Influence And Mechanism Of Arctic Winter Cyclone On Sea Ice

Cyclones are extremely important forms of extreme local atmospheric activity in the Arctic region.In recent decades,more persistent and strong cyclones have appeared in the Arctic Ocean,affecting the sea ice and surface climate from various aspects,resulting in frequent occurrence of extreme events.In addition,the magnitude and speed of loss of Arctic sea-ice have greatly increased,further strengthening the impact of cyclones on sea ice,forming a positive feedback effect.The change of Arctic sea-ice is of great significance to the global climate,economy,politics and military.As one of the important reasons affecting the change of Arctic cyclone,in-depth and comprehensive research is urgently needed.The paper uses ERA-Interim's mean sea level pressure data and TRACK from Hodges to extract the cyclone centers and trajectories in the Arctic Ocean(70-90°N)during the winter(December to April)of the past 40 years.The spatial and temporal distribution characteristics of cyclone(such as,cyclone frequency,radius,intensity,trajectory density,source density and extinction density,etc.)were also calculated.Using the sea ice concentration data provided by the National Snow and Ice Data Center(NSIDC)and the sea ice thickness data of ECCO V4r4,the impact of the cyclone on sea ice in the 4 days before and after the occurrence of the cyclone was analyzed.Using meteorological-related data(surface net shortwave radiation,net longwave radiation,sensible heat flux and latent heat flux,etc.)from ERA5 to analyze the impact of Arctic cyclones on sea ice during the winter of 1979-2016 from an atmospheric perspective.Using ocean-related data(stratification,3D temperature,mixed layer depth,etc.)from ECCO V4r4 to analyze the impact of Arctic cyclones on sea ice during the winter of1992-2016 from an oceanic perspective.The results of the study found that the long-term changes of Arctic winter cyclones in the past 40 years were not obvious,and the cyclone frequency,radius and intensity showed a weak downward trend.The spatial distribution characteristics of cyclone intensity and track density both show a gradual decrease from the Eurasian Basin side to the Canadian Basin side.For sea ice concentration,the abnormal decrease in sea ice concentration caused by cyclones mainly occurred on the day of the cyclone.At the same time,the existence of the cyclone would inhibit the increase of sea ice concentration in the days following the occurrence of the cyclone.In terms of sea ice thickness,the slowing down or even thinning of sea ice thickness in the Barents Sea mainly occurred on the day of the cyclone,while the change in sea ice thickness in most of the eastern Arctic mainly occurred a few days after the occurrence of the cyclone.Regardless of sea ice concentration or sea ice thickness,the decrease in sea ice on the day of the cyclone was mainly due to the anomalous increase in the surface net longwave radiation caused by the anomalous increase in downward longwave radiation.One of the mechanisms for the reduction of sea ice in the 4 days after the cyclone is that the cyclone reduces the depth difference between the depth of upper Atlantic water and the depth of the mixed layer(AWmld)on that day,which promotes the upward transfer of ocean heat,and eventually affect sea ice days after the cyclone.The sharp decrease in sea ice concentration in the northern Barents Sea and southern Kara Sea on the day of the cyclone,and the change in sea ice thickness in the northeastern and western Barents Sea,both related to increased heat transfer from the ocean upwards caused by cyclones.The paper also discusses one reason why the cyclone causes the upward transfer of ocean heat: the kinetic energy carried by the cyclone when the cyclone occurs,on the one hand,weakens the upper layer of most of the Arctic Ocean,thus deepening the mixed layer;on the other hand,it is converted into the potential energy of the ocean,increasing the upward Ekman pumping strength,thereby uplifting the Atlantic water.The combined effect of the two weakens the halocline,favoring the transfer of heat from the deeper warm water to the mixed layer and ultimately to the sea ice.