DUST STORM

A 'dust storm' or 'sandstorm' is a meteorological phenomenon common in arid and semi-arid regions and arises when a gust front passes or when the wind force exceeds the threshold value where loose sand and dust are removed from the dry surface. Particles are transported by saltation and suspension, causing soil erosion from one place and deposition in another. The Sahara and drylands around the Arabian peninsula are the main source of airborne dust, with some contributions from Iran, Pakistan and India into the Arabian Sea, and China's storms deposit dust in the Pacific. Recently, poor management of the Earth's drylands, such as neglecting the fallow system, are increasing dust storms from desert margins and changing both the local and global climate, and also impacting local economies.^[1]
The term '''sandstorm''' is used most often in the context of desert sandstorms, especially in the Sahara, when, in addition to fine particles obscuring visibility, a considerable amount of larger sand particles are blown closer to the surface. The term '''dust storm''' is more likely to be used when finer particles are blown long distances, especially when the dust storm affects urban areas.

Contents

Causes

Physical and environmental impacts

Economic Impact

Extraterrestrial Dust Storms

Notable dust storms

Gallery

From space

See also

References

External links

Causes

As the force of wind passing over loosely held particles increases, the smallest particles first start to vibrate, then to saltate ("leap"), and to travel in suspension and to land again possibly bouncing or causing other particles to move. At wind speeds above that which causes the smallest to suspend, there will be a population of dust grains moving by a range of mechanisms: suspension, saltation and creep.^[2]
Particles become loosely held mainly due to drought or arid conditions, and wind has varied causes. Gust fronts may be produced by the outflow of rain-cooled air from an intense thunderstorm, or they may represent a dry cold front, that is, a cold front that is moving into a dry air mass and is producing no precipitation. This is the type of dust storm which was common during the Dustbowl years in the U.S. Following the passage of a dry cold front, convective instability resulting from cooler air riding over heated ground can maintain the dust storm initiated at the front. In desert areas, dust and sand storms are most commonly caused by either thunderstorm outflows, or by strong pressure gradients which cause an increase in wind velocity over a wide area. The vertical extent of the dust or sand that is raised is largely determined by the stability of the atmosphere above the ground as well as by the weight of the particulates. In some cases, dust and sand may be confined to a relatively shallow layer by a low-lying temperature inversion. In other instances, dust (but not sand) may be lifted as high as 20,000 feet (6,100 m) high.
Drought and wind contribute to the emergence of dust storms, as do poor farming and grazing practices by exposing the dust and sand to the wind.

Physical and environmental impacts

A sandstorm can move whole sand dunes. Dust storms can carry large amounts of dust, so much so that the leading edge of one can appear as a solid wall of dust as much as 1.6 km (1 mile) high. Dust and sand storms which come off the Sahara Desert are locally known as a simoom or simoon (sîmūm, sîmūn). The ''haboob'' (həbūb) is a sandstorm prevalent in the region of Sudan around Khartoum.
The Saharan desert is a key source of dust storms, particularly the Bodélé Depression^[3] and an area covering the confluence of Mauritania, Mali, and Algeria.^[4]
Saharan dust storms have increased approximately 10-fold during the half-century since the 1950s, causing topsoil loss in Niger, Chad, northern Nigeria, and Burkino Faso. In Mauritania there were just two dust storms a year in the early 1960s, but there are about 80 a year today, according to Andrew Goudie, a professor of geography at Oxford University.^[5][6] Levels of Saharan dust coming off the east coast of Africa in June (2007) were five times those observed in June 2006, and were the highest observed since at least 1999, which may cool Atlantic waters enough to slightly reduce hurricane activity in late 2007.^[7][8]

Economic Impact

Dust storms cause soil loss from the drylands, and worse, they preferentially remove organic matter and the nutrient-rich lightest particles, thereby reducing agricultural productivity. Also the abrasive effect of the storm damages young crop plants. Other effects that may impact the economy are: reduced visibility affecting aircraft and road transportation; reduced sunlight reaching the surface; increased cloud formation increasing the heat blanket effect; high level dust sometimes obscures the sun over Florida; effects on human health of breathing dust.
Dust can also have beneficial effects where it deposits: Central and South American rainforests get most of their mineral nutrients from the Sahara; iron-poor oceans regions get iron; and dust in Hawaii increases planton growth.

