9628850 Robinson This award provides support for Dr. Robinson's continuing research on the low frequency variability of the extratropical atmosphere and employs a mix of observational analyses, analyses of general circulation model output, and simple numerical models. The principal investigator will focus on three tasks. The first is the development and application of a generalized barotropic model to be used for diagnostic and process studies of low frequency variability, both observed and in general circulation models (GCMs). This is a new undertaking by the PI and involves a new, creative approach that employs the PI's empirically derived formulation of the relationship between potential vorticity and the streamfunction. The other two tasks represent continuations of previously supported work. One is a series of diagnostic studies of the dynamics governing the zonal index in GCM output and in observations, and of the predictability of the zonal index. The other major area involves analytical studies of the nonlinear behavior of the barotropic instability of zonally asymmetric basic states which is believed to contribute to the low frequency variability in the atmosphere. All of these studies are important for advancing understanding of atmospheric dynamic processes that are critical to improved extended range prediction. ***
