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Summer scorcher

By Pat, 11 January 2013 News

Fire burning through grassland.

Heatwaves can greatly increase the risk and severity of bushfires.
Image: Malcolm Paterson/CSIRO

In Australia, the year is off to a sizzling start. Much of the continent has been sweltering under a record-breaking heatwave. Let’s look at what’s causing these extreme temperatures.

Heat from the Sun warms areas on the surface of the Earth and air above it. As a volume of air is heated, it expands and the air pressure drops. As air cools, it contracts and the air pressure increases. Weather is complex, but generally speaking, volumes of air move from areas of higher pressure towards areas of lower pressure.

The heating and cooling of air means Earth’s atmosphere doesn’t sit still – volumes of air are moving. We see these changes in the atmosphere by the effects on the weather: temperatures rise and fall, winds change speed and direction, and rain comes and goes away.

The current heatwave started due to a lack of clouds and moisture in central Australia. This caused the air to heat up to high temperatures. This hot, dry air was carried by winds towards the western coast. However, pressure systems prevented the air from blowing out to sea where it would cool down.

The skies have been clear and the Sun keeps shining, meaning more heat and temperatures rising. The volume of hot air has grown in size, and other changes in the atmosphere mean the hot air has moved east across the continent, bringing high temperatures to a large portion of the country.

Australia often experiences heatwaves. What is unusual about this one is that it has affected such a wide area – heatwaves are typically more localised. While there have been some changes in the wind that brought lower temperatures to some parts, a large volume of hot air is still lingering, meaning we haven’t seen the end of the heat yet.

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