Analysis of the Dynamical Forcing of Persistent Anomaly Life Cycles in a General Circulation Model

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Investigations of persistent atmospheric flow anomalies have found that high frequency transient eddies play an important role in maintaining anomalies against downstream propagation. The precise way in which these transient eddies affect the onset and decay of the anomalous patterns remains a question. For example, the onset of anomalies is often associated the upstream intensification of synoptic-scale disturbance )storms), but it is not clear whether this intensification occurs in a background environment neutral or stable with respect to large-scale eddies or as a consequence of large-scale instability. A diagnostic technique has been developed that allows examination of the forcing of the slowly-varying large-scale flow in terms of both low frequency and high-frequency transient eddy processes. It has been applied to perpetual January data from a two level general circulation model. Results indicate that the low frequency processes typically, thought not always, determine the local growth or decay of anomalies. Under this award, the principal investigators will apply this diagnostic technique to the output form a sophisticated model, the Community Climate Model of the National Center for Atmospheric Research, and compare the results with those of the previous study. This research will enhance our understanding of the causes of intraseasonal climate variability.