The Research Of Characteristic And Relationship Of Mesoscale Eddies And Polar Lows In Nordic Seas

Nordic Seas are the transitional region between the North Atlantic Ocean and the Arctic Ocean, also are one of the most important regions that drive global ocean thermohaline circulation and for the formation of North Atlantic deep water, playing an important role in the study of global climate change. The movement of mesoscale eddies and polar lows in the Nordic Seas have important influences on the current circle and climate changes. Currently, people have not much understood for their time-pace distributions and movement characteristics. So, based on the methods of verification of mesoscale eddies and identification of polar lows with high-resolution satellite altimeter and mean sea level pressure database, respectively, mesoscale eddies and polar lows occurred between 2000 and 2014 in the Nordic Seas have been comprehensive counted in this paper. Characteristics of the mesoscale eddies and polar lows, including their accounts, spatial distributions, lifetimes, radius ranges, moving trends and speeds and eddy energy, have been analyzed in detail,then a preliminary study on the respond of mesoscale eddies to polar lows was given.Firstly, based on the method of eddies determination of Nencioli et al and variation characteristics of them in Nordic seas, correlation parameters were confirmed, and by using geostrophic current anomaly data(UV)between 2000 and 2014,which are extracted from the global ocean high-resolution satellite altimeter database, 1129 cyclonic eddies and 1267 anti-cyclonic eddies which with lifetime longer than 4 weeks(including 4 weeks) were detected and identified. About 5.8% of these eddies could lasted for longer than 10 weeks(including 10 weeks). The number of eddies in Spring and Summer are more than in Autumn and Winter. Most of these eddies concentrate in the east of 0° longitude, mainly distribute in warm current region in sheet form and few eddies concentrate in the west of 0° longitude, mainly distribute in cold current region in strip form. Influenced by the large-scale circulations,eddies in this ocean region mainly move around in Norwegian coastal area,moving speed of most eddies is about 5cm/s. Some eddies closed to the coastal zone move slowly, seem rotating related to the local topography.Secondly,based on the method of cyclones determination of Zahn et al and mean sea level pressure and water depth and topography data, the statistics characteristic of polar lows shows that: between 2000 and 2014, 140 polar lows occurred in the Nordic Seas, about 89% of them could active lasted for 1 to 3 days. Polar lows mostly occurred in November to March,distance travelled mainly about 500-750 km,speed was much small. Affected by the Atlantic warm current and its branches in Norway and the Arctic cold air, polar lows in this region concentrate in the vicinity of Lofoten basin. Polar lows moving from north to south are mainly impacted by the cold air from the Arctic,and distribute in the east of 0° longitude. Most Polar lows in this region mainly generate from the northeast of Iceland and the vicinity of Lofoten basin,and decay along the Norwegian coast and its northwestern.Lastly, the analysis of upper circulation characteristics implies that the wind field caused by polar lows mainly has a cyclonic structure, and the variation of sea fluxes driven by the wind stress curl mainly present in the southward transport of cold current and northward transport of warm current,in which the northward transport of warm current could reach 5Sv,and the southward transport of cold current could reach 25 Sv. Combined with North Atlantic Oscillation index, mesoscale eddies activity and the northward transport of the warm Norwegian Atlantic current both influenced by North Atlantic Oscillation and polar lows. Compared to North Atlantic Oscillation,eddies activity in high eddy kinetic energy region mostly impacted by polar lows.The research shows that the statistical result of mesoscale eddies and polar lows in Nordic Seas based on the method of previous researcher are reliable and credible in this paper. The analysis of their characteristics and response relationship has great significance for the knowledge of the activity conditions of mesoscale eddies and polar lows,including their accounts,spatial distributions,intensities,size,speed and tracks,as also as further studies of moisture and heat transport in high latitude and facing with extreme weather and climate change.