塔斯马尼亚岛至南极大陆断面风场的变化及其与锋的关系

本文利用WOCE塔斯马尼亚岛至南极大陆断面连续6年(1993-1998年)南半球夏季的上层温度数据确定了各锋位置,并对ERS-1/2卫星风场数据进行处理,获得该断面多年平均月风应力和风应力旋度,以及该断面风应力变化的时间序列。将各锋位置与局地的风应力和风应力旋度变化进行对比分析,探讨了两者之间的关系。结果显示,该断面纬向风应力和经向风应力均有周期为半年的季节变化,经向风应力变化超前于纬向风应力变化约1个月。风应力旋度有周期为2个月左右的变化。第一极锋(PF1)位置的经向季节变化幅度远小于气候月平均零旋度线的经向季节变化幅度,但位于零旋度线的平均位置附近。在PF1以北,向北输送的南极表层水(AASW)开始辐聚下沉,在下沉并北移的过程中与亚南极模态水(SAMW)相遇,SAMW与AASW之间温盐特征的巨大差异可能是导致亚南极锋(SAF)形成的主要原因。极锋区(PFZ,指极锋PF与亚南极锋SAF之间的区域)中辐聚大于辐散,部分辐聚的水体必定来自极锋以南向北输送的温度更低的上层水,对SAF水平温度梯度的形成和维持做出贡献。风应力旋度负最大值很可能决定了南极绕极流锋(SACCF)的强度:负最大值越大,埃克曼抽吸越强,南极绕极深层水(CDW)向海面涌升程度越大,CDW与变性南极绕极深层水(MCDW)之间温盐梯度的深度范围越大,锋强度越强。

VARIATIONS OF WIND AND THEIR RELATIONS WITH FRONTS IN THE SECTION BETWEEN TASMANIA ISLAND AND ANTARCTICA

The WOCE consecutive six-year temperature data in the upper layer of a section between Tasmania Island and Antarctica in the austral summers obtained by the French supply/research vessel "l'Astrolabeare" were used to determine the locations of fronts and to analyze their relation to the local variations of wind stress and wind stress curl derived from the ERS-1/2 satellite wind field data.The result shows that the zonal and meridional wind stress of this section has a seasonal cycle with a period of six months and the phase of zonal wind stress lags behind that of meridional wind stress for one month.Wind stress curl has a periodic variation of two months.The magnitude of seasonally meridional migration in the location of the primary Polar Front(PF1) is much less than that of the climatic monthly mean zero wind stress curl,but is near the mean position of zero wind stress curl.In the north of PF1 the Antarctic Surface Water(AASW) subducts as it continuously moves northward,and encounters the Subantarctic Mode Water(SAMW).The obvious difference in the characteristics of AASW and SAMW may result in the formation of the Subantarctic Front(SAF).Convergence is stronger than divergence in the Polar Front Zone(PFZ),indicating that a part of the converging water must come from the cold water transporting northward from south of PFZ and contribute to the formation and maintenance of the lateral temperature gradient of SAF.The negative maximum of the wind stress curl may determine the intensity of the Southern Antarctic Circumpolar Current Front(SACCF):The stronger the Ekman Pumping caused by the negative maximum of the wind stress curl is,the more intense the SACCF is.