Upper-Level Frontogenesis: Two Case Studies from the FRONTS 87 Experiment

Konstantinos Lagouvardos Centre de Recherches en Physique de l'Environnement/CNET/CNRS, Issy les Moulineaux, France

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Vassiliki Kotroni Centre de Recherches en Physique de l'Environnement/CNET/CNRS, Issy les Moulineaux, France

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Abstract

This study describes the structure of two cold fronts observed during the European experiment FRONTS 87. The selection of these two particular cases is based on the existence of well-marked upper-level features, such as strong jet streams, upper-level frontal discontinuities, and high values of upper-tropospheric potential vorticity. Data from temporally dense radiosoundings are treated, permitting a description of the vertical structure of the frontal atmosphere. Numerical solution of the Sawyer-Eliassen equation provided a depiction of the ageostrophic circulation that developed around the upper-level frontal zone. A comparison of the observed circulations with the potential vorticity structure and earlier observational and numerical studies is performed.

Abstract

This study describes the structure of two cold fronts observed during the European experiment FRONTS 87. The selection of these two particular cases is based on the existence of well-marked upper-level features, such as strong jet streams, upper-level frontal discontinuities, and high values of upper-tropospheric potential vorticity. Data from temporally dense radiosoundings are treated, permitting a description of the vertical structure of the frontal atmosphere. Numerical solution of the Sawyer-Eliassen equation provided a depiction of the ageostrophic circulation that developed around the upper-level frontal zone. A comparison of the observed circulations with the potential vorticity structure and earlier observational and numerical studies is performed.

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