On the seasonal structure of the Arctic Stratospheric Oscillation

Abstract

This study examines the seasonal characteristics of the inter-annual stratospheric variability that impact the polar tropospheric climate in the northern hemisphere winter, herein referred to as the Arctic Stratospheric Oscillation (ASO). The westerly wind anomalies associated with the ASO begin in the middle stratosphere around 60°N in early winter, gradually strengthen to reach their maximum in the upper stratosphere in January, and then move downwards with a decrease in intensity to the lower stratosphere in March. The seasonal progression of the ASO is found to be associated with increasing negative sea level pressure anomalies at the polar cap, reaching their maximum in March. It has been determined that the main driving force for ASO is planetary waves, with a major contribution from non-stationary waves. It is suggested that the ASO could have an impact on the occurrence of Sudden Stratospheric Warmings and Vortex Intensifications until midwinter. November signal of the ASO is found to be a promising candidate for predicting the polar climate for the subsequent winter season in both the troposphere and the stratosphere.