洋流可以被描述为流被迫在不同频率的振荡。在没有任何外部力量(风、摩擦),产生的流(惯性运动)[1],这是应对科里奥利和惯性之间的平衡。科里奥利参数,f,美元可以被描述为一个频率:一个包裹的有效行星转动频率的水。所以,f被称为科里奥利频率或美元惯性频率。有很多的例子在惯性频率电流不摆动。最简单的例子是潮汐。例如,在43.5 n,科里奥利频率是10美元^ {4}$ $ s ^{1} $,相当于[惯性段17.4 h] [2]。半日潮汐的主要组成部分,M_2,美元12.42 h,这导致频率大于惯性频率(中纬度地区)。发生的振荡频率大于科里奥利被称为super-inertial流动。另一方面,全日潮(例如,K_1,美元O_1)美元时期约24小时,因此美元有频率小于惯性频率(在中纬度地区)。 The oscillations that happen at frequencies smaller than Coriolis are called sub-inertial flows. [![http://www.boya-agl.st.ieo.es][3]][3]Flow spectrum showing energy peaks at certain frequencies: diurnal tides ($O_1, K_1$), semidiurnal tide ($M_2$), and Coriolis (inertial) frequency ($f$). In the real ocean, the balance between planetary vorticity (Coriolis) and inertia is only part of the story. There are usually other forces acting on the flow. For instance, when the balance is between Coriolis and the pressure gradient, we end up with the [geostrophic balance][4]. The resulting geostrophic currents can be described as a [zero-frequency motion][5] as there is no acceleration. Another important force is the effect of the wind. When we consider the balance between Coriolis (planetary rotation) and the frictional force (stress) caused by the wind, the balance results in [Ekman flow][6]. In the Ekman case, the mixing in the layer near the surface (boundary layer) needs to be considered. The same type of balance is present in the ocean in the vicinity of the bottom, as another boundary layer is established there for the flow to go to zero at the bottom. The resulting effect of these frictional forces is that the flow does no longer oscillate at inertial frequencies. In the paper you mention, they describe how the frictional effects near the boundary (Ekman balance) influence the interior flow. The interior of the ocean tends to be in geostrophic balance (frequencies smaller than inertial). The boundary flow effects tend to propagate into the interior modifying the geostrophic balance. A good example of this effect is Ekman pumping: cyclonic winds cause [Ekman transport][6], that in turn causes a surface divergence, and in order to balance the flow, result in vertical flow (upwelling). This effect is called Ekman pumping and modifies the interior flow to compensate boundary flows. [1]: http://marine.rutgers.edu/dmcs/ms501/2004/NotesWilkin/#_Toc89497136 [2]: http://www.physocean.icm.csic.es/Utilities/calculators/coriolis-en.html [3]: http://i.stack.imgur.com/j34Tq.png [4]: https://en.wikipedia.org/wiki/Geostrophic_current [5]: https://en.wikipedia.org/wiki/Geostrophic_current#Rotating_waves_of_zero_frequency [6]: https://en.wikipedia.org/wiki/Ekman_transport