About Dust - test

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Dust storm approaches Wagga Wagga, New South Wales, 6 January 2003. Photo: John Darnley

What is a dust storm?

A dust storm is an area of raised dust that moves with the prevailing wind system. The size of the dust particles can range from 0-1000 micrometers. Dust storms have been known to dust particles as high as 4.5 km into the atmosphere with the average height of a dust storm being 1-2 km. Dust storms can move particles halfway across the Earth and can move as fast as the prevailing weather system.

How are they formed?

In order for a dust storm to develop the wind has to be strong enough to firstly dislodge the dust particles from the surface and then lift them up into the atmosphere.  The minimum wind speed depends on the size of the dust particles, with larger particles needing higher wind speeds to become airborne. In Australia, the minimum wind speed required is about 30km/hr . Once airborne, to lift the dust to high levels, the atmospere must be unstable. This instability can often be created by intense surface heating or the passage of a trough or cold front across the region. Once aloft the dust particles move away from the source region under the influence the pre-dominant upper level winds.

What problems do they cause?

Apart from the obvious characteristic of dust storms reducing visibility to potentially nothing, dust storms also have an effect on the health of both the general population and on some parts of the environment.

Humans can be affected due to the small size of the dust particles, people with breathing related conditions of have trouble when they are trapped in a dust storm. As well as this, dust particles carry microorganisms which can cause increases in disease in areas affected by dust storms.

Coral reefs suffer from the increases in silt in the water, not only does it block the necessary sunlight to the reefs, but it also spawns toxic algal blooms which thrive on the increase in nutrients associated with the dust. Fungal outbreaks in crops such as bananas are known to occur within days of a passing dust storm.

How often do they occur?

Dust storms occur in a very sporadic nature across Australia depending on the amount of rainfall that the arid and semi-arid parts of the country have received. In prolonged dry periods, dust storms are a frequent occurrence, whilst in the wetter periods dust storms are very uncommon due to the increase in vegetation and soil moisture binding dust particles to the surface.

When were the recent dust storms in NSW?

The most recent dust storms to hit the eastern states occurred on:

  • 3 February 2005. A strong cold front brought very cold air up from the south breaking many minimum temperature records. As well as the extreme temperatures, dust storms were recorded in many places west of the divide due to the intense winds. At Bourke, visibility was reduced to 500m, and Moree, visibility reduced to 600m.
  • 23 October 2002. This storm was one of the most severe on record. It was also caused by the passage of a strong cold front. This, combined with high temperatures and the prolonged drought in the region, resulted in a massive dust storm which swept across the eastern states. In Sydney, visibility was reduced to a few kilometres and pilots reported that the dust extended up 3km into the atmosphere. West of the divide experienced the most severe conditions, with many areas experiencing visibilities of just 300m. In the suburb of Roma, in southwestern Queensland, visibility was reduced to just 100m.

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Moree - 23 October 2002

Dust Storm over Eastern Australia, 23/10/2002 [Satellite image originally processed by the Bureau of Meteorology from the polar orbiting satellite Feng Yun-1D operated by the China Meteorological Administration]

Major dust storms in the past which have effected Sydney have occurred in:

  • April 1994.
  • September 1968.
  • December 1957.
  • January 1942, the most severe dust storm to hit the city-reduced visibility at Sydney airport to 500 metres.

What is a dust devil?

A dust devil is a localised dust filled vortex similar in shape to a tornado but of much less strength. They differ from dust storms in that they are a more localised and short-lived event. They form due to intense heating at the surface causing a rapid upward movement of parcel of air. This displacement of the surface air causes an inward movement of surrounding air, creating the common spiral shape of the dust devil. Dust devils are generally small in size compared with tornadoes, being about 3-100m in diameter and up to 300m high. Wind speeds inside the vortex reach a maximum of 100km/hr.

NSW Regional Office, May 2006