Low-Frequency Waves and Traveling Storm Tracks. Part I: Barotropic Component

Ming Cai Cooperative Institute for Climate Studies, Department of Meteorology, University of Maryland, College Park, Maryland

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Huug M. van den Dool Cooperative Institute for Climate Studies, Department of Meteorology, University of Maryland, College Park, Maryland

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Abstract

We have documented with the observed Northern Hemispheric 500 mb geopotential height data for ten winter seasons that traveling storm tracks exist downstream of the troughs of traveling low-frequency waves. The relation between the low-frequency flow and the traveling storm tracks is discovered with a novel observational technique that records high-frequency activity in a framework traveling along with an identifiable low-frequency structure. The vorticity flux of the high-frequency eddies associated with the traveling storm tracks acts both to reinforce the low-frequency waves and to retard their propagation.

These findings strongly indicate that a substantial amount of the low-frequency variability of the midlatitude atmospheric circulation is attributable to the forcing of the high-frequency eddies. These low-frequency waves organize the high-frequency eddies in such a way that the latter tend to intensify preferentially downstream of the troughs of the former. The symbiotic relation between the low-frequency flow and the traveling storm tracks is dynamically equivalent to the relation between the stationary waves and the stationary storm tracks. This mutual relationship is a necessary although not sufficient condition to parameterize high-frequency eddies in terms of low-frequency flow.

Abstract

We have documented with the observed Northern Hemispheric 500 mb geopotential height data for ten winter seasons that traveling storm tracks exist downstream of the troughs of traveling low-frequency waves. The relation between the low-frequency flow and the traveling storm tracks is discovered with a novel observational technique that records high-frequency activity in a framework traveling along with an identifiable low-frequency structure. The vorticity flux of the high-frequency eddies associated with the traveling storm tracks acts both to reinforce the low-frequency waves and to retard their propagation.

These findings strongly indicate that a substantial amount of the low-frequency variability of the midlatitude atmospheric circulation is attributable to the forcing of the high-frequency eddies. These low-frequency waves organize the high-frequency eddies in such a way that the latter tend to intensify preferentially downstream of the troughs of the former. The symbiotic relation between the low-frequency flow and the traveling storm tracks is dynamically equivalent to the relation between the stationary waves and the stationary storm tracks. This mutual relationship is a necessary although not sufficient condition to parameterize high-frequency eddies in terms of low-frequency flow.

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