The Dynamics of Weather Regime Transitions

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A pressing problem in efforts to improve numerical extended range weather forecasts is to better predict the establishment and breakdown of persistent weather regimes. While much effort has been devoted to studying the maintenance of these regimes, less is known about their life cycles. The principal investigator will conduct a comprehensive diagnostic study of weather regime transitions in version 2 of the Community Climate Model (CCM) of the National Center for Atmospheric Research. Specifically, the PI will attempt to identify the dynamical and physical mechanisms responsible for regime transitions in the midlatitudes. The first task will be to validate the statistics, structure and time evolution of persistent large-scale flow anomalies occurring in extended integrations of the CCM2. Characteristics of the simulated events then will be compared with observational analyses. Using model "data" allows the PI to avoid the problems inherent in observational studies as nonconservative processes and secondary circulations which are known explicitly in the model and there are no difficulties with sparse or uncertain observations. ***