Three-dimensional dynamic features of two arctic oscillation types

Abstract

We investigated the differences between stratospheric (S-type) and tropospheric (T-type) Arctic Oscillation (AO) events on the intraseasonal time scale, in terms of their influences on surface air temperature (SAT) over the Northern Hemisphere and the dynamic features associated with their spatial structures. S-type AO events showed a stratosphere-troposphere coupled structure, while T-type events exhibited a stratosphere-troposphere uncoupled structure. The annular SAT anomalies over the Northern Hemisphere were found to be associated with S-type AO events, whereas such an annular feature was substantially destructed in T-type AO events. The different horizontal structures in the troposphere of the two types could mainly be attributed to transient eddy feedback forcing. As for the vertically uncoupled structure of Ttype events, the underlying dynamical features that differentiate them from S-type events lie in the vertical propagation of zonally confined Rossby waves. In T-type events, the zonally confined Rossby wave packets can emanate from the significant height anomalies over Northeast Asia, where one vertical waveguide exists, and then propagate upward into the stratosphere. In contrast, such a vertical propagation was not evident for S-type events. The stratospheric anomalies associated with the upward injection of the zonally confined Rossby waves from the troposphere in T-type events can further induce the anomalous vertical propagation of planetary waves (PWs) through the interference between the climatological-mean PWs and anomalous PWs, leading to the final stratosphere-troposphere uncoupled structure of T-type events.