Predictability and Maintenance of Variance in Atmospheric Flows

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9623539 Farrell The award continues support for research aimed at developing a general stability theory for atmospheric flows as well as a theory for the dynamics of turbulence in strongly sheared flows such as the midlatitude jet. The principal investigator will pursue these goals using a combination of theoretical models and analysis of simulations with a general circulation model (GCM). The project involves two major thrusts. The first builds on theoretical work completed under the last award. The aim is to determine the variance and fluxes maintained by stochastic forcing of a GCM with realistic zonally varying jet structure and to compare these variances and fluxes with those obtained from the statistical means of a long time integration of the GCM. A version of NCAR's Community Climate Model (CCM2) will be used. It is hoped that this study will shed light on the dynamics responsible for producing localization of storms in particular regions and the sensitivity of storm tracks to alteration. The project will be done in collaboration with an NCAR scientist. The second research focus involves a more theoretically focused and generalized study of the underlying operator in turbulent model systems and GCMs and its stability properties. An additional topic will be undertaken if time permits. This study will examine the stability of time dependent flows - specifically, the relationship between transient growth of perturbations to the time mean flow and the emergence of the first Lyapunov mode and the role of non-normality in supporting both the short time error growth and the asymptotic Lyapunov modes. ***