Dust storm

A dust storm called sandstorm, 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. Fine particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another. Drylands around North Africa and the Arabian peninsula are the main terrestrial sources of airborne dust, it has been argued that poor management of the Earth's drylands, such as neglecting the fallow system, are increasing dust storm's size and frequency from desert margins and changing both the local and global climate, impacting local economies. The term sandstorm is used most in the context of desert dust storms in the Sahara Desert, 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 to be used when finer particles are blown long distances when the dust storm affects urban areas.

As the force of wind passing over loosely held particles increases, particles of sand first start to vibrate to move across the surface in a process called saltation. As they strike the ground, they loosen and break off smaller particles of dust which 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 and creep. A study from 2008 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 begin saltating; this process has been found to double the number of particles predicted by previous theories. Particles become loosely held due to a prolonged drought or arid conditions, high wind speeds. Gust fronts may be produced by the outflow of rain-cooled air from an intense thunderstorm. Or, the wind gusts may be produced by a dry cold front, that is, a cold front, moving into a dry air mass and is producing no precipitation—the type of dust storm, common during the Dust Bowl 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 and sand storms are most 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, raised is determined by the stability of the atmosphere above the ground as well as by the weight of the particulates. In some cases and sand may be confined to a shallow layer by a low-lying temperature inversion. In other instances, dust may be lifted as high as 20,000 feet 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. One poor farming practice which contributes to dust storms is dryland farming. Poor dryland farming techniques are intensive tillage or not having established crops or cover crops when storms strike at vulnerable times prior to revegetation.

In a semi-arid climate, these practices increase susceptibility to dust storms. However, soil conservation practices may be implemented to control wind erosion. A sandstorm can carry large volumes of sand unexpectedly. Dust storms can carry large amounts of dust, with the leading edge being composed of a wall of thick dust as much as 1.6 km high. Dust and sand storms which come off the Sahara Desert are locally known as a simoon; the haboob is a sandstorm prevalent in the region of Sudan around Khartoum, with occurrences being most common in the summer. The Sahara desert is a key source of dust storms the Bodélé Depression and an area covering the confluence of Mauritania and Algeria. Sahara dust is emitted into the Mediterranean atmosphere and transported by the winds sometimes as far north as central Europe and Great Britain. Saharan dust storms have increased 10-fold during the half-century since the 1950s, causing topsoil loss in Niger, northern Nigeria, 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.

Levels of Saharan dust coming off the east coast of Africa in June 2007 were five times those observed in June 2006, were the highest observed since at least 1999, which may have cooled Atlantic waters enough to reduce hurricane activity in late 2007. Dust storms have 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 and interact with urban air pollution. Short-term effects of exposure to desert dust include immediate increased symptoms and worsening of the lung function in individuals with asthma, increased mortality and morbidity from long-transported dust from both Saharan and Asian dust storms suggesting that long-transported dust storm particles adversely affects the circulatory system. Dust pneumonia is the result of large amounts of dust being inhaled. Prolonged and unprotected exposure of the respiratory system in a dust storm can cause silicosis, which, if left untreated, will lead to asphyxiation.

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Chelyabinsk meteor

The Chelyabinsk meteor was a superbolide that entered Earth's atmosphere over Russia on 15 February 2013 at about 09:20 YEKT. It was caused by an 20 m near-Earth asteroid with a speed of 19.16 ± 0.15 kilometres per second. It became a brilliant superbolide meteor over the southern Ural region; the light from the meteor was brighter than the Sun, visible up to 100 km away. It was observed in neighbouring republics; some eyewitnesses felt intense heat from the fireball. Due to its high velocity and shallow angle of atmospheric entry, the object exploded in an air burst over Chelyabinsk Oblast, at a height of around 29.7 km. The explosion generated a bright flash, producing a hot cloud of dust and gas that penetrated to 26.2 km, many surviving small fragmentary meteorites, as well as a large shock wave. The bulk of the object's energy was absorbed by the atmosphere, with a total kinetic energy before atmospheric impact estimated from infrasound and seismic measurements to be equivalent to the blast yield of 400–500 kilotons of TNT range – 26 to 33 times as much energy as that released from the atomic bomb detonated at Hiroshima.

