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Tropopause Undulations and the Development of Extratropical Cyclones. Part II: Diagnostic Analysis and Conceptual Model

Paul A. HirschbergDepartment of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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J. Michael FritschDepartment of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Abstract

A case study of a developing cyclone is used to show that the three-dimensional distribution of height change during development can be strongly sensitive to temperature changes which occur in the lower stratosphere in association with an evolving tropopause undulation. Quantitative analysis of the storm with a geopotential height tendency equation indicates that a synergistic process developed between the stratosphere and troposphere, whereby the vertical motion pattern maintained and intensified the upper-level temperature anomalies while the subsequent upper-level temperature advection led to an enhanced vertical circulation. Using the results of this diagnostic study, a conceptual model is constructed. The conceptual model is based on the hydrostatic and wind-field adjustments that occur as tropopause undulations propagate over favored regions of tropospheric warm advection and less stable air.

Abstract

A case study of a developing cyclone is used to show that the three-dimensional distribution of height change during development can be strongly sensitive to temperature changes which occur in the lower stratosphere in association with an evolving tropopause undulation. Quantitative analysis of the storm with a geopotential height tendency equation indicates that a synergistic process developed between the stratosphere and troposphere, whereby the vertical motion pattern maintained and intensified the upper-level temperature anomalies while the subsequent upper-level temperature advection led to an enhanced vertical circulation. Using the results of this diagnostic study, a conceptual model is constructed. The conceptual model is based on the hydrostatic and wind-field adjustments that occur as tropopause undulations propagate over favored regions of tropospheric warm advection and less stable air.

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