Extraterrestrial Dust Storms

See Climate of Mars#Effect of dust storms.

Notable dust storms

★ A series of dust storms displaced hundreds of thousands of agricultural workers in the central United States and Canada during the Dust Bowl.

★ A dust storm that occurred near Tucson, Arizona, USA on July 16, 1971 was extensively documented by meteorologists.

★ On the afternoon of February 8, 1983, a huge dust storm originating in the Mallee region of Victoria, Australia covered the city of Melbourne.

★ On Saturday afternoon of February 24, 2007, a large dust storm originating in the West Texas area of Amarillo covered much of the North Texas area. Strong winds caused extensive property damage to fences, roof shingles, and some buildings. The DFW Airport was severely affected, causing extensive flight delays into and out of the DFW area. Area residents suffered respiratory problems and allergic reactions, causing many people to visit hospitals.

★ In June 2007, a large dust storm struck Karachi Pakistan and areas of the Sindh and lower Balochistan, followed by a series of heavy rainfalls which resulted in a death toll of nearly 200.

Gallery

From space

See also

★ Asian Dust

★ Dust Bowl

★ Sirocco

★ Saharan Air Layer

★ Saharan dust

★ Shamal (wind)

References

1. Physics, Mechanics and Processes of Dust and Sandstorms Victor R. Squires 'Dust storms are a symptom of poor land management' ... 'True deserts are rarely the source of dust storms' ... 'desert margins are more often the principal source of damaging dust storms' ... 'Sahara region is the main source of aeolian dust'
2. PHYSICS, MECHANICS AND PROCESSES OF DUST AND SANDSTORMS Victor R. Squires 'Once ejected, these particles move in one of three modes of transport depending on particle size, shape and density ... designated suspension, saltation and creep'
3. The Bodélé depression: a single spot in the Sahara that provides most of the mineral dust to the Amazon forest.
Ilan Koren et al 2006 Environ. Res. Lett. 1 014005 (5pp) doi:10.1088/1748-9326/1/1/014005 'about half of the annual dust supply to the Amazon basin is emitted from a single source: the Bodélé depression'
4. Saharan Dust: Sources and Trajectories N. J. Middleton, A. S. Goudie
Transactions of the Institute of British Geographers, New Series, Vol. 26, No. 2 (2001), pp. 165-181
5. ENVIRONMENT: Around the Globe, Farmers Losing Ground Analysis by Lester R. Brown (Jun 27, 2007)
6. http://www.earth-policy.org/Books/Seg/PB2ch05_ss3.htm LOSING SOIL
Lester R. Brown
7. http://www.sciam.com/article.cfm?alias=scientists-examine-africa&chanId=sa003&modsrc=reuters Scientists examine African dust link to hurricanes
ScientificAmerican.com August 10, 2007
"These last couple months have been the dustiest summer since 1999, about five times as dusty as last year. Right now ocean temperatures are cooler than average," said Amato Evan, a climate researcher at the University of Wisconsin. "There's a big difference compared to the last two years."

8. Storm Report: Dry air inhibits storms Saharan winds limit formation in warm Gulf
Jim Bradshaw, 2007 July 5. Jeff Masters:"Levels of Saharan dust coming off the east coast of Africa in June were five times those observed in June 2006, and were the highest observed since at least 1999"

External links

★ Slide Show of a Dust Storm in Lubbock, Texas on December 15, 2003

★ ''Dust in the Wind''

★ ''Fearful dust storm inspires songwriter'' —origin of Woody Guthrie's song "So Long, It's Been Good To Know You"

★ Video of a dust storm in Al Asad Iraq, April 27, 2005

★ Video of a Sahara Sandstorm

★ Photos of dust storms hosted by the Portal to Texas History.

★ The Bibliography of Aeolian Research

★ ''Storms tear through Texas, neighbor states; Property damage, fires, injuries reported; Arkansas hit hardest ''

★ ''Dallas dust storm causes LAX delays, cancellations''