Persistent anomaly forcing in a two-level global circulation model
- Environment Dynamics Research, Inc., Miami, FL (United States)
Perpetual January data from a simple global two-level model are used to diagnose forcing of the model's low-frequency (LF), large-scale flow. The forcing is considered within the context of a hypothetical low-order model that resolves only slowly varying planetary-scale modes. The forcing is partitioned into resolved components consisting of LF, planetary-scale processes and unresolved components that involve high-frequency (HF) transient eddy and LF synoptic-scale effects. Spatial patterns of the net tendencies of low-pass filtered, planetary-scale barotropic streamfunction and vertically averaged temperature are compared with corresponding patterns of resolved and unresolved forcing during the onset, maintenance, and decay stages of composited persistent anomalies. Growth stages of positive and negative persistent anomalies that are found in both the Atlantic (ATL) and Pacific (PAC) regions are dominated by autonomous process. For positive anomalies, the net tendencies and resolved forcing patterns resemble large-scale wave trains emanating from the subtropics upstream of the anomaly region. Negative anomaly growth is dominated in both regions by autonomous process to a greater extent that positive anomaly growth. Unresolved forcing is critical in mechanically maintaining persistent anomalies of both signs, but thermally acts in a destructive sense. Decay stages of all anomalies are dominated by resolved forcing. The extent to which local signatures of barotropic and baroclinic energy sources accompany anomaly onset is examined by constructing these terms in the context of a local kinetic energy budget. Redistribution terms in the local kinetic energy budget are important. The representativeness of composites in depicting the dynamics of persistent anomalies is called into question. An examination of the slowly varying local resolved and unresolved forcing during life cycles of individual members of positive anomaly development. 45 refs., 15 figs., 1 tab.
- OSTI ID:
- 5705413
- Journal Information:
- Journal of the Atmospheric Sciences; (United States), Vol. 50:16; ISSN 0022-4928
- Country of Publication:
- United States
- Language:
- English
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