Dynamical Elliptical Diagnostics of the Antarctic Polar Vortex
Dynamical Elliptical Diagnostics of the Antarctic Polar Vortex
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DOI：
10.1175/jas-d-19-0232.1
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发表时间：
2019-03
影响因子：
3.1
通讯作者：
M. Mester;J. G. Esler
中科院分区：
文献类型：
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作者：
M. Mester;J. G. Esler
椭圆诊断提供有关北极和南极平流层极涡行为的动力学和气候学信息。在这里，Kida的模型描述了线性但可能不稳定的背景流中均匀涡旋的演变，用于解释1999-2018年冬末南极涡旋的观测演变。Kida的模式有振荡的解决方案，可以经历一个振幅分叉，这是一个简单的模式的涡分裂平流层突然变暖（SSW）的发病。用资料同化的方法求出了与观测值一致的Kida方程的解。相平面分析表明，涡旋振荡幅度的年际变化很大。2002年是唯一观测到涡旋分裂南极SSW的一年，发现该系统在9月下旬穿越了相空间中的分界线，与SSW振幅分岔相关。数据同化的输出是涡旋所经历的线性背景流。这种线性流动的旋转分量与嵌入反气旋背景中的涡旋一致。时间平均应变流是弱的，但有一个明确的方向，由于行星尺度地形和海陆对比的存在下，固定强迫一致。随时间变化的应变流是比较大的幅度，说明在对流层顶水平发生的湍流动力学的行星尺度分量的相对重要性。因此，与北方半球不同，未来南极涡旋分裂的方向不一定与2002年分裂的方向一致。
Elliptical diagnostics provide dynamical and climatological information about the behavior of the Arctic and Antarctic stratospheric polar vortices. Here Kida’s model, describing the evolution of a uniform vortex in a linear, but possibly unsteady, background flow, is used to interpret the observed evolution of the Antarctic vortex in late winter during 1999–2018. Kida’s model has oscillatory solutions that can undergo an amplitude bifurcation, which serves as a simple model for the onset of vortex-splitting stratospheric sudden warmings (SSWs). A data assimilation method is used to find solutions of Kida’s equations consistent with the observations. A phase-plane analysis reveals large interannual variability in the amplitude of oscillations of the vortex. In 2002, the year of the only observed vortex-splitting Antarctic SSW, the system is found to cross a separatrix in phase space, associated with the SSW amplitude bifurcation, in late September. An output of the data assimilation is the linear background flow experienced by the vortex. The rotational component of this linear flow is consistent with the vortex being embedded in an anticyclonic background. The time-mean strain flow is weak but has a clear orientation, consistent with the presence of stationary forcing due to planetary-scale topography and land–sea contrast. The time-varying strain flow is comparatively large in magnitude, illustrating the relative importance of the planetary-scale component of the turbulent dynamics occurring at tropopause level. Unlike in the Northern Hemisphere, therefore, the direction of future Antarctic vortex splits will not necessarily align with the direction of the 2002 split.