Trace Material Exchange In The UTLS Region During Cut-off Low Systems Over Northeast Asia

This paper is based on the background of stratosphere-troposphere exchange,focusing on the stratosphere-troposphere exchange process caused by COLs,and screening statistics on COL cases occurring in Northeast Asia from 2005 to 2015.Using ERA-Interim high-resolution data and AIRS satellite data,the temporal and spatial distribution characteristics of the selected COLs internal substances(ozone,water vapor)were statistically analyzed,and the UTLS regional material distribution characteristics and overall effects caused by COLs were examined.The FLEXPART-WRF trajectory transport model is further used to simulate the trajectory and source of the air mass.The simulation results are used to analyze the multi-time scale exchange process and possible reasons for the distribution of the material based on the statistics of the observed data.The main conclusions are as follows:1.A total of 186 cases of COLs occurred in Northeast Asia from 2005 to 2015 were screened using automatic identification methods,of which 155 were "deep" and 31 were"shallow".155 "deep" COLs were divided into 71 strong COLs and 84 weak COLs.2.By using ERA-Interim reanalysis data and AIRS satellite data on 186 statistical analysis of COLs,we can see that at the strongest time of COLs,the reduction of water vapor content and the increase of ozone concentration in the upper troposphere(300 hPa)are related to the dynamics of high-level jets and the reduction of tropospheric tops.The distribution of water vapor and ozone in the mid-troposphere(500 hPa)is related to the system's own horizontal circulation.The range of high ozone concentration and ozone content in UTLS caused by COL is related to the strength of the system itself.3.Simulation results for the typical case of June 2010 through the FLEXPART-WRF trajectory delivery model show that the motion(delivery)of the air mass presents multiple time-scale processes:The air mass can be divided into three stages in the process of invading from the lower stratosphere to the middle of the troposphere according to the change of its height with time.The first stage was slow subsidence.The air mass dropped about 921.0 m within 36 h.The second stage is the rapid invasion stage.The air mass descends vertically at a height of about 2061.6 m within 36 h;the third stage is the relatively slow subsidence stage,and the air mass droped about 1095.3 m within 26 h.This movement process is consistent with the material distribution characteristics obtained from observation data.At 300 hPa and 500 hPa,the air masses in the COLs mainly originate from the polar vortex over the middle Siberia,near the temperate jet axis,and in the low trough on the south side of the COLs.