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The Buffer Zone of the Quasi-Biennial Oscillation

Author(s): Match, Aaron; Fueglistaler, Stephan

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Abstract: 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.
Electronic Publication Date: 5-Nov-2019
Citation: Match, Aaron, and Stephan Fueglistaler. "The buffer zone of the quasi-biennial oscillation." Journal of the Atmospheric Sciences 76, no. 11 (2019): 3553-3567. DOI: 10.1175/JAS-D-19-0151.1.
DOI: doi:10.1175/JAS-D-19-0151.1
ISSN: 0022-4928
EISSN: 1520-0469
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Pages: 3553 - 3567
Type of Material: Journal Article
Journal/Proceeding Title: Journal of the Atmospheric Sciences
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.
Notes: Related Item includes supplemental figures.

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