Geodesic vortex detection on curved surfaces: Analyzing the 2002 austral stratospheric polar vortex warming event

TL;DR

This paper extends geodesic vortex detection methods to curved surfaces and applies it to analyze the 2002 austral stratospheric polar vortex warming event, providing detailed lifecycle and ozone depletion insights.

Contribution

The authors adapt geodesic vortex detection to Riemannian manifolds and develop a birth-and-death vortex algorithm for 3D flows, enabling detailed vortex analysis on curved surfaces.

Findings

Identified the vortex's birth, splitting, and death phases.

Provided new kinematic insights into ozone depletion within the vortex.

Extended vortex detection techniques to curved surfaces and 3D flows.

Abstract

Geodesic vortex detection is a tool in nonlinear dynamical systems to objectively identify transient vortices with flow-invariant boundaries that defy the typical deformation found in 2-d turbulence. Initially formulated for flows on the Euclidean plane with Cartesian coordinates, we have extended this technique to flows on 2-d Riemannian manifolds with arbitrary coordinates. This extension required the further formulation of the concept of objectivity on manifolds. Moreover, a recently proposed birth-and-death vortex framing algorithm, based on geodesic detection, has been adapted to address the limited temporal validity of 2-d motion in otherwise 3-d flows, like those found in the Earth's stratosphere. With these adaptations, we focused on the Lagrangian, i.e., kinematic, aspects of the austral stratospheric polar vortex during the exceptional sudden warming event of 2002, which resulted in the vortex splitting. This study involved applying geodesic vortex detection to isentropic winds from reanalysis data. We provide a detailed analysis of the vortex's life cycle, covering its birth, the splitting process, and its eventual death. In addition, we offer new kinematic insights into ozone depletion within the vortex.