北极超强气旋活动及其大气环流特征

北极极端气旋过程能够反映北极气候变化特征并对北极水文气象要素的调节具有重要影响，其活动及大气环流形势特征值得关注。利用美国国家环境预报中心(National Centers for Environmental Prediction，NCEP)与美国国家大气研究中心(National Center for Atmospheric Research，NCAR)提供的逐日再分析资料定义北极超强气旋(Arctic Super Cyclone, ASC)过程，结合美国国家冰雪数据中心(National Snow and Ice Data Center, NSIDC)基于NCEP/NCAR再分析资料追踪识别的北半球气旋及特征资料，分析了ASC的活动特征及其大气环流特征。结果表明：判别ASC的北极最低气压5%阈值具有显著的冬季低夏季高的单峰型季节变化特征，冬季ASC的强度远强于夏季；ASC多从大西洋扇区经北欧海−巴伦支海−喀拉海输入到极区，也存在少部分极区原生或太平洋扇区输入；ASC多生成于两大洋急流轴或急流出口区北侧，极少数生成于大陆或中低纬度，且绝大多数在极区消亡难以回到中纬度。极区原生ASC频数占总数约1/3，整体没有显著增减趋势，但长生命史ASC频数以0.49次/(10 a)的趋势增多，表明其持续时间增长。ASC频数与北极涛动(Arctic Oscillation, AO)在冬季相关性很好，其大气环流形势回归场中极区海平面出现低压低温异常，高空极涡加深且两大洋急流偏北，中纬度急流主轴偏弱；ASC的生成发展不仅有利于AO向正位相转变，同时AO正位相下也有利于ASC活动的增强，ASC活动是AO位相变化的潜在指标。

Arctic super cyclone activity and its atmospheric circulation characteristics

The extreme cyclones in the Arctic can reflect the characteristics of climate change in the Arctic and have important influence on the regulation of hydrometeorological elements in the Arctic. The characteristics of their activities and atmospheric circulation situation deserve attention. Using the daily reanalysis data provided by National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) defines the Arctic Super Cyclone (ASC) processes. Then analyze the activity characteristics of the ASCs and their atmospheric circulation characteristics based on the NCEP/NCAR reanalysis data of the National Snow and Ice Data Center (NSIDC). The results show that the 5% threshold of the minimum pressure in the Arctic for identifying ASCs have a significant unimodal seasonal variation characteristic that is low in winter and high in summer, which means the intensity of ASC in winter is much stronger than that in summer. Most of the ASCs are imported from the Atlantic sector to the polar region via the Nordic Sea, Barents Sea and the Kara Sea. Besides, a small part of the ASCs are imported from the original or Pacific sector. Most ASCs are generated on the north side of the jet axis or outlet area of the jet stream on two oceans. A minimal number of ASCs are generated in the continent or the middle and low latitudes. And the vast majority of ASCs disappear in the polar region and cannot return to the middle latitudes. The frequency of polar native ASC accounted for about one-third of the total, and there was no significant trend of increase or decrease overall. However, the frequency of long-life ASCs increased with a 0.49 times/decade trend, indicating their duration increased. There is a strong correlation between ASCs frequency and the Arctic Oscillation (AO) in winter. There are low-temperature and low-pressure anomalies in the polar region of the regression of the atmospheric circulation pattern. The upper polar vortex deepens and the two ocean jets turn northward, while the central axis of the mid-latitude jet stream is weak. The formation and development of ASCs are not only conducive to the transition of AO to the positive phase, but also conducive to the enhancement of ASC activity under the positive phase of AO, which is a potential indicator of AO phase change.