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In this study, energy spectrum and energy flow of the large-scale atmospheric motions are examined in reference to the Arctic Oscillation index. Attention is concentrated to the barotropic component of the atmosphere in the framework of the 3D normal mode decomposition.According to the result of the observational analysis in the phase speed domain, the Arctic Oscillation (AO) is characterized as the energy increase at the meridional index l=3 with simultaneous decrease at l=5 of the zonal field. The result is consistent with the theory of the AO by the singular eigenmode of the global atmosphere. The accumulation of energy at the eigenmode of the AO is explained by the enhanced energy flux FZi associated with the zonal-wave interaction.It is found in this study that the energy flux FZi comes from eddies at the spherical Rhines speed cR where the planetary-scale Rossby wave becomes stationary. The result suggests that the low-frequency variability associated with the AO is maintained by energy flux from cR, which is compensated by the up-scale energy cascade from synoptic eddies in addition to the forced stationary planetary waves by topography.

Energy Spectrum and Energy Flow of the Arctic Oscillation in the Phase Speed Domain