Impact Of Extreme Cyclones Entering The Arctic From The North Atlantic On Winter Climate In China

Based on the datasets of ERA-Interim reanalysis data and the observation data from China meteorological stations,146 Extreme Cyclones(ECs)occurring in the mid-high latitude North Atlantic are identified by a objective recognition and tracking algorithm and statistical analysis is used in order to gain the the temporal and spatial characteristics of ECs during 1980/1981-2015/2016 in winter.Based on the K-means clustering and the composite similarity index,ECs are classified according to different tracks and circulation situations and the impacts of ECs with different tracks on climate in China are explored by further analysis and comparison.The statistical results show that the average lifetime of ECS is 3.9 days,and the trend of ECs' frequency decreases slightly.The number of ECs which occur in the south of Greenland or the east of North America and move northward along the east side of Greenland is the largest.As for the subsequent weather in China,the ECs corresponding to the occurrence of cold spells account for around 63.70%,and the ECs which occur in the south of Greenland and move northward along its east side are more likely to correspond to cold spells,accounting for 80.77%.Further study shows that the occurrence of ECs(lag 0 day)is accompanied by a significant anomalous warming and high-pressure anomaly and two Rossby waves in high latitude and middle latitude are strengthened.Accompanied by the development and northward extension of high-pressure,the polar vortex splits at around lag 9 day,and meanwhile low-pressure system on the east of the high-pressure strengthens and extends eastward over China through energy dispersion.As a result,there id cold anomaly in China with a lag of 1-2 weeks.By comparison,the circulation situations and anomalous Rossby waves are different at lag 0 day with the discrepancy of ECs tracks and thus the weather in China is also different.The first type of ECs moves northward along the mid-west of Greenland.Subsequently the stronger cold anomaly appears in China at lag 14 day and the cold spells concentrate on the northern China.The second type of ECs moves northward along the east of Greenland.Correspondingly the whole country suffers from cold spells with a long duration and wide scope especially in the south of China,but its intensity is weaker slightly than the first type's.The third type of ECs moves northward along the west of Europe continent with the weaker anomalous warming and anomalous Rossby waves,and thus have a little influence on cold spells which concentrate on the southwest of China.As for the ECs with similar tracks but occurring in higher latitude,the circulation systems are more northerly,stronger and moving faster,and thus the cold spells in China are earlier,wider and stronger.