How might the stratosphere influence the troposphere?

Abstract

Recent observational studies suggest that the strength of the wintertime stratospheric polar vortex influences the subsequent tropospheric circulation, specifically the state of the Arctic oscillation (AO).  Here, dynamical mechanisms that can explain these observations are explored.   Key observations are, first, that the AO is a robust eddy-driven mode of tropospheric variability, found in models lacking a well resolved stratosphere, and in observations in seasons when the troposphere and stratosphere are effectively uncoupled; secondly, that the meridional scale of the variations in the troposphere is significantly smaller than that of stratospheric variations in the polar vortex.

Based on these considerations, we propose a mechanism in which anomalous stratospheric wave driving, through "downward control" weakly forces the AO.  This forcing is reinforced in the troposphere by interactions with transient eddies.  The mechanism is demonstrated in two idealized models.