Subsynoptic-Scale Structure in a Major Synoptic-Scale Cyclone

Chris O'Handley Department of Atmospheric Science, State University of New York at Albany, Albany, New York

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Lance F. Bosart Department of Atmospheric Science, State University of New York at Albany, Albany, New York

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Abstract

An analysis of a major cyclone over the eastern United States in late February 1984 revealed the presence of several embedded well-defined mesoscale structures, including a low-level jet, a long-lived snowband and a strong upper-level front. Understanding the importance of these mesoscale features to the evolution of the synoptic-scale cyclone is the basis for this paper.

Evidence is presented that a period of weakening after initial surface cyclogenesis was the result of decoupling of the upper-level trough from the surface cyclone, as a consequence of the development of peripheral mesoscale precipitation systems. Redevelopment on the western side of the Appalachians occurred where orographic subsidence was amplified by a strong mesoscale low-level jet. Further intensification then took place when a strong upper-level frontal zone approached the surface cyclone. An incidental finding is that one of the mesoscale precipitation systems was a snowband, driven by strong synoptic-scale frontogenetical forcing rather than being a spontaneous consequence of conditional symmetric instability.

Abstract

An analysis of a major cyclone over the eastern United States in late February 1984 revealed the presence of several embedded well-defined mesoscale structures, including a low-level jet, a long-lived snowband and a strong upper-level front. Understanding the importance of these mesoscale features to the evolution of the synoptic-scale cyclone is the basis for this paper.

Evidence is presented that a period of weakening after initial surface cyclogenesis was the result of decoupling of the upper-level trough from the surface cyclone, as a consequence of the development of peripheral mesoscale precipitation systems. Redevelopment on the western side of the Appalachians occurred where orographic subsidence was amplified by a strong mesoscale low-level jet. Further intensification then took place when a strong upper-level frontal zone approached the surface cyclone. An incidental finding is that one of the mesoscale precipitation systems was a snowband, driven by strong synoptic-scale frontogenetical forcing rather than being a spontaneous consequence of conditional symmetric instability.

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