A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms, supercells are the overall least common and have the potential to be the most severe. Supercells are isolated from other thunderstorms, can dominate the local weather up to 32 kilometres away, they tend to last 2-4 hours. Supercells are put into three classification types: Classic, Low-precipitation, High-precipitation. LP supercells are found in climates that are more arid, such as the high plains of the United States, HP supercells are most found in moist climates. Supercells can occur anywhere in the world under the right pre-existing weather conditions, but they are most common in the Great Plains of the United States in an area known as Tornado Alley and in the Tornado Corridor of Argentina and southern Brazil. Supercells are found isolated from other thunderstorms, although they can sometimes be embedded in a squall line.
Supercells are found in the warm sector of a low pressure system propagating in a north easterly direction in line with the cold front of the low pressure system. Because they can last for hours, they are known as quasi-steady-state storms. Supercells have the capability to deviate from the mean wind. If they track to the right or left of the mean wind, they are said to be "right-movers" or "left-movers," respectively. Supercells can sometimes develop two separate updrafts with opposing rotations, which splits the storm into two supercells: one left-mover and one right-mover. Supercells can be any size – large or small, low or high topped, they produce copious amounts of hail, torrential rainfall, strong winds, substantial downbursts. Supercells are one of the few types of clouds that spawn tornadoes within the mesocyclone, although only 30% or fewer do so. Supercells can occur anywhere in the world under the right weather conditions; the first storm to be identified as the supercell type was the Wokingham storm over England, studied by Keith Browning and Frank Ludlam in 1962.
Browning did the initial work, followed up by Lemon and Doswell to develop the modern conceptual model of the supercell. To the extent that records are available, supercells are most frequent in the Great Plains of the central United States and southern Canada extending into the southeastern U. S. and northern Mexico. Supercells occur in many other mid-latitude regions, including Eastern China and throughout Europe; the areas with highest frequencies of supercells are similar to those with the most occurrences of tornadoes. The current conceptual model of a supercell was described in Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis by Leslie R. Lemon and Charles A. Doswell III.. Supercells derive their rotation through tilting of horizontal vorticity caused by wind shear. Strong updrafts lift the air turning about a horizontal axis and cause this air to turn about a vertical axis; this forms the mesocyclone. A cap or capping inversion is required to form an updraft of sufficient strength.
The cap puts an inverted layer above a normal boundary layer, by preventing warm surface air from rising, allows one or both of the following: Air below the cap warms and/or becomes more moist Air above the cap coolsThis creates a warmer, moister layer below a cooler layer, unstable. When the cap weakens or moves, explosive development follows. In North America, supercells show up on Doppler radar as starting at a point or hook shape on the southwestern side, fanning out to the northeast; the heaviest precipitation is on the southwest side, ending abruptly short of the rain-free updraft base or main updraft. The rear flank downdraft, or RFD, carries precipitation counterclockwise around the north and northwest side of the updraft base, producing a "hook echo" that indicates the presence of a mesocyclone; this "dome" feature appears above the strongest updraft location on the anvil of the storm. It is a result of a powerful updraft. An observer, at ground level too close to the storm is unable to see the overshooting top due to the fact that the anvil blocks the sight of this feature.
The overshooting is visible from satellite images as a "bubbling" amidst the otherwise smooth upper surface of the anvil cloud. An anvil forms when the storm's updraft collides with the upper levels of the lowest layer of the atmosphere, or the tropopause, has nowhere else to go due to the laws of fluid dynamics- pressure and density; the anvil is cold and precipitation free though virga can be seen falling from the forward sheared anvil. Since there is so little moisture in the anvil, winds can move freely; the clouds take on their anvil shape when the rising air reaches 15,200 -- more. The anvil's distinguishing feature is. In some cases, it can shear backwards, called a backsheared anvil, another sign of a strong updraft; this area on the southern side of the storm in North America
Leota is a census-designated place in Leota Township, Nobles County, United States. The population was 209 at the 2000 census. According to the United States Census Bureau, the CDP has a total area of 1.4 square miles, all of it land. Leota is situated on the western side of the Buffalo Ridge, the drainage divide between the Mississippi River and Missouri River systems. Main highways include: Nobles County Road 19 Nobles County Road 20 The town of Leota was named after Leota Township in which it is located; the story has it that Leota was the name of a young Indian woman who figured in a romantic story familiar to W. G. Barnard, one of the township's first residents; however existence of such a story cannot be verified. If true, Leota Township are the only place names in all of Nobles County that memorialize specific Native Americans; the town of Leota is situated on sections 8 of the township. Leota was established in 1891 as a settlement of Dutch Farmers who migrated northward from another Dutch Settlement in Orange City, Iowa.
