanghai Sea,the East China Sea,and the South China Sea) and the Gulf of Thailand are subject to significant meridional sea level oscillation. The north-south SLA seesaw is strongly seasonal,with sea level being high in the south but low in the north during winter seasons,and vise versa in summer. The sea level difference between the Gulf of Bohai and the Gulf of Thailand is taken as a measure of the oscillation,which has a range of over 80 cm and a climatological annual mean of 63 cm. The analysis shows that,in the seasonal time scale,the meridional oscillation is almost totally dominated by variations of the East Asian monsoon,which indicates that monsoon is the main cause of the seasonal seesaw. Further analysis reveals that,in addition to seasonal variation,the meridional sea level oscillation is also subjected to considerable interannual variation. Unlike the oscillation in the seasonal time scale,its interannual variation appears correlated no only with the fluctuations of the East Asian Monsoon but also with the basin scale variation of the Pacific. The influences of remote forcings are comparable with that of the East Asian monsoon,and the seesaw generally lags two months behind the atmospheric forcings. The results from a multi-input,linear partial coherience model shows that,among the mumberous input factors other than the East Asia Monsoon Index,the interannual variation of the sea level oscillation index is correlated with SOI and WP. It is thus suggested that,in addition to the East Asian monsoon,remote forcings are from the tropics as well as the mid-latitude. The east-west sea level seesaw in the tropical Pacific associated with the southern oscillation,and the possible effects of interannual migration of the mid-latitude East Asian jet stream on the sea level,are both possible to cause interannual variation of the north-south sea level seesaw in the area. Further investigation is needed to determine their mechanism.