Prefrontal Troughs over Southern Australia. Part I: A Climatology

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  • 1 Severe Weather Section, Bureau of Meteorology, Perth, Australia
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Abstract

A climatology of the prefrontal westerly trough of southern Australia is presented, based on data for the 10-yr period 1976–85. Trough formation was confined to the longitudes of the Australian continent in the warmer months of the year. An average of approximately 15 troughs/yr were observed, evenly distributed each month from September to April, with appreciable interannual variability in incidence. Troughs formed in advance of a major Southern Ocean cold front in a region of differential thermal advection. Genesis occurred primarily over the west of the continent in spring and autumn, but over southeastern Australia in summer.

Variability in the location of formation at different times of year was related to the seasonal shift of the subtropical ridge over the continent, the shape of the southern continental coastline, and periods of low zonal-index flow. A class of troughs prone to rapid intensification after formation was also identified.

Abstract

A climatology of the prefrontal westerly trough of southern Australia is presented, based on data for the 10-yr period 1976–85. Trough formation was confined to the longitudes of the Australian continent in the warmer months of the year. An average of approximately 15 troughs/yr were observed, evenly distributed each month from September to April, with appreciable interannual variability in incidence. Troughs formed in advance of a major Southern Ocean cold front in a region of differential thermal advection. Genesis occurred primarily over the west of the continent in spring and autumn, but over southeastern Australia in summer.

Variability in the location of formation at different times of year was related to the seasonal shift of the subtropical ridge over the continent, the shape of the southern continental coastline, and periods of low zonal-index flow. A class of troughs prone to rapid intensification after formation was also identified.

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