The first building erected. In 1891, John DeBoer, Nick DeBoer, James TenCate erected a second building that became Leota's first general store. A post office was established in 1893, the Christian Reformed Church was built in 1898; the town was surveyed by M. S. Smith for James TenCate, the plat was dedicated on January 1, 1902. Leota was never incorporated; the U. S. Census Bureau classifies Leota as a census-designated place. CDPs are populated areas that lack separate municipal government, but which otherwise physically resemble incorporated places; as of the census of 2000, there were 230 people, 113 households, 76 families residing in the CDP. The population density was 169.0 people per square mile. There were 122 housing units at an average density of 89.6/sq mi. The racial makeup of the CDP was 100.00% White. Hispanic or Latino of any race were 0.87% of the population. There were 113 households out of which 17.7% had children under the age of 18 living with them, 64.6% were married couples living together, 1.8% had a female householder with no husband present, 31.9% were non-families.
31.9% of all households were made up of individuals and 23.9% had someone living alone, 65 years of age or older. The average household size was 2.04 and the average family size was 2.52. In the CDP, the population was spread out with 15.7% under the age of 18, 4.3% from 18 to 24, 17.0% from 25 to 44, 24.3% from 45 to 64, 38.7% who were 65 years of age or older. The median age was 58 years. For every 100 females, there were 91.7 males. For every 100 females age 18 and over, there were 86.5 males. The median income for a household in the CDP was $30,568, the median income for a family was $35,625. Males had a median income of $27,019 versus $30,714 for females; the per capita income for the CDP was $15,664. About 10.6% of families and 8.5% of the population were below the poverty line, including 7.0% of those under the age of eighteen and 16.5% of those sixty five or over. Leota is located in Minnesota's 1st congressional district, represented by Mankato educator Tim Walz, a Democrat. At the state level, Leota is located in Senate District 22, represented by Republican Doug Magnus, in House District 22A, represented by Republican Joe Schomacker.
Village Government: Kenneth Bolkema, Chairman. Leota Township is represented by Nobles County Commissioner Gene Metz
Mid-June 1992 tornado outbreak
The Mid-June 1992 tornado outbreak was one of the largest tornado outbreaks on record, affecting portions of the Central United States from June 14 to June 18, 1992. The outbreak began on June 14 when six tornadoes touched down in Idaho. Fifty-eight tornadoes were reported across portions of the Great Plains on June 15, 65 more were reported over much of the central U. S. on June 16. The 123 tornadoes that touched down on June 15–16 make that two-day span the 5th largest two-day tornado outbreak in U. S. history behind the 1974 Super Outbreak, the May 2004 tornado outbreak sequence, the tornado outbreak of April 14–16, 2011, the 2011 Super Outbreak. Twenty-eight more tornadoes touched down on June 17, 13 more touched down on June 18, giving this outbreak 170 confirmed tornadoes. A major spring storm began developing in the western United States over the weekend of June 13–14, 1992; the storm ejected a minor upper air impulse across the Northern Plains on June 13, triggering severe weather across the extreme northwest corner of South Dakota.
Golf ball sized hail and 10 inches of rain destroyed crops and killed over 500 sheep in Harding County, South Dakota. This event preceded the main storm; as the storm moved to the east over the next several days, it caused 170 tornadoes in the central United States, including an F5 tornado in Chandler, Minnesota. The storm system began to weaken as it moved to the eastern United States on June 18. On Tuesday, June 16, 1992, eastern South Dakota and southwest Minnesota were impacted by the storm as it moved from the Rocky Mountain Region across the Upper Midwest. At least two dozen tornadoes were reported that day, with more than three times that many reports of large hail and strong winds, causing widespread swaths of damage to crops and other personal property across much of eastern South Dakota and southwest Minnesota; the first tornado, spawned by a supercell thunderstorm, touched down in Charles Mix County, South Dakota about 1:00 pm. The last tornado was reported shortly before midnight that evening, ending an 11-hour period of intense severe weather across eastern South Dakota and southwest Minnesota.
