Stratosphere–troposphere coupling in the lead-up to stratospheric sudden warmings

The stratosphere and the troposphere exhibit a strong coupling during the Northern Hemisphere winter season. This coupling is particularly strong during the formation of large stratospheric wind and temperature anomalies (major or minor warmings), which may be accompanied by tropospheric flow anomalies.

Planetary Rossby waves account for the main part of the large-scale vertical coupling in the extratropical atmosphere. Several studies have found strong wave-1 amplitude anomalies at and below the stratospheric polar vortex prior to stratospheric sudden warmings. We have found a similar wave-1 signal prior to sudden warmings in a spectral core model where only wave-2 is explicitly forced. This suggests a pre-conditioning of the vortex prior to the warmings, or even an evolution into a state that favors sudden warmings.

This paper explores the role of the mutual coupling between the troposphere and the stratosphere for sudden as well as final warmings. This is done by employing a general circulation model of intermediate complexity (a spectral core model) for model stratospheric variability in the form of sudden as well as final warmings.