Stratospheric Vacillations in a General Circulation Model

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Abstract
The variability in the Northern Hemisphere winter stratosphere is studied with a general circulation model run in perpetual January mode. The variability is of oscillatory nature with a timescale of approximately 100 days. Warmings appear in the upper stratosphere and descend through the stratosphere until they dissipate close to the tropopause. Warming of the upper stratosphere is accompanied by cooling of the lower stratosphere and vice versa. Experiments with time-independent tropospheres show that the vacillations originate from a stratospheric instability when driven by a constant wave forcing at the tropopause. The general circulation model experiments are discussed in the light of low-dimensional models. Abstract The variability in the Northern Hemisphere winter stratosphere is studied with a general circulation model run in perpetual January mode. The variability is of oscillatory nature with a timescale of approximately 100 days. Warmings appear in the upper stratosphere and descend through the stratosphere until they dissipate close to the tropopause. Warming of the upper stratosphere is accompanied by cooling of the lower stratosphere and vice versa. Experiments with time-independent tropospheres show that the vacillations originate from a stratospheric instability when driven by a constant wave forcing at the tropopause. The general circulation model experiments are discussed in the light of low-dimensional models.