Until the record was broken in 2010, the 27 tornadoes that touched down in Minnesota on June 16 mark the largest single day tornado outbreak in Minnesota since accurate records started being kept in 1950. Remarkably there was only one fatality from this outbreak, that coming from an F5 tornado in Chandler, Minnesota. In addition to the F5, three F4 tornadoes were reported in Murray County and Mitchell and McPherson counties in Kansas. Damage estimates for the two days were in excess of $160 million; this outbreak played a large part in a record setting month in June, 1992. The 399 tornadoes that touched down in that month was a United States record at the time, breaking the old record of 335 tornadoes set in May, 1991; this record was broken, when 543 tornadoes touched down during May, 2003. This record, would broken in turn when over 750 tornadoes touched down in April 2011. A tornado touched down shortly near Leota, it destroyed a two-house farmstead just east of Leota as it strengthened and moved northeast toward Chandler and Lake Wilson.
The tornado reached its greatest size and strength as it came over the hill south of Chandler, moving into the residential area of west Chandler at 5:18 pm. The tornado destroyed more than 75 homes with another 90 homes, 10 businesses, a church and school damaged, it caused over $50 million in property damage, causing more than 40 injuries. Based on damage assessment by the National Weather Service, this tornado was at F5 intensity as it moved through the residential area of Chandler, where homes were swept away and vehicles were thrown hundreds of yards and stripped down to their frames; the twister was on the ground for over an hour, traveling 35 miles across southwest Minnesota, from northwest Nobles County, through Murray County, into southeast Lyon County. It had a maximum width of.75 miles in the Chandler-Lake Wilson area. This was the only F5 tornado to occur in the United States in 1992. In addition to the severe weather, another devastating weather event was taking place across northeastern South Dakota.
Heavy rains were occurring in an area saturated by previous rains. Over a two- to three-day period in mid-June 1992, 15 to 20 inches of rain fell in the Clear Lake-Watertown area of northeast South Dakota, resulting in widespread flooding throughout the area, major downstream flooding of the Big Sioux River. List of Minnesota weather records List of North American tornadoes and tornado outbreaks List of SPC High Risk days
A tornado is a rotating column of air, in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. The windstorm is referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, they are visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 110 miles per hour, are about 250 feet across, travel a few miles before dissipating; the most extreme tornadoes can attain wind speeds of more than 300 miles per hour, are more than two miles in diameter, stay on the ground for dozens of miles. Various types of tornadoes include the multiple vortex tornado and waterspout. Waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud.
They are classified as non-supercellular tornadoes that develop over bodies of water, but there is disagreement over whether to classify them as true tornadoes. These spiraling columns of air develop in tropical areas close to the equator and are less common at high latitudes. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirl, steam devil. Tornadoes occur most in North America in central and southeastern regions of the United States colloquially known as tornado alley, as well as in Southern Africa and southeast Europe and southeastern Australia, New Zealand and adjacent eastern India, southeastern South America. Tornadoes can be detected before or as they occur through the use of Pulse-Doppler radar by recognizing patterns in velocity and reflectivity data, such as hook echoes or debris balls, as well as through the efforts of storm spotters. There are several scales for rating the strength of tornadoes; the Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale.
An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers; the similar TORRO scale ranges from a T0 for weak tornadoes to T11 for the most powerful known tornadoes. Doppler radar data and ground swirl patterns may be analyzed to determine intensity and assign a rating; the word tornado comes from the Spanish word tornado. Tornadoes opposite phenomena are the derechoes. A tornado is commonly referred to as a "twister", is sometimes referred to by the old-fashioned colloquial term cyclone; the term "cyclone" is used as a synonym for "tornado" in the often-aired 1939 film The Wizard of Oz. The term "twister" is used in that film, along with being the title of the 1996 tornado-related film Twister. A tornado is "a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, visible as a funnel cloud".
For a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base. Scientists have not yet created a complete definition of the word. Tornado refers to the vortex of wind, not the condensation cloud. A tornado is not visible; this results in the formation of a visible funnel condensation funnel. There is some disagreement over the definition of a condensation funnel. According to the Glossary of Meteorology, a funnel cloud is any rotating cloud pendant from a cumulus or cumulonimbus, thus most tornadoes are included under this definition. Among many meteorologists, the'funnel cloud' term is defined as a rotating cloud, not associated with strong winds at the surface, condensation funnel is a broad term for any rotating cloud below a cumuliform cloud. Tornadoes begin as funnel clouds with no associated strong winds at the surface, not all funnel clouds evolve into tornadoes. Most tornadoes produce strong winds at the surface while the visible funnel is still above the ground, so it is difficult to discern the difference between a funnel cloud and a tornado from a distance.
