Surface impacts from variations in the Arctic stratospheric polar vortex
Thomas Reichler (Department of Atmospheric Sciences, University of Utah, Salt Lake City, USA)
Thomas Reichler travaille au Department of Atmospheric Sciences, University of Utah, Salt Lake City. USA)
The stratospheric circulation influences the surface weather and climate in many ways. Prominent examples are variations in the Brewer-Dobson circulation, the quasi-biennial oscillation, and the stratospheric polar vortex. In this talk, I explore the surface impacts from natural variations in the strength of the Arctic stratospheric polar vortex. The polar vortex is modulated by vertically propagating planetary waves, sometimes leading to rapid changes. The changes create surface signals that can be used to enhance the sub-seasonal to seasonal predictability.
Much of the past research on polar vortex variations was focused on so-called “sudden stratospheric warmings” (SSWs), episodic events in which the polar vortex winds completely break down and the polar stratosphere warms. Here, I show that a focus on SSWs is somewhat too narrow. There exists a range of other polar vortex events, which also create important surface signals, but which are not classified as SSWs. I propose an alternative more comprehensive definition that captures a wider range of polar vortex events.
The definition is based on the time-integrated anomalous planetary wave activity flux, which typically propagates upward from the troposphere into the lower stratosphere a few days before the polar vortex events. I use reanalysis data and a long climate model simulation to investigate the detailed evolution of the new events and to demonstrate their usefulness in the context of surface predictability.
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