Abstract

The present paper examines the northern stratosphere during April 2020, when the polar vortex split into two cyclonic vortices after a winter with the strongest ozone depletion on record. We examine the dynamical evolution that led to the split at middle and lower stratospheric levels and the distribution of ozone between the main and off-spring vortices. Finally, we look at the vertical structure of the split down to the troposphere. The split event is analyzed with Lagrangian tools and an Eulerian diagnostic of planetary wave activity. The findings confirm the key role for the split played by a flow configuration with a polar hyperbolic trajectory and associated manifolds. A trajectory analysis illustrates how the ozone distribution between vortices was such that ozone poor air remained in the main vortex. The off-spring vortex became part of a deep structure from the troposphere, and connections with tropospheric disturbances over Eurasia are suggested.