The Agulhas Current System: A Key Control of the Atlantic System

建议研究控制阿古拉电流回射和环形成的低频变化的物理过程。这种变化是由内部过程和外部(对ACS)的影响造成的。我们将用动力系统理论的方法来研究环行星体的内部变异性，并发展一种新的回射和环形成的动力学理论。1979-2002年高水平(1/32)分辨率的海军分层海洋模式(NLOM)模拟的结果将被用来评估内部动力对气旋低频变化(相对于外部原因)的重要性。这项研究的动机是最近的观测表明，在阿古拉斯海流反反射区，上层输送存在很强的低频(年际到年代际)变率，并表明最大输送数值与环脱落事件之间有很强的对应关系。这也是因为最近的古海洋学替代分析表明，在冰川时期，阿古拉斯环的流动显著减少。然而，在冰川期接近尾声时，涌入的人数急剧增加。有人认为，由于环带携带的盐分异常，这种流入的增加有助于大西洋深水形成的重新开始。虽然目前对回射和环的形成都有独立的理论，但没有令人满意的理论将这两种现象联系起来并解释它们的年际变化。如果没有这些问题的答案，关于ACS行为的理论将是不完整的。对阿古拉斯流的动力系统研究也符合更广泛的尝试，即在西方边界流的海洋模型层级中系统地确定解的结构，特别是这些解的向复杂行为的转变。

It is proposed to investigate the physical processes controlling the low-frequency variations of the Agulhas Current retroflection and ring formation. This variability is caused by internal processes and external (to the ACS) influences. Methods from dynamical systems theory will be used to study the internal variability of the ACS and to develop a new dynamical theory of retroflection and ring formation. Output from a high horizontal (1/32) resolution Navy Layered Ocean Model (NLOM) simulation over the years 1979-2002 will be used to evaluate the importance of internal dynamics on the low-frequency variability of the ACS (versus external causes). This study is motivated by recent observations showing the existence of strong low-frequency (interannual-to-decadal) variability of the upper layer transport in the Agulhas Current retroflection region, and suggesting that there is a strong correspondence between maximum transport values and ring shedding events. It is also motivated by recent paleoceanographic proxy analyses indicating that during a glacial period, the Agulhas rings in- flux was significantly reduced. The influx, however, dramatically increased towards the end of the glacial period. It has been suggested that, due to salt anomalies carried by the rings, this increase of influx contributed to the re-start of deep water formation in the Atlantic. Although there are presently separate theories for both retroflection and ring formation, there is no satisfying theory connecting both phenomena as well as explaining their interannual variability. Without answers to these questions, the theory on the behavior of the ACS will stay incomplete. The dynamical systems study of the Agulhas Current fits also a broader attempt to determine systematically the solution structure, in particular the transitions to complex behavior of those solutions, in a hierarchy of ocean models of western boundary currents.