Atmosphere Ocean Science Colloquium
The disruption of the quasibiennial oscillation
Speaker: Peter Hitchcock, Cornell
Date: Wednesday, November 18, 2020, 3:30 p.m.
The winds in Earth's tropical lower stratosphere exhibit a series of alternating eastward and westward jets that form near 35 km above the surface, descending to about 18km, just above the tropical tropopause. This 'quasibiennial oscillation,' apparent in equatorial weather balloon observations since the late 1950s, has a remarkably regular period near 28 months. This is notably distinct from any orbital periodicities, and is understood to arise as a result of non-linear interactions between upward propagating atmospheric waves and the jets themselves.
In early 2016, the quasibiennial oscillation was disrupted by a shallow westward jet that emerged near 40 hPa within a relatively deep eastward phase of the standard oscillation. This disruption was unprecedented in the observational record.
In this talk I will discuss a series of integrations of the dry primitive equations that also exhibit disruptions of a deep layer of equatorial eastward winds by shallow a westward jet. Like the observed disruption, but in contrast to the standard mechanism, the disruptions in this idealized model are driven by extratropical waves impinging horizontally on the core of the equatorial westerly winds.
These numerical experiments point to a strong positive feedback mechanism that was likely responsible for the observed disruption. They further suggest that the disruption should have been predictable several months in advance.