The Australian Summertime Cool Change. Part I: Synoptic and Subsynoptic Scale Aspects

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  • 1 Head Office, Bureau of Meteorology, Melbourne, Australia 3001
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Abstract

In this, the first of a series of three papers on the structure of be summertime cool change of southeastern Australia, the prevailing climatological conditions are established, a background given to each of the cool changes studied and an assessment made of the representativeness of the systems sampled.

A conceptual model of the kinematics of the cool change is presented and is similar to that proposed previously for cold fronts in the Northern Hemisphere. The model includes prefrontal warm and cool ascending “conveyor belts” and subsiding postfrontal streams. The warm conveyor belt was found to have a relatively low moisture content, a consequence of continental effects, and significant recirculation of conveyor belt air into the postfrontal region was observed. Typical vorticity distributions are presented and the applicability of quasi-geostrophic diagnostic techniques to the cool change examined. Geostrophically forced frontogenesis was found to be organized on the subsynoptic scale, was often confined to shallow near-surface layers, and some shallow cool changes appeared only weakly or indirectly coupled to upper tropospheric troughs.

Abstract

In this, the first of a series of three papers on the structure of be summertime cool change of southeastern Australia, the prevailing climatological conditions are established, a background given to each of the cool changes studied and an assessment made of the representativeness of the systems sampled.

A conceptual model of the kinematics of the cool change is presented and is similar to that proposed previously for cold fronts in the Northern Hemisphere. The model includes prefrontal warm and cool ascending “conveyor belts” and subsiding postfrontal streams. The warm conveyor belt was found to have a relatively low moisture content, a consequence of continental effects, and significant recirculation of conveyor belt air into the postfrontal region was observed. Typical vorticity distributions are presented and the applicability of quasi-geostrophic diagnostic techniques to the cool change examined. Geostrophically forced frontogenesis was found to be organized on the subsynoptic scale, was often confined to shallow near-surface layers, and some shallow cool changes appeared only weakly or indirectly coupled to upper tropospheric troughs.

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