Impact of the interannual and interdecadal anomalous circulation on the circumpolar cyclone activity
The main purpose of this study is to examine the influence of the different atmospheric oscillations on circumpolar cyclone activity. Many studies have been dedicated to the theorems about the El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Arctic Oscillation (AO) by using observational data and simulations. These atmospheric oscillations have a regional or global impact on climate change. This study's results show that the interannual and interdecadal variations revealed from the circumpolar cyclone activity can be affected by the anomalous circulation pattern under different atmospheric oscillations. The case numbers of circumpolar cyclones generated in East Asia have a high correlation with the ENSO events and those cyclones generated in North America with the NAO extreme phases. Furthermore, the life cycle of circumpolar cyclones matches with the variation of ENSO, and the length of the propagation fluctuates with the AO index. An in-depth comparison between the above observed interannual and interdecadal phenomena and the Empirical Orthogonal Function (EOF) results found that: 1. The composite anomalous circulation patterns are able to represent the major atmospheric oscillation confirmed by the mathematical method. 2. The anomalous AO interdecadal circulation shows the circumglobal oscillation of the polar vortex, combining the regional ENSO and NAO effects. Although the ENSO and NAO have regional influence on the general circulation in the North Pacific and North Atlantic, the AO revealed from the polar vortex oscillation is still the primary impact on the propagation of circumpolar cyclone activity, especially for the interdecadal variation.