南极绕极流的表层环流结构和能量分布特征

利用历史的表面漂流浮标资料研究了南极绕极流的平均结构、变化规律和能量特征。强劲的南极绕极流沿着纬向从西向东流动,并伴随着复杂多变的海洋锋面,主导着整个南大洋的海洋环流系统。首先,标准方差椭圆表明,阿加勒斯回流和东澳大利亚暖流是南极绕极流重要的流量补充。在南半球的冬季,南极绕极流的流速随着西风的增强而增强。在南极绕极流经向摆动的影响下,流核上的经向流速比纬向流速具有更加不稳定的特征。另外,南极绕极流从非洲南部开始自西向东逐渐减弱。其次,从能量的角度讨论了南极绕极流的细节特征。平均动能、扰动动能及其均方根在流核区域都很强,扰动动能和平均动能比值的趋势恰恰相反,强(弱)能量分布区域的涡旋耗散反而比较弱(强)。除了扰动动能和平均动能的比值之外,所有的能量形式都呈现了从西向东减弱的趋势。涡动耗散对南大洋北部的平均动能影响更大。

NEAR-SURFACE STRUCTURE AND ENERGY CHARACTERISTICS OF THE ANTARCTIC CIRCUMPOLAR CURRENT

A strong nearly zonal Antarctic Circumpolar Current (ACC), combined with complex fronts, dominates the circulation system in the Southern Ocean. In this study, historical surface drifter observations collected from the Southern Ocean were used to study the near-surface structure, variability, and energy characteristics of the ACC. Standard variance ellipses indicated that both the Agulhas Return Current and the East Australian Warm Current are stable supplements of the near-surface ACC. During austral winter, current velocity increases because of the enhanced westerly wind. Stimulated by the meridional motion of the ACC, the meridional velocity shows greater characteristics of instability than the zonal velocity does over the core current. Additionally, the ACC exhibits an eastward declining trend in core current velocity from southern Africa. The energy distribution suggests that the mean kinetic energy (MKE), eddy kinetic energy (EKE), and are strong over the core current of the ACC. However, EKE/MKE suggests there is much less (more) eddy dissipation in regions with strong (weak) energy distribution. All energy forms other than EKE/MKE present west–east reducing trends. Furthermore, eddy dissipation has much greater effect on MKE in the northern part of the Southern Ocean.