Baffin Bay Sea Ice Export And Impacts Of Extratropical Storm Tracks

As an essential climate indicator,sea ice plays a vital role in regulating surface albedo,flux exchange between atmosphere and ocean,freshwater circulation and global thermohaline circulation.It is of great scientific significance to gain insight into the changes in sea ice and corresponding forcing factors.Cyclones are an essential and strong form of local atmospheric activity in the Arctic and are closely related to changes in Arctic sea ice.The Polar Pathfinder Daily 25km EASE-Grid Sea Ice Motion Vectors product and satellite-derived daily Sea Ice Concentration provided by the National Snow and Ice Data Center(NSIDC)are used to estimate sea ice area flux(SIAF)through three gates within the Baffin Bay.Based on the reanalysis data obtained from European Centre for Medium-Range Weather Forecasts(ECMWF),an automatic cyclone identification and tracking algorithm was used to extract the center position and trajectory of the cyclones in the middle and high latitudes(30°N-90°N)of the northern hemisphere in the past forty years,and the corresponding features including duration,travel speed,travel distance,deepening rate,intensity and radius were also obtained.This study investigates the change of the cyclone activities and sea ice export in the Arctic region over the past four decades(1979 to present)and explores the regulation mechanism of Arctic cyclone activities on sea ice export in the Baffin Bay.The results of the study point to that the SIAF of the three key passages of the Baffin Bay from 1979/1980 to 2017/2018 are characterized by obvious seasonal cycle,high interannual variability and clear long-term trends.Normally,the daily SIAF from June to October is negligible;it starts to increase sharply in the colder months and attains its maximum in January or February.Decadal alterations in the daily SIAF fields over the periods before and after 2000 are prominent during the cold months with increased daily sea ice area flux in recent years.Besides,a significant interannual variation in the monthly SIF for each passage is detected.On average,the annual(October-September)SIAF through the north gate(NG),Lancaster Sound(LS)and south gate(SG)with large interannual variability are 242×10~3 km~2,-1.7×10~3 km~2and 247×10~3 km~2,respectively,for which winter(December to March)accounts more than 70%.Significant increasing trends are found for the winter SIAF through LS and NG,which are chiefly related to the increasing ice motion while no noticeable trend is observed for SIAF through SG.Besides,during 1979/1980-2017/2018,the life span of most cyclones in winter and summer in the middle and high latitudes of the northern hemisphere is about 1-7days,with an average effective radius of 300 km-650 km,a travel distance mainly within 4000 km and a moving speed less than 100 km/h.The location and characteristics of cyclones in the study area are of spatial heterogeneity.More cyclone centers,genesis and lysis are identified in the area around 70°N in the Baffin Bay,south of the Davis Strait and east of Greenland.Track density is highest in the domain from the east of North America,extending to the southwest of Iceland.Stronger cyclones are mainly occurring in the Davis Strait,the Labrador Sea and the Nordic Seas,while storms in the Baffin Bay are relatively weak.The trend pattern of cyclone center count is spatially dependent,with a significant increasing trend of total center count in the overall study area.Finally,the results of a case study and composite analysis indicate that cyclones may have persistent and significant impacts on sea ice movement(SIM)and concentration(SIC),thus changes in SIAF.However,the regulation is spatially dependent.When SIAF via SG is large in winter,the east of Greenland witnesses more cyclones while fewer cyclones occur in the region west of Baffin Bay.Based on cyclone intensity variations,two critical areas are screened out,one around Baffin Island and(80°W-60°W,60°N-70°N),and the other over the southern Labrador Peninsula(70°W-50°W,40°N-60°N),winters with lower cyclone intensity in the regions mentioned above have larger SIAF through SG.Cyclone-induced strong wind exerts strong influences on sea ice to alter its motion and distribution.In winter,cyclones deform the ice cover and,as a response,produce cracks,leads and polynias.However,the openings could rapidly refreeze merely in a few days after the cyclone,so the cyclone-induced impact of SIAF is almost solely attributable to the dynamics factors.