Study on mechanism of formation and variability of the Arctic Oscillation

北极涛动是冬季北方热带外海平面气压变化的最主要模态，是中纬度地区与北极地区的跷跷板式变化。它有一个相当的正压结构，它有一个信号到平流层下部。这种模式类似于北大西洋涛动，但它更环形和全球性。Thompson和Wallace（1998）将其命名为北极涛动（Arctic Oscillation）。对模拟结果的合成分析表明，北极涛动的优势是由波-平均流相互作用引起的。北极涛动正、负位相的转换主要是由行星尺度波动引起的，天气尺度波动也有一定的贡献，冬季北极涛动与平流层极地夜间急流振荡有关。当极区夜间急流较常年偏强时，对流层北极涛动有向正位相转换的趋势，实际上在平流层突然变暖后，对应于极区夜间急流较弱和平流层北极涛动负位相，对流层北极涛动有向负位相转换的趋势，从而在中纬度地区造成强的寒冷天气。北极涛动与欧亚大陆、日本北方和鄂霍次克海冬季气候有较好的相关性。通过对鄂霍次克海海冰范围的分析，发现海冰范围与北极涛动（也与北大西洋涛动）有很好的相关性。

The Arctic Oscillation the most dominant variation mode of the wintertime sea-level pressure in the Northern extratropics and it is the seesaw variation between the midlatitudes and the Arctic region. It has an equivalent barotropic structure and it has a signal up to the lower stratosphere. This mode resembles the North Atlantic Oscillation, but it is more annular and global. It was named as the Arctic Oscillation by Thompson and Wallace(1998).A perpetual February simulation by an AGCM clearly showed the Arctic Oscillation is not a forced mode but an internal mode of the atmosphere. The composite analysis of the simulation results showed the dominance of the Arctic Oscillation is caused by the wave-mean flow interaction. Mostly planetary-scale wave contributes to the transition to positive and negative phases of the Arctic Oscillation and the synoptic-scale wave also contributes to the transition.The perpetual February experiment also shows that the wintertime Arctic Oscillation is related to the polar night jet oscillation in the stratosphere. When the polar night jet is stronger than normal, the Arctic Oscillation in the troposphere tends to shift to posituve phase.In reality after the stratospheric sudden warming, which corresponds to weak polar night jet and negative phase of the stratospheric Arctic Oscillation, the tropospheric Arctic Oscillation tends to have a negative phase, which bring severe cold weather in midlatitudes.In interannaul and intraseasonal time scales, the Arctic Oscillation has a good correlation with the winter climate over Eurasia, northern Japan and Sea of Okhotsk. Analyzing the sea ice extent over Sea of Okhotsk, it is found that the sea ice extent has a good correlation with the Arctic Oscillation(also with the North Atlantic Oscillation).