Periodicity disruption of a model quasi-biennial oscillation
Atmospheric and Oceanic Sciences Departmental Seminar Series
presents
Periodicity disruption of a model quasi-biennial oscillation
a talk by
Louis-Philippe Nadeau
ProfessorInstitut des sciences de la mer de Rimouski,
Université du Québec à Rimouski, Québec
The quasi-biennial oscillation (QBO) of equatorial winds on Earth is the clearest example of the spontaneous emergence of a periodic phenomenon in geophysical fluids. In recent years, observations have revealed intriguing disruptions of this regular behavior, and different QBO-like regimes have been reported in a variety of systems. The non-periodic nature of the reversals has been interpreted as the system's response to transient external variations. Here we show that part of the variability could be attributed to the intrinsic dynamics of wave-mean flow interactions in stratified fluids.
Using a constant-in-time monochromatic wave forcing, we explore the intrinsic variability of a hierarchy of simplified models of the QBO, ranging from a quasilinear model to fully nonlinear simulations. The existence of new bifurcations associated with faster and shallower flow reversals, as well as a quasiperiodic route to chaos are reported in these models.
Then, focusing on the regular QBO-like regime, we investigate how the proximity to a bifurcation point influences the resilience of a given oscillation to external variability by considering the effect of a time-dependent perturbation superimposed on its reference monochromatic wave forcing. We show that perturbations of the oscillation are widely amplified in the proximity of bifurcation points occurring in the phase space of these models, thus suggesting that intrinsic dynamics may be equally influential as external variability in explaining disruptions of this regular behavior.