On the Sensitivity of Annular Mode Dynamics to Stratospheric Radiative Time Scales

Abstract

Abstract Long decorrelation time scales of the annular mode are observed in the lower stratosphere. This study uses a simple dynamical model, which has been used extensively to study stratosphere–troposphere coupling to investigate the origin of the long dynamical time scales. Several long runs of the model are completed, with different imposed thermal damping time scales in the stratosphere. The dynamical time scales of the annular mode are found to be largely insensitive to the input thermal damping time scales, producing similar dynamical time scales in all cases below 50 hPa. This result suggests that the hypothesis that long time scales in the lower stratosphere are due to long radiative time scales in this region is false.