一个观察北极涛动与北大西洋涛动关系的典型个例

北极涛动与大西洋涛动是否属同一气候变率模态一直是北极涛动动力学研究方面的一个颇具争议的话题。文中通过对"0801南方雪灾"期间及其前后北极涛动与北大西洋涛动异常及产生原因进行个例分析,对两者之间的关系进行了讨论。首先使用交叉子波变换与子波相关方法分析了两者的相位关系。发现在30—60天时间尺度上北极涛动与北大西洋涛动相位相差90°或-90°。而在10 20天这一尺度上北极涛动与北大西洋涛动具有大致相同的相位。对北极涛动及北大西洋涛动形成的动力过程及其在拉尼娜背景下各自特点的分析表明,这种不同尺度上位相关系的差异来自于波-流相互作用动力学的局域性。众所周知,北极涛动的3个活动中心的形成与分别位于北大西洋、北太平洋和北极平流层的3个波流相互作用中心有关。而北大西洋涛动则主要与位于北大西洋的波-流相互作用中心有关。拉尼娜事件的出现通过影响太平洋急流及行星尺度的准定常波从而进一步强化了30-60天时间尺度上北极涛动与北大西洋涛动的这种差异。这主要是因为太平洋急流或准定常行星波在对流层中直接影响了位于该区域的北极涛动的活动中心。同时准定常行星波冬季向上传播至平流层并与平流层极涡相互作用从而也影响了北极涛动在北极的活动中心。而在10—20天时间尺度上的北极涛动与北大西洋涛动同步关系则说明它们都是北极涛动的另一活动中心即大西洋上同一波-流相互作用现象——天气波破碎的反映。基于上述分析.文中倾向于认同将北极涛动和北大西洋涛动区别考虑的观点。

A typical case for observation of the relationship between the Arctic Oscillation and the North Atlantic Oscillation

Whether or not the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) belong to the same mode of climate variability is a topic of long lasting disputation in the field of the AO dynamics. From the case study on the abnormal behaviors of the AO and the NAO during the period of freezing disaster around mid Jan initial Feb 2008 over the South China and their possible causes, this paper reviews the relationship between the AO and the NAO. The main analytical tools utilized in this study are cross wavelet transform and wavelet coherence. It is found that the phase of the AO leads or lags that of the NAO about 90° at the time scale of 30-60 days, while they are roughly in phase at the time scale of 10-20 days. Our analysis of the dynamical characters of both the AO and the NAO under the background of the 2007/08 La Nina event indicates that this variation of phase difference between the AO and the NAO with time scales origins from the regionality of wave flow interaction. As we all know, the formation of three centers of action of the AO has something to do with the intensive centers of wave flow interaction over the North Atlantic, the Northern Pacific and in the stratospheric polar vortex, respectively, while the NAO is mainly associated with wave flow interaction centers over the North Atlantic. By affecting the Pacific jet stream and planetary waves, the La Nina event intensifies this difference between the AO and the NAO at time scale of 30-60 days. The reasons are as below, the Pacific jet stream or planetary waves in troposphere can directly affect the Pacific center of action of the AO. Meanwhile, planetary waves propagating upwards also affect the polar vortex in the stratosphere, and then affect the Arctic centers of action of the AO. On the other hand, at the time scale of 10-20 days, the in phase relation of the AO and the NAO suggests that they may reflect the same physical phenomenon of wave flow interaction, i.e. the synoptic wave breaking process over the Atlantic, which is another center of action of the AO. Based on the analysis above, the results of this paper make us incline to regarding the AO and the NAO as different.