A single storm will produce more than one tornado, either or in succession. Multiple tornadoes produced by the same storm cell are referred to as a "tornado family". Several tornadoes are sometimes spawned from the same large-scale storm system. If there is no break in activity, this is considered a tornado outbreak. A period of several successive days with tornado outbreaks in the same general area is a tornado outbreak sequence called an extended tornado outbreak. Most tornadoes take on the appearance of a narrow funnel, a few hundred yards across, with a small cloud of debris near the ground. Tornadoes may
A wind turbine, or alternatively referred to as a wind energy converter, is a device that converts the wind's kinetic energy into electrical energy. Wind turbines are manufactured in a wide range of horizontal axis; the smallest turbines are used for applications such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Larger turbines can be used for making contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, are becoming an important source of intermittent renewable energy and are used by many countries as part of a strategy to reduce their reliance on fossil fuels. One assessment claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and... the most favourable social impacts" compared to photovoltaic, geothermal and gas. The windwheel of Hero of Alexandria marks one of the first recorded instances of wind powering a machine in history.
However, the first known practical wind power plants were built in Sistan, an Eastern province of Persia, from the 7th century. These "Panemone" were vertical axle windmills, which had long vertical drive shafts with rectangular blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, were used in the gristmilling and sugarcane industries. Wind power first appeared in Europe during the Middle Ages; the first historical records of their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch windmills were in use to drain areas of the Rhine delta. Advanced wind turbines were described by Croatian inventor Fausto Veranzio. In his book Machinae Novae he described vertical axis wind turbines with V-shaped blades; the first electricity-generating wind turbine was a battery charging machine installed in July 1887 by Scottish academic James Blyth to light his holiday home in Marykirk, Scotland.
Some months American inventor Charles F. Brush was able to build the first automatically operated wind turbine after consulting local University professors and colleagues Jacob S. Gibbs and Brinsley Coleberd and getting the blueprints peer-reviewed for electricity production in Cleveland, Ohio. Although Blyth's turbine was considered uneconomical in the United Kingdom, electricity generation by wind turbines was more cost effective in countries with scattered populations. In Denmark by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW; the largest machines were on 24-meter towers with four-bladed 23-meter diameter rotors. By 1908, there were 72 wind-driven electric generators operating in the United States from 5 kW to 25 kW. Around the time of World War I, American windmill makers were producing 100,000 farm windmills each year for water-pumping. By the 1930s, wind generators for electricity were common on farms in the United States where distribution systems had not yet been installed.
In this period, high-tensile steel was cheap, the generators were placed atop prefabricated open steel lattice towers. A forerunner of modern horizontal-axis wind generators was in service at Yalta, USSR in 1931; this was a 100 kW generator on a 30-meter tower, connected to the local 6.3 kV distribution system. It was reported to have an annual capacity factor of 32 percent, not much different from current wind machines. In the autumn of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont; the Smith–Putnam wind turbine only ran for 1,100 hours before suffering a critical failure. The unit was not repaired, because of a shortage of materials during the war; the first utility grid-connected wind turbine to operate in the UK was built by John Brown & Company in 1951 in the Orkney Islands. Despite these diverse developments, developments in fossil fuel systems entirely eliminated any wind turbine systems larger than supermicro size. In the early 1970s, anti-nuclear protests in Denmark spurred artisan mechanics to develop microturbines of 22 kW.
Organizing owners into associations and co-operatives lead to the lobbying of the government and utilities and provided incentives for larger turbines throughout the 1980s and later. Local activists in Germany, nascent turbine manufacturers in Spain, large investors in the United States in the early 1990s lobbied for policies that stimulated the industry in those countries. Wind Power Density is a quantitative measure of wind energy available at any location, it is the mean annual power available per square meter of swept area of a turbine, is calculated for different heights above ground. Calculation of wind power density includes the effect of air density. Wind turbines are classified by the wind speed they are designed for, from class I to class III, with A to C referring to the turbulence intensity of the wind. Conservation of mass requires that the amount of air exiting a turbine must be equal. Accordingly, Betz's law gives the maximal achievable extraction of wind power by a wind turbine as 16/27 of the total kinetic energy of the air flowing through the turbine.
