Jets and Topography: Jet Transitions and the Impact on Transport in the Antarctic Circumpolar Current
Jets and Topography: Jet Transitions and the Impact on Transport in the Antarctic Circumpolar Current
复制标题
DOI：
10.1175/jpo-d-11-0135.1
复制
发表时间：
2012-06
影响因子：
3.5
通讯作者：
A. Thompson;J. Sallée
中科院分区：
文献类型：
--
作者：
A. Thompson;J. Sallée
南大洋的南极绕极流（ACC）自然地适用于使用纬向平均框架的解释。然而，在陡峭和复杂的测深障碍物周围航行表明，当地的动态可能与纬向对称模型所描述的动态相去甚远。在这项研究中，观测和数值计算结果表明，纬向不对称性，地形的形式，影响全球流动结构和传输特性。这些结论是基于一套超过150万虚拟漂流轨迹平流使用卫星测高派生的表面速度场跨越17年。重点是在网站上的"交叉前"运输所定义的运动在选定的海面高度等值线，对应于喷气机沿着大部分ACC。交叉前交换是本地化的背风水深特征与超过75%的交叉事件发生在对应于只有20%的ACC的带状范围的区域。这些意见激发了一系列的数值试验，使用一个简单的，纬向不对称的地形，这往往会产生过渡，在前面的结构沿着通道的两层准地转模式。值得注意的是，政权发生的相干射流的平衡数量是一个功能的经度和运输障碍不是周期性的。射流重组是通过涡动通量发散来进行的，涡动通量发散作用于射流的平均流的加速和减速。由于地形转向引起的斜压性增加，涡动能在地形下游被放大。高涡流动能和再循环特征的组合增强了颗粒交换。这些结果强调了在制定一致的环极定义的ACC前线的复杂性。
The Southern Ocean’s Antarctic Circumpolar Current (ACC) naturally lends itself to interpretations using a zonally averaged framework. Yet, navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models. In this study, both observational and numerical results indicate that zonal asymmetries, in the form of topography, impact global flow structure and transport properties. The conclusions are based on a suite of more than 1.5 million virtual drifter trajectories advected using a satellite altimetry–derived surface velocity field spanning 17 years. The focus is on sites of “cross front” transport as defined by movement across selected sea surface height contours that correspond to jets along most of the ACC. Cross-front exchange is localized in the lee of bathymetric features with more than 75% of crossing events occurring in regions corresponding to only 20% of the ACC’s zonal extent. These observations motivate a series of numerical experiments using a two-layer quasigeostrophic model with simple, zonally asymmetric topography, which often produces transitions in the front structure along the channel. Significantly, regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic. Jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets. Eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering. The combination of high eddy kinetic energy and recirculation features enhances particle exchange. These results stress the complications in developing consistent circumpolar definitions of the ACC fronts.