Dust storm

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A dust / sand storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, causing soil to move from one place and deposition in another. The Sahara and drylands around the Arabian peninsula are the main terrestrial sources of airborne dust, with some contributions from Iran, Pakistan and India into the Arabian Sea, and China's significant storms deposit dust in the Pacific. It has been argued that 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, or places where sand is a more prevalent soil type than dirt or rock, 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

As the force of wind passing over loosely held particles increases, particles of sand first start to vibrate, then to saltate ("leap"). As they repeatedly strike the ground, they loosen and break off smaller particles of dust which then begin to travel in suspension. 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.[1]

A recent study finds that the initial saltation of sand particles induces a static electric field by friction. Saltating sand acquires a negative charge relative to the ground which in turn loosens more sand particles which then begin saltating. This process has been found to double the number of particles predicted by previous theories.[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.

Dryland farming is also another cause of dust storms, since dryland farmers rely on rainfall to water their crops, they engage in practices to maintain moisture in the soil. Such practices include leaving a field fallow for a year after harvesting to allow the buildup of water to build in the soil and covering the field with dry earth in an attempt to seal in the underlying. These practices make dryland agriculture susceptible to dust storms. These methods are used by farmers in eastern Washington, an arid region.[3]

Physical and environmental effects

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 (0.99 mi) 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; storms are very common around Khartoum every summer. When it happens you can't see anything but a wall of sand covering your view.

The Sahara desert is a key source of dust storms, particularly the Bodélé Depression[4] and an area covering the confluence of Mauritania, Mali, and Algeria.[5]

Saharan dust storms have increased approximately 10-fold during the half-century since the 1950s, causing topsoil loss in Niger, Chad, northern Nigeria, and Burkina 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.[6][7] 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.[8][9][10]

Dust storms have also been shown to increase the spread of disease across the globe. Virus spores in the ground are blown into the atmosphere by the storms with the minute particles then acting like urban smog or acid rain.[11]

Prolonged and unprotected exposure of the respiratory system in a dust storm can also cause Silicosis which, if left untreated, will lead to Asphyxiation. There is also the danger of keratoconjunctivitis sicca ("dry eyes") which, in severe cases without immediate and proper treatment, can lead to blindness.

Economic impact

Dust storms cause soil loss from the dry lands, 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 rain forests get most of their mineral nutrients from the Sahara; iron-poor ocean regions get iron; and dust in Hawaii increases plantain growth. In northern China as well as the mid-western U.S., ancient dust storm deposits known as loess are highly fertile soils, but they are also a significant source of contemporary dust storms when soil-securing vegetation is disturbed.

Extraterrestrial dust storms

See Mars Dust Storms.

Dust storms are not limited to Earth; see Mars Dust Storms

Notable dust storms

Gallery

Panoramic view of a sandstorm coming through Fallujah, Iraq.

See also

Notes

  1. ^ a b Victor R. Squires. "Physics, Mechanics and Processes of Dust and Sandstorms". Adelaide University, Australia. http://www.unccd.int/publicinfo/duststorms/part1-eng.pdf. Retrieved 2007-07-29. 
  2. ^ Electric Sand Findings, University of Michigan Jan. 6, 2008
  3. ^ a b "Dust Storm in Eastern Washington : Image of the Day". earthobservatory.nasa.gov. http://earthobservatory.nasa.gov/IOTD/view.php?id=40590. Retrieved 2009-10-10. 
  4. ^ 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
  5. ^ 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
  6. ^ ENVIRONMENT: Around the Globe, Farmers Losing Ground Analysis by Lester R. Brown (Jun 27, 2007)
  7. ^ http://www.earth-policy.org/Books/Seg/PB2ch05_ss3.htm LOSING SOIL Lester R. Brown
  8. ^ 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
  9. ^ Storm Report: Dry air inhibits storms Saharan winds limit formation in warm Gulf Jim Bradshaw, 5 July 2007
  10. ^ NASA: Saharan Dust Has Chilling Effect on North Atlantic
  11. ^ Vidal, John (27 September 2009). "Dust storms spread deadly diseases worldwide". London: guardian.co.uk. http://www.guardian.co.uk/world/2009/sep/27/dust-storms-diseases-sydney. Retrieved May 1, 2010. 
  12. ^ http://www.archaeology.org/0009/newsbriefs/cambyses.html
  13. ^ "Sandstorm Kills 12 In Northern Egypt". The New York Times. May 3, 1997. http://www.nytimes.com/1997/05/03/world/sandstorm-kills-12-in-northern-egypt.html. 
  14. ^ "Bahrain day two - sandstorm curtails running at Sakhir". Formula One. February 11, 2009. http://www.formula1.com/news/headlines/2009/2/8923.html. Retrieved July 6, 2011. 
  15. ^ Ramachandran, Arjun (September 23, 2009). "Sydney turns red: dust storm blankets city". The Sydney Morning Herald. http://www.smh.com.au/environment/sydney-turns-red-dust-storm-blankets-city-20090923-g0so.html. 
  16. ^ Chanson, H. (2009). Dust storm over Brisbane on 23 September 2009 - During and After. Working paper, School of Civil Engineering, University of Queensland, Brisbane, Australia, 3 pages. http://espace.library.uq.edu.au/view/UQ:187624. 
  17. ^ "Brisbane on alert as dust storms sweep east". ABC News (Australian Broadcasting Corporation). September 23, 2009. http://www.abc.net.au/news/stories/2009/09/23/2694096.htm. Retrieved July 6, 2011. 
  18. ^ "Big red hits NZ as dust storm crosses Tasman". ABC News (Australian Broadcasting Corporation). http://www.abc.net.au/news/stories/2009/09/25/2696441.htm. 
  19. ^ Terra, MODIS; Rebecca Lindsey (March 20, 2010). "Spring Sandstorm Scours China". Earth Observatory. National Aeronautics and Space Administration. http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=43207. Retrieved 11 April 2010. 
  20. ^ Bodeen, Christopher (March 22, 2010). "China's sandstorms blast Beijing with dust, sand". The Associated Press. http://www.google.com/hostednews/ap/article/ALeqM5jRAywP2HiPafKiAikGO_jlpPj0GwD9EK0DR00. Retrieved 11 April 2010. 
  21. ^ Kanalley, Craig (February 20, 2010). "Beijing Sandstorm 2010: PHOTOS Of Major China Storm". Huffington Post. Associated Press. http://www.huffingtonpost.com/2010/03/20/beijing-sandstorm-2010-ph_n_506875.html. Retrieved July 6, 2011. 
  22. ^ "Dust Storm Swallows Phoenix". The Weather Channel. Associated Press. July 6, 2011. http://www.weather.com/outlook/weather-news/news/articles/phoenix-haboob_2011-07-06. Retrieved July 6, 2011. 
  23. ^ Thompson, Scott (July 6, 2011). "Flights delayed as dust storm hits Phoenix area". CNN. http://www.cnn.com/2011/US/07/06/arizona.dust.storm/index.html?hpt=hp_bn1. Retrieved July 6, 2011. 
  24. ^ "Big Dust Storm Rolls Through Phoenix". myFOXphoenix. July 6, 2011. http://www.myfoxphoenix.com/dpp/weather/big-dust-storm-rolls-into-valley-7-5-2011. Retrieved July 6, 2011. 
  25. ^ Abyssal Storms

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