Deducing Anomalous Wave Source Regions during the Life Cycles of Persistent Flow Anomalies

Abstract

Anomalous wave source regions are identified during the life cycles of persistent flow anomalies occurring over the North Pacific and North Atlantic Oceans during boreal winter. These cases project strongly upon the Pacific?North American and Eastern Atlantic teleconnection patterns, respectively, and represent two of the primary modes of intraseasonal low frequency variability in the Northern Hemisphere wintertime circulation. In the upper troposphere, these cases are manifested by wave trains of large-scale and large amplitude flow anomalies extending downstream from key regions near the Aleutian Islands and south of Iceland, respectively. The occurrence of persistent flow anomalies is closely linked to persistent extremes in surface weather and to variations in the skill of extended-range weather forecasts. Black and Dole performed a detailed diagnostic analysis of the onset of persistent cyclonic flow anomalies over the North Pacific. A key result of their study was that wave activity flux diagnoses correctly identified the location of anomalous wave source regions. Black and Dole?s study is extended by diagnosing three-dimensional fluxes of wave activity during the onset, maintenance, and decay of cyclonic and anticyclonic persistent flow anomalies over the North Atlantic and North Pacific regions. The flux characterizes large-scale wave propagation, and the flux divergence is used to deduce the location of regional sources and sinks of anomalous wave activity. In all cases there is a marked upward and downstream flux of wave activity emanating from the lower troposphere near the key region. The results are consistent with a local wave source and Rossby-like wave propagation away from the source. There is little evidence that anomalous remote processes directly force persistent flow anomaly life cycles. The diagnostic analyses indicate that the primary anomalous wave sources for both cyclonic and anticyclonic persistent flow anomalies are local to the region of their occurrence. It remains possible, however, that anomalous remote forcing plays an indirect or catalytic role in some cases.