Tropopause folds are one of the key mechanisms of stratosphere–troposphere exchange(STE) in extratropical regions,transporting ozone-rich stratospheric air into the middle and lower troposphere. Although there have been many studies of tropopause folds that have occurred over Europe and North America,a very limited amount of work has been carried out over northeastern Asia. Ozonesondes produced by the Institute of Atmospheric Physics were launched in Changchun(43.9?N,125.2?E),Northeast China,in June 2013,and observed an ozone-enriched layer with thickness of 3 km and an ozone peak of180 ppbv at 6 km in the troposphere. The circulation field from the European Centre for Medium-Range Weather Forecasts Interim Reanalysis(ERA-Interim) dataset shows that this ozone peak was caused by a tropopause fold associated with a jet stream at the eastern flank of the East Asian trough. By analyzing the ozone data from the ozone monitoring instrument and Weather Research and Forecasting model with Chemistry(WRF-Chem) simulations,it was found that a high ozone concentration tongue originating from the lower stratosphere at high latitude(near central Siberia) intruded into the middle troposphere over Changchun between 5 and 8 km on 12 June 2013. The high-resolution WRF-Chem simulation was capable of describing events such as the tropopause fold that occurred on the cyclonic shear side of the jet stream. In addition,the TRAJ3 D trajectory model was used to trace the origin of measured secondary ozone peaks in the middle troposphere back,for example,to stratospheric intrusion through the tropopause fold.
European Centre for Medium-Range Weather Forecasts Re-Analysis Interim(ERA-Interim)reanalysis data and satellite data,and trajectory model were applied to analyze the dynamical,thermo-dynamical,and chemical structure in the upper troposphere and lower stratosphere(UTLS)of an intense cut-off low(COL)event occurring over East Asia during June 19-23,2010,and to characterize the process and transport pathway of deep stratospheric intrusion.The Atmospheric Infrared Sounder(AIRS)ozone data and the Global Positioning System Ozone(GPSO3)sonde data showed that the air mass originating from the polar formed a region with relatively high values of potential vorticity(PV)and ozone in the center of COL,and a secondary ozone peak appeared in the upper troposphere during mature stage of the COL.Forward trajectory simulation suggested that during the first stage of COL,deep stratospheric intrusion associated with strong northerly wind jet on the west side of the upper-level trough transported ozone-rich air from the polar lower stratosphere into the middle and lower troposphere in the mid-latitude,and increased the ozone concentration there.During the mature stage of the COL,stratospheric air was transported counterclockwise into the troposphere.Backward trajectory model was used to find the source regions of air mass within the COL during its mature stage.Model results show that air masses with high ozone concentration in the center of the COL have two source regions:one is the subpolar vortex which lies in northern part of Center Siberia,where ozone-rich air plays a major role in increasing the ozone concentrations,and the other is the strong shear region which is near by the cyclonic side of the extratropical jet axis(west of 90°E,near 50°N).The air masses with low ozone concentration around the COL also have two source regions:one is the anticyclonic side of the extratropical jet axis,where the air mass with the relatively low ozone concentration at the bottom of the COL is mainly controlled by horizontal movement,and the
