Atmosphere Ocean Science Colloquium

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The disruption of the quasibiennial oscillation in 2016

Speaker: Peter Hitchcock, Cornell

Location: Warren Weaver Hall 1302

Date: Wednesday, April 22, 2020, 3:30 p.m.

Synopsis:

Equatorial winds in Earth's lower stratosphere exhibit a remarkably regular pattern of descending eastward and westward jets. Well-observed since the late 1950s, this 'quasibiennial oscillation' (QBO) is close to periodic with an average period near 28 months.  It is driven not by orbital eriodicities but by interactions between the zonal-mean jets and a spectrum of vertically propagating, equatorially-trapped waves. In the early months of 2016, this periodic evolution was disrupted: a shallow westward jet emerged in the core of a deeper eastward jet, in sharp contrast to the typical downward progression. This disruption can not be explained by the standard dynamical theory of the QBO. Reanalyses suggest that extratropical waves played a dominant role in generating the anomalous jet. In this talk I will discuss some of the mechanisms responsible for this disruption, arguing that the forcing by extratropical waves represents a strong feedback mechanism that should be predictable in advance. I'll argue further that this event, though singular, is highly valuable as a means to validate state-of-the-art models of the QBO.