  The polar vortices play a crucial role in the formation of the ozone hole and
can cause severe weather anomalies. Their boundaries, known as the vortex
`edges', are typically identified via methods that are either frame-dependent
or return non-material structures, and hence are unsuitable for assessing
material transport barriers. Using two-dimensional velocity data on isentropic
surfaces in the northern hemisphere, we show that elliptic Lagrangian Coherent
Structures (LCSs) identify the correct outermost material surface dividing the
coherent vortex core from the surrounding incoherent surf zone. Despite the
purely kinematic construction of LCSs, we find a remarkable contrast in
temperature and ozone concentration across the identified vortex boundary. We
also show that potential vorticity-based methods, despite their simplicity,
misidentify the correct extent of the vortex edge. Finally, exploiting the
shrinkage of the vortex at various isentropic levels, we observe a trend in the
magnitude of vertical motion inside the vortex which is consistent with
previous results.
