Competing Theoretical Frameworks for Atmospheric Variability: Quasi-geostrophic Turbulence vs Linear Stochastic Dynamics

Saturday, September 29, 2001 - 9:30am - 10:30am
Keller 3-180
Joseph Tribbia (National Center for Atmospheric Research)
Up until recently, the standard explanation of atmospheric patterns of variability relied upon the dynamical systems paradigm of successive bifurcations from laminar stationary states, to periodic motions, to low order chaos and on to high dimensional, (quasi-geostrophic) turbulence. This view can be applied both to medium scale weather fluctuations and planetary scale low frequency anomalies. The latter can also be viewed, however, from the perspective of planetary scales induced by the nonlinear organization of medium scale fluctuations.

Recently this view has been challenged and an alternative explanation has been seriously proposed in which all transient atmospheric patterns-from weather to planetary scale-are the result of random forcing. The background state upon which this transient motion is excited is the laminar stationary background obtained in the bifurcation paradigm, but this flow is never linearly unstable. Thus no bifurcation actually occurs. My talk will pursue a determination from models and observations as to which paradigm best fits atmospheric variability.