缓变风场驱动下正压环流中的多涡结构

MULTI-EDDY STRUCTURE IN BAROTROPIC CIRCULATION DRIVEN BY SLOWLY VARYING WIND

利用正压涡度方程,研究了缓变风场驱动下水平尺度 1000km平底方形海盆中海洋环流的响应。结果表明,缓变风场驱动下海洋环流的响应是多涡型的,线性情形下多涡结构表现为共振受迫Rossby波;非线性情形下受迫Rossby波被扭曲,多涡结构是由受迫Rossby波和次海盆尺度的惯性再循环共同构成。无论是稳定风场还是缓变风场,非线性作用越强,环流越趋于不稳定;非线性作用强且水平耗散作用弱时,非线性不稳定过程可能完全掩盖了变化的风旋度向海盆涡度输入的影响,此时风的变化对环流型式不再重要。

A barotropic vorticity equation is used to study the response of ocean circulation driv- en by slowly varying wind (SVW) in a closed square basin with flat bottom topography and a horizontal scale of 1000km. The results show that the ocean circulation driven by SVW exhib- its multi-eddy structures (MES). In linear cases the MES is the resonant forced Rossby wave with the same frequency as that of wind stress. In nonlinear cases the forced Rossby wave is distorted and the MES is the combination of the forced Rossby wave and the sub-basin-scale in- ertial recirculation excited in the northwest or southwest corner of the basin. No matter driven by steady or slowly varying wind stress, the mean circulation would be destabilized in the case of stronger nonlinear and weaker dissipation. In this case, the instable process enshrouds the influence of the varying wind stress curl on the circulation, as a result, the time variation of wind stress is not important for the pattern of the circulation any more.