The maximum theoretical power output of a wind machine is thus 16/27 times the kinetic energy of the air passing through the effective disk area of the machine. If the effective area of the disk is A, the wind velocity v, the maximum theoretical power output P is: P = 16
Mitchell, South Dakota
Mitchell is a city in and the county seat of Davison County, South Dakota, United States. The population was 15,254 at the 2010 census. Mitchell is the principal city of the Mitchell Micropolitan Statistical Area, which includes all of Davison and Hanson counties; the first settlement at Mitchell was made in 1879. Mitchell was incorporated in 1883, it was named for Milwaukee banker Alexander Mitchell, President of the Chicago, St. Paul Railroad. Mitchell is located at 43°42′50″N 98°1′35″W, on the James River. According to the United States Census Bureau, the city has a total area of 12.14 square miles, of which, 11.14 square miles is land and 1.00 square mile is water. Mitchell has been assigned the ZIP code 57301 and the FIPS place code 43100. Mitchell has a humid continental climate, like much of the Midwestern United States, with cold, sometimes snowy winters, hot, sometimes humid summers. Average daytime summer temperatures range from 86 °F during the day, 62 °F during the night, winter daytime temperatures average 26 °F during the day, 4 °F during the night.
Most of the precipitation falls during the summer months, the wettest month being June, with an average of 3.52 inches of rain, the driest month is January, with only 0.47 inches of rain. Mitchell is located in Tornado Alley, so thunderstorms spawning tornadoes, can be expected; the campus of Dakota Wesleyan University is located in southwest Mitchell. As of the census of 2010, there were 15,254 people, 6,696 households, 3,641 families residing in the city; the population density was 1,369.3 inhabitants per square mile. There were 7,120 housing units at an average density of 639.1 per square mile. The racial makeup of the city was 93.6% White, 0.5% African American, 3.0% Native American, 0.5% Asian, 0.1% Pacific Islander, 0.6% from other races, 1.8% from two or more races. Hispanic or Latino of any race were 1.7% of the population. There were 6,696 households of which 26.4% had children under the age of 18 living with them, 41.1% were married couples living together, 9.5% had a female householder with no husband present, 3.7% had a male householder with no wife present, 45.6% were non-families.
38.3% of all households were made up of individuals and 15.7% had someone living alone, 65 years of age or older. The average household size was 2.16 and the average family size was 2.88. The median age in the city was 36.8 years. 22.6% of residents were under the age of 18. The gender makeup of the city was 48.8% male and 51.2% female. As of the census of 2000, there were 14,558 people, 6,121 households, 3,599 families residing in the city; the population density was 1,475.7 people per square mile. There were 6,555 housing units at an average density of 664.4 per square mile. The racial makeup of the city was 95.63% White, 0.32% African American, 2.40% Native American, 0.45% Asian, 0.03% Pacific Islander, 0.29% from other races, 0.87% from two or more races. Hispanic or Latino of any race were 0.77% of the population. There were 6,121 households out of which 28.9% had children under the age of 18 living with them, 46.6% were married couples living together, 9.1% had a female householder with no husband present, 41.2% were non-families.
34.3% of all households were made up of individuals and 15.0% had someone living alone, 65 years of age or older. The average household size was 2.27 and the average family size was 2.95. In the city, the population was spread out with 24.1% under the age of 18, 13.4% from 18 to 24, 25.3% from 25 to 44, 19.6% from 45 to 64, 17.6% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 91.9 males. For every 100 females age 18 and over, there were 89.4 males. As of 2000 the median income for a household in the city was $31,308, the median income for a family was $43,095. Males had a median income of $30,881 versus $20,794 for females; the per capita income for the city was $17,888. About 8.8% of families and 12.8% of the population were below the poverty line, including 12.7% of those under age 18 and 10.9% of those age 65 or over. Mitchell is home of the Corn Palace; the Corn Palace is decorated with several colors of dried corn and grains. The theme of the external murals is changed yearly at fall harvest.
The building itself is used for several purposes including a basketball arena, the local high school prom, trade shows, staged entertainment, the Shriner's Circus. Mitchell is the home of the Dakota Discovery Museum, whose mission is to present and preserve the history of the prairie and the people who settled it; the museum covers the time period from 1600, when the Native Americans were still undiscovered, to 1939, the end of the Great Depression. The museum holds one of the most complete and pristine collections of American Indian quill and bead-works; the Dakota Discovery Museum features artists such as Harvey Dunn, James Earle Fraser, Charles Hargens and Oscar Howe. In the village area behind the main building are four authentic historical buildings, including an 1885 one-room school house and the furnished 1886 Victorian-Italianate home of the co-founder of the Corn Palace, Louis Beckwith. Two new features of the museum are Discovery Land, a hands-on activity area for children ages five to ten, the Heritage Gardens Project, which brings indigenous plants to the gardens surrounding the museum and historical buildings.
