Southerly Changes

A passive cold front of importance in south-east Australia is the southerly change. It occurs frequently in spring and summer, bringing welcome relief from the heat. Initially, there is an eastwards, shallow front south of Victoria. The front is then arrested on its northern flank by the mountains of the Dividing Range, which lie parallel to the east coast. This swings the more southerly flank forwards, so that the front now travels northwards, following the coastline. The driving force is the narrow and intense thermal gradient along the coast. It peters out at 100-500 km from the south-east corner of mainland Australia.

The arrival of a southerly change is usually sudden, with a shift of wind direction, an abrupt drop in temperature and the development of low stratus. Particularly powerful squalls of cool southerly wind accompany the change if there are strong westerlies south of Victoria and the coastal areas of New South Wales are hot. Sometimes the southerly wind lasts several hours, especially in the afternoon.

The change on the New South Wales coast is known locally as a Southerly Burster. Similar fronts occur along the east coast of New Zealand's South Island (Figure 13.6), between Sao Paulo and Salvador in Brazil, and near Durban in South Africa.

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