Joined: 26 Mar 2008
|Posted: Tue Jul 07, 2009 7:50 pm Post subject: Desert-dust storms
Huge Iraq Dust Storm Seen From Space
A giant dust storm that has raged through Iraq and other Middle East countries for more than a week has been imaged by satellite.
Many Iraqis considered the storm to be the worst in living memory, according to news reports. Hundreds of people reported to the hospital for respiratory distress, and the blowing dust interfered with travel by air and on land.
The new picture, released today, comes from NASA's Aqua satellite. It shows the region at the height of the storm July 5.
Dust is known to lift off continents and migrate across oceans. Desert-dust storms whip up and disperse an estimated 2.4 billion tons of soil and dried sediment throughout the Earth's atmosphere annually, scientists estimate. Each gram of dust contains up to a billion bacterial cells, too. As one example of the global circulation, dust and bacteria can lift off the Sahara Desert in Africa and end up in Florida.
On the plus side, dust storms are known to bring much-needed iron to ocean plants. On the downside, dust storms may be linked to lethal epidemics.
The warming of Atlantic Ocean waters in recent decades is largely due to declines in airborne dust from African deserts and lower volcanic emissions, a study this year suggested.
In the new satellite view, parts of the Tigris and Euphrates Rivers are visible because, in some places, the dust is only a veil. In other places, however, the dust is a thick blanket, completely blocking the ground from view. Baghdad is hidden.
July and August are the hottest months of the year in Iraq, according to researchers at NASA's Earth Observatory. Temperatures can reach more than 120 degrees Fahrenheit.
From mid-June through September, a northwest wind - the shamal - blows almost constantly. Periodically, the winds intensify to the 15 knots (about 17 mph) generally required to whisk dust off the ground.
A drought has dried out wetlands and other pockets of moisture in the arid country, which increases the number of places where the shamal can pick up dust. The resulting dust storms can last for days.
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Joined: 26 Mar 2008
|Posted: Wed Sep 23, 2009 10:50 pm Post subject:
|The dusty blanket that wrapped itself around Sydney this morning pushed air pollution levels to 1500 times their normal levels (anything above 200 considered hazardous) - the highest on record, a climate scientist says.
Sydneysiders woke to a red dawn this morning as a thick dust storm caused havoc with transport and raised health fears.
The size of the dust cloud surprised weather experts, who say it has covered half of NSW.
Dr John Leys, principal research scientist with the NSW Department of Climate Change and Water, said initial estimates showed the dust plume stretched 600 kilometres along the NSW coast from Sydney to the Queensland border this morning, dumping up to 75,000 tonnes of dust per hour into the Tasman Sea.
"It's travelled about 1500 kilometres to get to Sydney," Dr Leys said.
Chris Eiser, manager of atmospheric science at the department, said measurements taken in Sydney today showed the highest level of particle concentration on record.
A normal day would see around 10 micrograms of particles per cubic metre of air and a bushfire might generate 500 micrograms.
Today, levels soared to 15,400 micrograms per cubic metre of air at one location.
"During a dust storm, that’s when we get our highest levels historically and this is the highest we’ve measured in Sydney," Mr Eiser said.
Bureau of Meteorology regional director Barry Hanstrum said it was unusual to see such a wide area covered by dust.
"It's a very unusual event to see a blanket of thick dust like this cover such a large area of NSW," Mr Hanstrum said.
"We see [dust storms] fairly regularly but what we don't see is dust this thick make it across to the coast.
"More than half the state at midday today is under this cloud and the dust is starting to spread north and east and is likely to affect parts of Queensland as well in the next 24 hours."
The haze would not disappear until the low pressure system over Sydney - which brought the dusty winds - moved out to sea, most likely in the evening.
"We should see an improvement in the Sydney area later today but it will be slow, and overnight and into tomorrow we'll see a return to more typical conditions for this time of year," Mr Hanstrum said.
"As the low pressure system moves away, then it will continue to transport the dust out to sea.
"And as winds become more south-westerly, it will bring air from further south and that area wasn't affected by dust storms."
Josh Fisher, meteorologist from weatherzone.com.au, said there was a "ridge of high pressure ... edging east" that was also causing winds to ease.
Most dust would be carried out to sea by the low pressure system, but some would settle to the ground, Mr Hanstrum said.
He also described how the dust cloud this morning had morphed from crimson red about dawn, through orange and yellow and into a paler grey late this morning.
"With the low sun angle first thing in the morning, it's a bit like the angle of the sun at sunset ... you see a reddish tinge in the sky.
"As it got higher in the sky the colour of the dust cloud changed. Now currently it's a grey pall that's over the city and that's because the sun is pretty well directly overhead."
The dusty cloak would keep temperatures in the low 20s today, Mr Fisher said.
"The dust haze will work to keep temperatures lower and, as it clears, the winds are going to turn more south-westerly, bringing in cooler air and some cloud cover with that.
"We'll see temperatures struggle to reach 20 degrees today."
The dust wreaked havoc across town today, crippling the transport system, halting construction work and raising fears about its impact on the health of Sydneysiders.
The RTA advised motorists to exercise caution and ferries were suspended earlier this morning.
The NSW Fire Brigades received more than 500 calls between 3am and 7am, triggered after dust particles entered fire alarms and set them off.
"This is one for the books," a spokesman said.
Sydney Airport was crippled by the storm, with long delays to domestic and international flights expected throughout the day.
Qantas international flights bound for Sydney were diverted to Brisbane and Melbourne, Qantas said in a statement.
"We encourage any passengers with non-essential travel arrangements to reconsider their travel plans for the day," it said.
"Passengers wishing to cancel their flights today (domestic only) will be offered a refund or the opportunity to change their booking without penalty."
Construction work was also shut down on many sites because of the dust and winds.
"Many workers have been experiencing respiratory problems and the winds have made much of the construction work too dangerous to carry out," the Construction, Forestry, Mining & Energy Union said in a statement.
Health fears were also raised, with the Ambulance Service experiencing an increase in calls from asthma sufferers. Some were taken to hospital, a spokeswoman said.