从牛顿力学认识罗斯贝波的振荡机理及其回复力
On the Oscillation Mechanism and Restoring Force for Rossby Waves
中文摘要：
蔡鸣和黄渤华[1]近期对罗斯贝波形成机制提出了一个全新的物理解释：对地转流而言，科氏参数纬向变化与地形坡度一样，起着机械障碍作用，可使沿上坡（下坡）方向的地转流产生质量辐合（辐散）。由于不能继续沿等压线上（下）坡流动，部分由机械障碍所引起的质量辐合（辐散）会导致上坡区（下坡区）气压升高（降低），剩余部分则改道穿越等压线，转为非平衡流。由机械障碍激发的非平衡流又会受到科氏力作用。当科氏力将非平衡流转向与等压线平行时，作用在被转向气流的科氏力已与原上坡区（下坡区）的气压升高（降低）后所产生的气压梯度力平衡，于是科氏力不再继续起转向功能，也就是说科氏力的转向功能仅发挥了一半，便与气压变化的水平梯度平衡了。由非平衡流变为与等压线平行气流，从而形成新的上坡（下坡）地转流，完成一轮完整振荡。这种振荡包含了“障碍物”所激发的质量辐合／辐散及因其而改道穿越等压线的非平衡流，以及半周期科氏转向，故称为“机械－科氏振荡”，其回复力为“障碍物激发的半周期科氏力”。经历一个完整振荡循环后，在北（南）半球面朝上（下）坡方向，与新气压场平衡的新地转上下坡流型将出现在原地转上下坡流型的左侧。而科氏参数引起的“β-障碍”在南北半球均沿各自的极地方向抬升，因此该振荡激发的波型，即罗斯贝波，总是向西传播。
中文关键词：
罗斯贝波， 科氏力，地转平衡，非平衡流
KeyWords：
Rossby waves, Coriolis Force, geostrophic balance, unbalanced geostrophic flow
Abstract：
The recent work of Cai and Huang[1] presents an entirely new view on the physical origin of Rossby waves: the presence of the latitudinal variation of the Coriolis parameter and/or a sloped bottom terrain serves as a mechanical barrier that causes a mass convergence (divergence) when a geostrophic flow crosses it uphill (downhill). Part of the mass convergence (divergence) causes pressure rising (falling) along the uphill (downhill) pathway while the remaining part is detoured as an unbalanced flow that crosses isobars. This mechanically excited unbalanced flow is subject to a “half-cycle” Coriolis force that only turns it to the direction parallel to isobars without continuing to turn it further back to its opposite direction because of the balance nature of the flow parallel to isobars. Such oscillation, involving a barrier-induced mass convergence, a mechanical deflection, and a halfcycle Coriolis deflection, is referred to as a mechanical-Coriolis oscillation with a “barrier-induced half-cycle Coriolis force” as its restoring force. Through a complete cycle of the mechanical-Coriolis oscillation, a new pattern of the geostrophic flow, which is in balance with a new pressure pattern, emerges to the left of the existing flow when facing the uphill (downhill) direction of the barrier in the Northern (Southern) Hemisphere. Due to the latitudinal variation of the Coriolis parameter, the β-barrier is always sloped towards the pole in both hemispheres, responsible for the westward propagation of Rossby waves.