"Stratospheric variability and tropospheric climate change"

Variability of the polar stratospheric vortex impacts weather and climate patterns at the Earth’s surface on timescales from weeks to decades. In this talk, I will discuss the processes that set polar vortex variability on interannual, seasonal, and decadal timescales, as well as the dynamics of tropospheric mid-latitude jet stream and storm track responses to perturbations from the stratosphere (and, indeed, to external forcing in general, such as rising concentrations of greenhouse gases).

I will introduce an idealized, dynamically comprehensive atmospheric model that captures the observed behavior of the Arctic and Antarctic polar vortices, and demonstrate seasonal effects of stratospheric variability on surface wind and precipitation patterns. I will then use the dynamics of tropospheric responses to this variability as a demonstration of a more general principle – that of the link between natural variability of the climate system on the one hand and its response to forcing on the other. I will use a fluctuation-dissipation theorem formulation to show the existence of propagating eigenmodes of the atmosphere, describing systematic poleward migration of wind anomalies, and discuss some of the implications of these propagating modes in climate prediction. [Background reading: 1 2 3]