Vacillations in a Shallow-Water Model of the Stratosphere
Vacillations in a Shallow-Water Model of the Stratosphere
复制标题
平流层浅水模型中的波动
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
D. Waugh
中科院分区：
文献类型：
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作者：
P. Rong;D. Waugh
研究了在一定的地形强迫幅值范围内，地形强迫和松弛不随时间变化到一个恒定平衡态的浅水模式中极涡的演化。对于小的强迫强度，极涡的边缘只有微弱的扰动，涡区面积保持不变，而对于大的强迫强度，则存在涡旋破裂和重塑的循环(纬向风在西风和东风之间摇摆)。对位涡等值线内质量的分析表明，这些抖动是由于弛豫和超扩散引起位涡等值线上质量通量的异相变化所致。在强涡旋阶段，Rossby波破裂产生一个小尺度的PV级联，这些小尺度特征最终被超扩散所消除。这会导致高PV等值线内的质量减少，最终导致涡旋的破坏。相反，在无涡旋的阶段，存在很弱的PV梯度，弱的Rossby波活动，以及很少的小尺度PV级联。然后，由于非绝热弛豫项的质量通量，涡旋和PV梯度被重建。这些结果表明，水平PV结构可能在三维模式和真实平流层中的涡旋破裂和恢复过程中起着重要作用。
The evolution of the polar vortex in a shallow-water model with time-independent topographic forcing and relaxation to a constant equilibrium state is investigated for a range of topographic forcing amplitudes. For small forcing amplitudes there are only weak disturbances on the edge of the polar vortex and the vortex area remains constant, whereas for large amplitudes there are cycles where the vortex breaks down and then reforms (and zonal winds vacillate between westerlies and easterlies). Analysis of the mass within potential vorticity (PV) contours shows that these vacillations are due to out-of-phase variations in the mass fluxes across PV contours due to the relaxation and to hyperdiffusion. During the strong vortex stages Rossby wave breaking produces a cascade of PV to small scales, and these small-scale features are eventually eliminated by hyperdiffusion. This causes a decrease in the mass within the high PV contours and ultimately the destruction of the vortex. In contrast, during stages with no vortex there are very weak PV gradients, weak Rossby wave activity, and little cascade of PV to small scales. The vortex, and PV gradients, are then reestablished by the mass fluxes due to the diabatic relaxation term. These results suggest that the horizontal PV structure may play an important role in the vortex breakdown and recovery in three-dimensional models and in the real stratosphere.