Climatic Effects And Formation Mechanism Of Interannual Variation Of The Northeast Low Vortex During Spring And Summer

This paper based on the data 6-hourly 850 h Pa geopotential height field from ERA-Interim 1979-2013,and uses the 2D cyclone area objective identification method which based on the outermost enclosed of cyclones that recognizing the cyclones those affect northeast China.And analysis cyclone characteristics differ in different seasons.We choose the spring and summer seasons when the cyclones most active as the research periods,the 35-year northeast low vortex intensity index in spring and summer seasons are redefined.The activity routines,climate influences,the characteristics of circulation background in abnormal activity years and formation mechanisms of vortex activity.The results show that:(1)The 2D cyclone area objective identification method has a better expression ability to describe cyclones in East Asia.From 1979-2013,the activities of the Northeast cyclones in different seasons were significantly different.It occurs more frequently in spring and summer,and the proportion of cyclones with short life cyclones(<72h)is larger than that with longer life cyclones(72-180h).According to the classification of moving distance,large-scale(> 2000km)cyclones occur the most in spring,and medium(500-2000km)and small(<500km)scale cyclones occur the most in summer.According to the classification of life cycle,the eddy kinetic energy distribution of the cyclones in longer life cycle(1-6d)is roughly consistent with those of shorter life cycle(<1d),but its intensity is much greater than that of short life cycle.According to the classification of cyclone diameters,the average vorticity of cyclones of the weather scale and cyclones on the sub-weather scale is the largest in summer,spring is smaller than summer.(2)During the spring of 1979-2013,the northeast low vortex's activity was mainly interannual.The enhancement of the northeast low vortex anomaly in spring will cause a significant increase in local precipitation and China's significant warming except Northeast,Tibet and other places.In the strong years in spring,there was a relatively uniform distribution situation among the geopotential height field,wind field and temperature field,and forming a favorable configuration.The early snow cover has animportant effect on the ground radiation flux,and the snow cover in the northeast region has decreased significantly.The downstream propagation of Rossby waves induced by the heated gas column and strengthen the cyclonic circulation in the northeast.Finally,numerical experiments reproduced the main modal and abnormal changes under the previous snow cover forcing.(3)In the summer of 1979-2013,the northeast low vortex activity was dominated by interannual changes,and its activity was significantly positively related to precipitation in the northeast region,which was contrary to the abnormal changes in local temperature.The geopotential height field,wind field,and temperature field have corresponding distributions.There is a significant positive correlation between the sea surface temperature in the Newfoundland Basin-Western Europe Basin area and the intensity of low-vortex activity in the Northeast in summer.When the sea temperature in the Newfoundland Basin-Western Europe Basin area increased during the summer,the Northeast low vortex activity increased during the same period.Conversely,when the sea temperature was low,the Northeast low vortex activity also weakened.