The Mitchell Prehistoric India
Loess is a clastic, predominantly silt-sized sediment, formed by the accumulation of wind-blown dust. Ten percent of the Earth's land area is covered by similar deposits. Loess is an aeolian sediment formed by the accumulation of wind-blown silt in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate, it is homogeneous and porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs. The word loess, with connotations of origin by wind-deposited accumulation, came into English from German Löss, which can be traced back to Swiss German and is cognate with the English word loose and the German word los, it was first applied to Rhine River valley loess about 1821. Loess is homogeneous, friable, pale yellow or buff coherent non-stratified and calcareous. Loess grains are angular with little polishing or rounding and composed of crystals of quartz, feldspar and other minerals.
Loess can be described as a dust-like soil. Loess deposits may become thick, more than a hundred meters in areas of China and tens of meters in parts of the Midwestern United States, it occurs as a blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess stands in either steep or vertical faces; because the grains are angular, loess will stand in banks for many years without slumping. This soil has a characteristic called vertical cleavage which makes it excavated to form cave dwellings, a popular method of making human habitations in some parts of China. Loess will erode readily. In several areas of the world, loess ridges have formed that are aligned with the prevailing winds during the last glacial maximum; these are called "paha ridges" in "greda ridges" in Europe. The form of these loess dunes has been explained by a combination of tundra conditions. Loess comes from the German Löss or Löß, from Alemannic lösch meaning drop as named by peasants and masons along the Rhine Valley.
The term "Löß" was first described in Central Europe by Karl Cäsar von Leonhard who reported yellowish brown, silty deposits along the Rhine valley near Heidelberg. Charles Lyell brought this term into widespread usage by observing similarities between loess and loess derivatives along the loess bluffs in the Rhine and Mississippi. At that time it was thought that the yellowish brown silt-rich sediment was of fluvial origin being deposited by the large rivers, it wasn't until the end of the 19th century that the aeolian origin of loess was recognized the convincing observations of loess in China by Ferdinand von Richthofen. A tremendous number of papers have been published since focusing on the formation of loess and on loess/palaeosol sequences as archives of climate and environment change; these water conservation works were carried out extensively in China and the research of Loess in China has been continued since 1954. Much effort was put into the setting up of regional and local loess stratigraphies and their correlation.
But the chronostratigraphical position of the last interglacial soil correlating to marine isotope substage 5e has been a matter of debate, owing to the lack of robust and reliable numerical dating, as summarized for example in Zöller et al. and Frechen, Horváth & Gábris for the Austrian and Hungarian loess stratigraphy, respectively. Since the 1980s, thermoluminescence, optically stimulated luminescence and infrared stimulated luminescence dating are available providing the possibility for dating the time of loess deposition, i.e. the time elapsed since the last exposure of the mineral grains to daylight. During the past decade, luminescence dating has improved by new methodological improvements the development of single aliquot regenerative protocols resulting in reliable ages with an accuracy of up to 5 and 10% for the last glacial record. More luminescence dating has become a robust dating technique for penultimate and antepenultimate glacial loess allowing for a reliable correlation of loess/palaeosol sequences for at least the last two interglacial/glacial cycles throughout Europe and the Northern Hemisphere.
Furthermore, the numerical dating provides the basis for quantitative loess research applying more sophisticated methods to determine and understand high-resolution proxy data, such as the palaeodust content of the atmosphere, variations of the atmospheric circulation patterns and wind systems, palaeoprecipitation and palaeotemperature. According to Pye, four fundamental requirements are necessary for the formation of loess: a dust source, adequate wind energy to transport the dust, a suitable accumulation area, a sufficient amount of time. Periglacial loess is derived from the floodplains of glacial braided rivers that carried large volumes of glacial meltwater and sediments from the annual melting of continental icesheets and mountain icecaps during the spring and summer. During the autumn and winter, when melting of the icesheets and icecaps ceased, the flow of meltwater down these rivers either ceased or was reduced; as a consequence, large parts of the submerged and unvegetated floodplains of these braided rivers dried out and were exposed to the wind.
Because these floodplains consist of sediment containing a high content of glacial