Atmosphere Ocean Science Colloquium

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The Unified Internal Dynamics and Global Interactions of the Quasi-Biennial Oscillation

Speaker: Aaron Match, NYU

Location: Warren Weaver Hall 1302

Date: Wednesday, March 2, 2022, 3:30 p.m.

Synopsis:

Tropical stratospheric dynamics are dominated by the Quasi-Biennial Oscillation (QBO), an alternating, descending pattern of zonal winds with a period averaging 28 months. Although the QBO is driven by dissipation of vertically propagating atmospheric waves, the QBO vanishes several kilometers above the wave source, forming a buffer zone. Foundational 1D model experiments suggested that the buffer zone forms where tropical stratospheric upwelling opposes the descent of the QBO, and this upwelling hypothesis has been invoked to attribute global warming-induced weakening of the QBO in the buffer zone region. Today’s talk overturns the upwelling hypothesis by revealing that the foundational model experiments were logically circular, having prescribed the buffer zone through the boundary conditions. The only general way to form a buffer zone in the classical QBO model is to damp QBO angular momentum towards zero. Atmospheric reanalyses show evidence of such damping, resulting from horizontal momentum flux divergence, which exports QBO angular momentum anomalies outside the QBO region. Revisiting the question of attributable trends, the impacts of global warming on QBO amplitude will be shown to be modest and consistent with a vertical shift in QBO amplitudes as the troposphere expands. Lastly, puzzling features of the QBO disruptions of 2016 and 2020 will be explained as simple consequences of the internal dynamics of the QBO in response to the well-documented planetary wave incursion into the QBO region.