# Uncovering the Edge of the Polar Vortex

## TL;DR

This paper demonstrates that elliptic Lagrangian Coherent Structures effectively identify the material boundary of the polar vortex, outperforming traditional methods and revealing significant temperature and ozone concentration contrasts.

## Contribution

It introduces the use of elliptic LCSs for accurately delineating the polar vortex boundary as a material surface, improving upon existing frame-dependent and non-material approaches.

## Key findings

- Elliptic LCSs correctly identify the vortex's outermost material boundary.
- Temperature and ozone concentration show significant contrast across the identified boundary.
- Potential vorticity methods often misidentify the vortex extent.

## Abstract

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.