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| Two Types of Arctic Oscillation and Their Associated Dynamic Features |
| SHI Ning,BUEH Cholaw |
| 1. Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; 2. Climate Change Research Center, Chinese Academy of Sciences, Beijing 100029, China;3. International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China |
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Abstract In this paper, the dynamical evolutions of two types of Arctic Oscillation (AO), the stratospheric (S) and tropospheric (T) types, have been investigated on an intermediate time scale in terms of transient eddy feedback forcing and three-dimensional Rossby wave propagation. S-Type (T-type) events are characterized by an anomalous stratospheric polar vortex that is in phase (out of phase) with its tropospheric counterpart. Approximately one- third of AO events, both positive and negative, are T-type events. For the positive phase of a T-type event, the formation and maintenance of stratospheric positive anomalies over the polar cap are associated with an upward propagation of Rossby wave packets originating from the near-tropopause altitude over northeastern Asia. However, such upward propagating features are not found for S-type events. In the troposphere, transient eddy feedback forcing is primarily responsible for the meridional seesaw structure of both the S- and T-type events, with an additional contribution from Rossby wave propagation.
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Received: 23 June 2011
Revised: 19 July 2011
Accepted: 31 July 2011
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