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Understanding the mechanisms for tropical surface impacts of the quasi-biennial oscillation (QBO)
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  • Jorge Luis Garcia-Franco,
  • Lesley J Gray,
  • Scott M. Osprey,
  • Robin Chadwick,
  • Jonathan Lin
Jorge Luis Garcia-Franco
Lamont-Doherty Earth Observatory, Columbia University, New York, University of Oxford

Corresponding Author:jlg2280@columbia.edu

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Lesley J Gray
NCAS-Climate, Department of Physics, Oxford University
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Scott M. Osprey
NCAS-Climate, Department of Physics, Oxford University
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Robin Chadwick
Met Office
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Jonathan Lin
Lamont-Doherty Earth Observatory, Columbia University, New York
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This study evaluates the main hypotheses to explain a coupling between the quasi-biennial oscillation (QBO) in the tropical stratosphere and the tropical troposphere and surface. The impact of the QBO on tropical convection and precipitation is investigated through nudging experiments using the UK Met Office Hadley Centre Unified Model (UM). The model control simulations show robust links between the internally generated QBO and tropical precipitation and circulation. The model zonal wind in the tropical stratosphere was nudged above 90 hPa in atmosphere-only and coupled ocean-atmosphere configurations. The simulation of convection and precipitation in the atmosphere-only simulations is not statistically significantly different between the experiments with and without nudging, which may indicate that SST-convection coupling is needed for any QBO influence on the tropical lower troposphere and surface. In the coupled experiments, the precipitation and SST relationships with the QBO phase disappear when nudging is applied. Evidence from the nudging experiments shows that the QBO influence over lower stratospheric static stability is not sufficient to produce tropical surface impacts. The nudging also reduced the influence of the lower troposphere to the upper branch of the Walker circulation, irrespective of the QBO, indicating that the upper troposphere has been slightly decoupled from the surface by the nudging. These results suggest that nudging all grid-points might mute relevant feedback processes, including high cloud radiative effects and wave mean flow interactions, occurring at the tropopause level.
13 Jan 2023Submitted to ESS Open Archive
17 Jan 2023Published in ESS Open Archive