The Buffer Zone of the Quasi-Biennial Oscillation

The quasi-biennial oscillation (QBO) is a descending pattern of winds in the stratosphere that vanishes near the top of the tropical tropopause layer, even though the vertically propagating waves that drive the QBO are thought to originate in the troposphere several kilometers below. The region wher...

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Bibliographic Details
Published in:Journal of the atmospheric sciences 2019-11, Vol.76 (11), p.3553-3567
Main Authors: Match, Aaron, Fueglistaler, Stephan
Format: Article
Language:English
Subjects:
Acceleration
Angular momentum
Anomalies
Attenuation
Boundary conditions
Buffer zones
Cancellation
Coriolis force
Damping
Eddy momentum flux
Far fields
General circulation models
Gravitational waves
Momentum
Momentum flux
Momentum transfer
One dimensional models
Quasi-biennial oscillation
Standard deviation
Stratosphere
Torque
Tropical climate
Tropical tropopause
Tropopause
Troposphere
Wave propagation
Wind
Winds
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Summary:The quasi-biennial oscillation (QBO) is a descending pattern of winds in the stratosphere that vanishes near the top of the tropical tropopause layer, even though the vertically propagating waves that drive the QBO are thought to originate in the troposphere several kilometers below. The region where there is low QBO power despite sufficient vertically propagating wave activity to drive a QBO is known as the buffer zone. Classical one-dimensional models of the QBO are ill suited to represent buffer zone dynamics because they enforce the attenuation of the QBO via a zero-wind lower boundary condition. The formation of the buffer zone is investigated by analyzing momentum budgets in the reanalyses MERRA-2 and ERA-Interim. The buffer zone must be formed by weak wave-driven acceleration and/or cancellation of the wave-driven acceleration. This paper shows that in MERRA-2 weak wave-driven acceleration is insufficient to form the buffer zone, so cancellation of the wave-driven acceleration must play a role. The cancellation results from damping of angular momentum anomalies, primarily due to horizontal mean and horizontal eddy momentum flux divergence, with secondary contributions from the Coriolis torque and vertical mean momentum flux divergence. The importance of the damping terms highlights the role of the buffer zone as the mediator of angular momentum exchange between the QBO domain and the far field. Some far-field angular momentum anomalies reach the solid Earth, leading to the well-documented lagged correlation between the QBO and the length of day.
ISSN:0022-4928
1520-0469
DOI:10.1175/JAS-D-19-0151.1