TY - JOUR
T1 - Anomalous dynamics of QBO disruptions explained by 1D theory with external triggering
AU - Match, Aaron
AU - Fueglistaler, Stephan
N1 - Publisher Copyright:
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PY - 2021/2
Y1 - 2021/2
N2 - The quasi-biennial oscillation (QBO) is an alternating, descending pattern of zonal winds in the tropical stratosphere with a period averaging 28 months. The QBO was disrupted in 2016, and arguably again in 2020, by the formation of an anomalous easterly shear zone, and unprecedented stagnation and ascent of shear zones aloft. Several mechanisms have been implicated in causing the 2016 disruption, most notably triggering by horizontal eddy momentum flux divergence, but also anomalous upwelling and wave stress. In this paper, the 1D theory of the QBO is used to show how seemingly disparate features of disruptions follow directly from the dynamics of the QBO response to triggering. The perturbed QBO is interpreted using a heuristic version of the 1D model, which establishes that 1) stagnation of shear zones aloft resulted from wave dissipation in the shear zone formed by the triggering, and 2) ascent of shear zones aloft resulted from climatological upwelling advecting the stagnant shear zones. Obstacles remain in the theory of triggering. In the 1D theory, the phasing of the triggering is key to determining the response, but the dependence on magnitude is less steep. Yet in MERRA-2, there are triggering events only 20% weaker than the 2016 triggering and equal to the 2020 triggering that did not lead to disruptions. Complicating matters further, MERRA-2 has record-large analysis tendencies during the 2016 disruption, reducing confidence in the resolved momentum budget.
AB - The quasi-biennial oscillation (QBO) is an alternating, descending pattern of zonal winds in the tropical stratosphere with a period averaging 28 months. The QBO was disrupted in 2016, and arguably again in 2020, by the formation of an anomalous easterly shear zone, and unprecedented stagnation and ascent of shear zones aloft. Several mechanisms have been implicated in causing the 2016 disruption, most notably triggering by horizontal eddy momentum flux divergence, but also anomalous upwelling and wave stress. In this paper, the 1D theory of the QBO is used to show how seemingly disparate features of disruptions follow directly from the dynamics of the QBO response to triggering. The perturbed QBO is interpreted using a heuristic version of the 1D model, which establishes that 1) stagnation of shear zones aloft resulted from wave dissipation in the shear zone formed by the triggering, and 2) ascent of shear zones aloft resulted from climatological upwelling advecting the stagnant shear zones. Obstacles remain in the theory of triggering. In the 1D theory, the phasing of the triggering is key to determining the response, but the dependence on magnitude is less steep. Yet in MERRA-2, there are triggering events only 20% weaker than the 2016 triggering and equal to the 2020 triggering that did not lead to disruptions. Complicating matters further, MERRA-2 has record-large analysis tendencies during the 2016 disruption, reducing confidence in the resolved momentum budget.
KW - Climate variability
KW - Quasibiennial oscillation
KW - Reanalysis data
KW - Stratosphere-troposphere coupling
KW - Stratospheric circulation
KW - Vertical motion
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U2 - 10.1175/JAS-D-20-0172.1
DO - 10.1175/JAS-D-20-0172.1
M3 - Article
AN - SCOPUS:85102183535
SN - 0022-4928
VL - 78
SP - 373
EP - 383
JO - Journal of the Atmospheric Sciences
JF - Journal of the Atmospheric Sciences
IS - 2
ER -