A Study On The Regularity Of Winter Anticyclone Activity In Eurasia In The Past 40 Years

A new objective anticyclone identification method based on the Mask R-CNN is proposed in this paper.By comparing the results of the new method with manual analysis,as well as studying cases that cold highs affect the regional weather conditions through the morphological changes,the reliability of the new algorithm and its advantage in the anticyclone shape identification can be verified.By using the new proposed algorithm,the 1978-2017 winter Eurasia anticyclone dataset can be obtained and we analyzed the anticyclone activities and their corresponding circulation characteristics from the perspective of synoptic climatology.In addition,the influence of the autumn sea ice condition in the Barents Sea on the anticyclone activities are explored,and the numerical model is used for its verification.The main results are as follows:(1)A new objective anticyclone identification method based on the Mask R-CNN is proposed to improve the description ability of the two-dimensional shape characteristics.By comparing the anticyclone identification results from 2008 to 2012 obtained by this new method with manual analysis,it is found that the new method can recognize most of the anticyclones identified by manual and maintain the consistency on shape description,and the new method can also supplement the identification results.By using this new method,the two-dimensional influence domains of the southeastward-extending Siberian cold highs(SEESCHs)that affect the winter temperature changes in north and east China can be well marked,and its intensification period that has a substantial effect on regional weather can be selected for research.(2)Through statistic,the Siberia is the main active region as well as generation and extinction area for winter Eurasian anticyclones.Anticyclones passing through this region mainly are synoptic systems and tend to generate and diminish in local place,while some anticyclones move eastward to the East Asian coast and other places to disappear.The strength of the Siberian anticyclones is positively correlated with the accumulation of cold air mass in Eurasia in winter,and negatively correlated with the temperatures in the mid-latitude region of Eurasia.Temperatures in mid-latitude region of Eurasia(especially in Siberia)are significantly lower when the Siberian anticyclone activities are intensified.In addition,anticyclones passing through Siberia can be divided into three types: the eastward moving type,the northwestsoutheast type and the local type.These three types of anticyclones correspond to the different circulation patterns and the energy dispersions of upstream Rossby waves may have an important influence on the movement and maintenance of the three types of anticyclone tracks.(3)The autumn sea ice in the Barents Sea-Kara Sea basically show an antiphase change with the cold air mass carried by the winter anticyclones in the mid-latitude Eurasia.Further research found that the autumn sea ice in the Barents Sea decreased significantly in recent decades.And the absorbed solar shortwave radiation increases due to the broader open water induced by the retreat of sea ice in the Barents-Kara Sea,which is conductive to the abnormal heat transfer from the ocean to the atmosphere in later winter.These can stimulate the quasimeridian Rossby wave train from the Barents Sea-Kara Sea area,which is benefit to the local type anticyclone activities.By using The Community Atmosphere Model version 6(CAM6),it is found that the frequency and corresponding sea level pressure of anticyclones in the West Siberia and Mongolia Plateau are increased when the sea ice in the northern margin of the Eurasian continent is decreased,which verifies the effect of the less sea ice on the anticyclone activity.