Stratospheric Forcing of Surface Climate in the Arctic Oscillation

Abstract

Diagnostic results are presented indicating that during the Arctic oscillation surface climate variations are directly forced by changes in the strength of the stratospheric polar vortex. To be specific, large-scale potential vorticity anomalies in the lower stratosphere induce zonally symmetric zonal wind perturbations extending downward to the earth's surface. This represents a large-scale annular stirring of the troposphere from above. During discrete events, this influence is manifested as a downward transient pulse initially emanating from the midstratosphere and ultimately altering surface weather. It is suggested that this mechanism may help to explain several observed stratospheric influences upon surface climate, including the effects of volcanic eruptions, the solar cycle, ozone depletion, and greenhouse gases.