The Growth and Decay of Low-Frequency Anomalies in a GCM

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Abstract
The temporal evolution of a regional-scale persistent low-frequency anomaly is examined with data from a 2100-day perpetual January general circulation model. The persistent episodes are determined with an objective analysis of the low-pass (>10 day) 350-mb streamfunction field that uses both pattern correlations and empirical orthogonal function (EOF) analysis. The composite evolution of each term in the streamfunction tendency equation is calculated relative to the onset day (the first day of the persistent episode). By projecting each term in the streamfunction tendency equation onto an EOF (the EOF is associated with a particular low-frequency anomaly), the contribution of these terms toward the tendency of the corresponding principal component can be obtained. It is found that the sum of the linear terms dominates during most of the growth and the decay of the low-frequency anomaly. The linear term that accounts for the growth and maintenance of the low-frequency anomaly is the interaction b... Abstract The temporal evolution of a regional-scale persistent low-frequency anomaly is examined with data from a 2100-day perpetual January general circulation model. The persistent episodes are determined with an objective analysis of the low-pass (>10 day) 350-mb streamfunction field that uses both pattern correlations and empirical orthogonal function (EOF) analysis. The composite evolution of each term in the streamfunction tendency equation is calculated relative to the onset day (the first day of the persistent episode). By projecting each term in the streamfunction tendency equation onto an EOF (the EOF is associated with a particular low-frequency anomaly), the contribution of these terms toward the tendency of the corresponding principal component can be obtained. It is found that the sum of the linear terms dominates during most of the growth and the decay of the low-frequency anomaly. The linear term that accounts for the growth and maintenance of the low-frequency anomaly is the interaction b...