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

研究控制阿古拉斯流反射和环形成低频变化的物理过程。这种可变性是由内部过程和外部（对ACS）影响引起的。动力学系统理论的方法将用于研究ACS的内部变异性，并发展一种新的反射和环形成的动力学理论。高水平（1/32）分辨率海军分层海洋模式（NLOM） 1979-2002年模拟的输出将用于评估内部动力学对ACS低频变率的重要性（相对于外部原因）。最近的观测结果表明，在阿古拉斯海流反射区存在强烈的低频（年际至年代际）输运变率，并表明最大输运值与环脱落事件之间存在强烈的对应关系。最近的古海洋学代用分析也表明，在冰期，阿古拉斯环的通量显著减少。然而，在冰川期结束时，这种流入急剧增加。有人认为，由于环携带的盐分异常，这种流入的增加促成了大西洋深水形成的重新开始。虽然目前对反射和环的形成有不同的理论，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。没有这些问题的答案，关于ACS行为的理论将是不完整的。阿古拉斯海流的动力系统研究也适合于更广泛的尝试，即系统地确定解的结构，特别是那些解的复杂行为的过渡，在西方边界洋流的海洋模型层次中。

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.