Generation of low particle numbers at the edge of the polar vortex

The Antarctic vortex plays a well-known role in stratospheric ozone depletion in the early southern spring. One key requirement for this phenomenon is the isolation of air from inside the vortex to that from mid-latitudes. This paper seeks a new way to present this separation leading to isolation process by integrating several Lagrangian methods: a flow following coordinate system that combines a contour advection technique, a Lagrangian particle model, and a vortex diagnostic method, with new ways of contour particle initializations, visualization, and interpretations. We found that there exists a distinctive area with low density of contour particle numbers in the vortex edge region, and this low particle density region separates high particle density areas inside the vortex from those in mid-latitudes. We demonstrated the existence of an area with low particle numbers surrounded by the high particle numbers to the north (inside the vortex) and to the south (mid-latitudes). We show that the polar night jet is (1) efficient in generating this low particle density plateau that separate particles from inside the vortex to that from outside the vortex. (2) The polar night jet can pull particles from outside the vortex to the vortex edge region, and maintaining these particles in the polar night jet and carrying them around the polar vortex. Hence, the existence of a proper polar night jet is the key process in separating particles from inside the vortex to those from mid-latitudes, and the meridional profile of zonal winds and their time-varying behaviour directly affect the distribution of particles both inside the vortex and at mid-latitudes.