Published by admin on 07 Jun 2009
General Climate
Climate in outline


Australia’s climate is dominated by the dry, sinking air of the subtropical high pressure belt which moves north and south with the seasons. This causes the rainfall pattern over Australia to be strongly seasonal and helps to define the main climate regions shown below.
When the high pressure systems move north during winter, southern Australia comes under the influence of westerly winds and rain-bearing cold fronts. Most of Australia’s primary production occurs in the temperate regions of the south and east, and relies on this winter rainfall. Cold snaps may lead to frosts inland, though temperatures about the coast are generally mild all year round. Summers over southern Australia are mostly dry and hot with coastal sea-breezes. Following a long dry spell, hot, dry winds from the interior can cause bushfires in southern and eastern Australia. The inflammability of the Australian bush (which has adapted to the climate) adds to the risk.
In comparison, tropical regions of northern Australia experience a wet summer as the monsoon moves in. During “the wet”, typically October to April, moist northwesterly winds bring humid conditions with showers and thunderstorms. Rainfall amounts may vary markedly from year-to-year, and occasional tropical cyclones can bring abundant rainfall to tropical coastal regions and possibly further inland. Once the monsoon has retreated, winter brings blue skies and mild, dry conditions. Dryland agriculture and pastoralism have adapted to the harsh climate of the vast inland tropical area.
As a result of the influence of the high pressure belt, much of Australian rainfall is low and variable. Eighty per cent of the continent has an average annual rainfall less than 600 mm. The vegetation of the arid interior adapts to dry conditions and responds quickly when rainfall is received.


Monsoons
Monsoons are seasonal winds and are well developed over Asia and South East Asia. Summer in the northern hemisphere in July heats up the land mass of Asia. This creates a low pressure system over Asia. The winter in the southern hemisphere creates a high pressure system over Australia. Winds therefore blows from the Australian high pressure system across the equator to the Asian low pressure. From Australia, it blows as the south east monsoon and is deflected to the right as it crosses the equator to become the south west monsoon.
In winter, most parts of Asia create a high pressure system because of the cooling of the air. On the other hand, in the southern hemisphere, conditions are reversed and the summer season creates a low pressure system over Australia. Winds blow from the Asian high pressure system as the North east monsoon, crosses the equator and is deflected to the left to reach Australia as the north west monsoon.







