The Vertical Structure of Annular Modes

Stratosphere–troposphere interactions are conventionally characterized using the first empirical orthogonal function (EOF) of fields such as zonal-mean zonal wind. Perpetual-winter integrations of an idealized model are used to contrast the vertical structures of EOFs with those of principal oscilla...

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Bibliographic Details
Published in:Journal of the atmospheric sciences 2018-10, Vol.75 (10), p.3507-3519
Main Authors: Sheshadri, Aditi, Plumb, R. Alan, Lindgren, Erik A., Domeisen, Daniela I. V.
Format: Article
Language:English
Subjects:
Anomalies
Climate
Dynamical systems
Empirical analysis
Equilibrium
Evolution
Modes
Northern Hemisphere
Orthogonal functions
Propagation modes
Stratosphere
Structures
Topography
Troposphere
Variability
Vertical profiles
Weighting
Wind
Zonal flow
Zonal flow (meteorology)
Zonal winds
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Summary:Stratosphere–troposphere interactions are conventionally characterized using the first empirical orthogonal function (EOF) of fields such as zonal-mean zonal wind. Perpetual-winter integrations of an idealized model are used to contrast the vertical structures of EOFs with those of principal oscillation patterns (POPs; the modes of a linearized system governing the evolution of zonal flow anomalies). POP structures are shown to be insensitive to pressure weighting of the time series of interest, a factor that is particularly important for a deep system such as the stratosphere and troposphere. In contrast, EOFs change from being dominated by tropospheric variability with pressure weighting to being dominated by stratospheric variability without it. The analysis reveals separate tropospheric and stratospheric modes in model integrations that are set up to resemble midwinter variability of the troposphere and stratosphere in both hemispheres. Movies illustrating the time evolution of POP structures show the existence of a fast, propagating tropospheric mode in both integrations, and a pulsing stratospheric mode with a tropospheric extension in the Northern Hemisphere–like integration.
ISSN:0022-4928
1520-0469
DOI:10.1175/JAS-D-17-0399.1