赤道东太平洋温度锋附近的混沌输运与混合

Chaotic Transport and Mixing near the Eastern Equatorial Pacific Thermal Front

运用 Mc Creary和 Yu(1992 )的非线性 2 12 层模式的积分流场 ,研究了混沌混合与输运对海水及要素浓度的输运和混合问题。模式结果显示混沌混合区主要分布于赤道东太平洋不稳定区及东、西边界附近 ,中西太平洋的大部分区域为非混沌区。释放在混沌区内的示踪团随时间的弥散过程要较非混沌区内的示踪团复杂的多。因多模态不稳定波动的共同作用 ,尤其是在赤道上经向运动最强的 Yanai波的加入 ,使得赤道不稳定区的流体以混沌混合的方式均匀地弥散开 ,趋向于粗粒 (coarse- grained)意义下的均匀化。并有大量释放于赤道东太平洋不稳定区的示踪质点越过赤道进入对面半球。背景辐散流的加入能将部分示踪点输送出混合区使其不加入均匀化过程 ,故最后混入另一半球的质点数少于半数。过赤道交换速率则主要由混沌混合的强度有关。

Nonlinear 2 12 layer model of McCreary and Yu (1992)is used to study the effect of chaotic transport and mixing on the transport and mixing of sea water and tracers. In the model, the main chaotic regions exist in unstable zone and the eastern and western ocean boundary. The dispersion process of a cloud of passive tracers in chaotic region is more complicated than that in the non chaotic region. Due to the interaction of multi mode unstable wave, especially the joining of Yanai wave, whose meridional component is the strongest, the fluid in equatorial unstable zone disperses uniformly in the chaotic mixing style and becomes gradually uniformed in a sense of coarse grained. The chaotic stirring induced by the unstable wave makes quite a part of sea water cross the equator and leads to effective mass exchange across the equator. The joining of background flow makes some of the tracer particles go out the chaotic region. So these particles don't join the uniform process. The result shows that the particles number across the equator is less than the half. The rate of exchange across the equator is mainly related to the strength of chaotic mixing.