The object was undetected before its atmospheric entry, in part because its radiant was close to the Sun. Its explosion created panic among local residents, about 1,500 people were injured enough to seek medical treatment. All of the injuries were due to indirect effects rather than the meteor itself from broken glass from windows that were blown in when the shock wave arrived, minutes after the superbolide's flash; some 7,200 buildings in six cities across the region were damaged by the explosion's shock wave, authorities scrambled to help repair the structures in sub-freezing temperatures. With an estimated initial mass of about 12,000–13,000 tonnes, measuring about 20 m in diameter, it is the largest known natural object to have entered Earth's atmosphere since the 1908 Tunguska event, which destroyed a wide, remote and sparsely populated area of Siberia; the Chelyabinsk meteor is the only meteor confirmed to have resulted in a large number of injuries. No deaths were reported; the earlier-predicted and well-publicized close approach of a larger asteroid on the same day, the 30 m 367943 Duende, occurred about 16 hours later.

Local residents witnessed bright burning objects in the sky in Chelyabinsk, Sverdlovsk and Orenburg Oblasts, the Republic of Bashkortostan, in neighbouring regions in Kazakhstan, when the asteroid entered the Earth's atmosphere over Russia. Amateur videos showed a fireball streaking across the sky and a loud boom several minutes afterwards; some eyewitnesses felt intense heat from the fireball. The event began at 09:20:21 Yekaterinburg time, several minutes after sunrise in Chelyabinsk, minutes before sunrise in Yekaterinburg. According to eyewitnesses, the bolide appeared brighter than the sun, as was confirmed by NASA. An image of the object was taken shortly after it entered the atmosphere by the weather satellite Meteosat 9. Witnesses in Chelyabinsk said that the air of the city smelled like "gunpowder", "sulfur" and "burning odors" starting about 1 hour after the fireball and lasting all day; the visible phenomenon due to the passage of an asteroid or meteoroid through the atmosphere is called a meteor.

If the object reaches the ground it is called a meteorite. During the Chelyabinsk meteoroid's traversal, there was a bright object trailing smoke an air burst that caused a powerful blast wave; the latter was the only cause of the damage to thousands of buildings in Chelyabinsk and its neighbouring towns. The fragments entered dark flight and created a strewn field of numerous meteorites on the snow-covered ground; the last time a similar phenomenon was observed in the Chelyabinsk region was the Kunashak meteor shower of 1949, after which scientists recovered about 20 meteorites weighing over 200 kg in total. The Chelyabinsk meteor is thought to be the biggest natural space object to enter Earth's atmosphere since the 1908 Tunguska event, the only one confirmed to have resulted in a large number of injuries, although a small number of panic-related injuries occurred during the Great Madrid Meteor Event of 10 February 1896. Preliminary estimates released by the Russian Federal Space Agency indicated the object was an asteroid moving at about 30 km/s in a "low trajectory" when it entered Earth's atmosphere.

According to the Russian Academy of Sciences, the meteor pushed through the atmosphere at a velocity of 15 km/s. The radiant appears to the left of the rising Sun. Early analysis of CCTV and dashcam video posted online indicated that the meteor approached from the southeast, exploded about 40 km south of central Chelyabinsk above Korkino at a height of 23.3 km, with fragments continuing in the direction of Lake Chebarkul. On 1 March 2013 NASA published a detailed synopsis of the event, stating that at peak brightness, the meteor was 23.3 km high, located at 54.8°N, 61.1°E. At that time it was travelling at about 18.6 km/s, —almost 60 times the speed of sound. In November 2013, results were published based on a more careful calib

Seymour Hess

Seymour Lester Hess was an American meteorologist and planetary scientist. He was born in New York. After earning a bachelor's degree in chemistry from Brooklyn College, in 1943 he entered the University of Chicago as an Army Air Cadet, he completed his master's degree in 1945 following his release from military service as a lieutenant in the United States Army Air Forces, he became a doctoral student in the meteorology department. In 1948 he explored an interest in planetary meteorology, spent his time at the Lowell Observatory in Flagstaff, Arizona observing Mars, his dissertation was titled, Some Aspects of the Meteorology of Mars. On May 20, 1950, Hess had the unusual distinction of reporting a UFO sighting from Flagstaff, saying it was a bright disk cutting through clouds and "definitely was not an airplane". In 1950, he joined the newly formed meteorology department at Florida State University, where he would spend the remainder of his career and twice served as the department chairman.

Starting in 1966, he was associate dean at the University for several years. He served as head of the meteorology science team for the Viking landers, helped design the weather instruments for the Viking 1. On July 21, 1976, he made the first extraterrestrial weather report, giving the atmospheric conditions at Chryse Planitia, Mars. In 1978, he received the Robert O. Lawton Distinguished Professorship, the highest honor awarded by FSU, his work titled Introduction to theoretical meteorology was published in 1959. He died from complications following surgery for cancer. In 1983, the Seymour Hess Memorial Symposium was held in his honor by the International Union of Geodesy and Geophysics. "Seymour Lester Hess ". RR0. Retrieved 2011-07-28. Seymour Hess at Find a Grave