Mountain thunderstorms pose significant risks because of their consequences, especially for mountaineers, hikers and paragliders. Despite monitoring weather conditions to prevent accidents, disasters occurring during such phenomena often remain unpredictable and are the subject of novels or other stories.
Thunderstorms are formed when air in a layer of the atmosphere is unstable. [1] A parcel of air raised at the base of this layer is then warmer than the environment and rises. In rising, its temperature decreases by adiabatic expansion, and when the relative humidity of water vapor reaches saturation, this forms a convective cloud. [1] To form a storm, this layer must be very large and the temperature at the top of the cloud must be below −20C.
Mountains can help trigger atmospheric convection in three ways: [2]
In a more general case, several effects may be present and if the synoptic wind is opposed to the anabatic wind, additional convergence occurs at the top of the mountain. [3] It is also possible to create a convergence zone behind the mountain when the synoptic wind can divide and go around it to meet again (ex. Puget Sound Convergence Zone ) that will promote convection. [2]
The uprising serves to not only destabilize the air and form convective clouds, but also to enhance its intensity. [1] As the rising air from the bottom of the slopes is hotter and humid than the surrounding air, the lifted index will be more negative, increasing the vertical extension of the cloud . A simple temperature difference of 2C is enough to greatly aggravate the violence of thunderstorms.
Mountain storms have particularities because of the proximity of clouds, the importance of electric fields, their rapidity of appearance, their particular danger. Sudden wind lift of a mass of air can radically change the initial conditions within them.
Observable phenomena give an idea of the peculiarities of mountain storms .
Mountaineers are the most exposed to these phenomena, [4] in ridges and pass passes.
In addition to the common phenomena related to the storm, larger electric fields cause unexpected warning signs related to the ionization of the air. [5] French mountaineers say they hear "bees": suddenly, on all surfaces, are small noisy discharges. [6] [7] After this bee-sound, another observation is that the hair stands straight up over the head, and sparks can form between the teeth when one opens one's mouth. These are the results of electrical phenomena, already described in other situations, and known by the name of fire of St. Elmo or corona effect also called crown effect. [8]
Climbers, not very mobile, can find themselves trapped in a storm. The metal ice axes of climbing equipment can attract lightning, a great danger in these situations.
The force of thunder, lightning, lightning, rain, hail, bursts and whirlwinds can cause other dangerous situations. Some natural phenomena are increased tenfold by altitude, [9] in particular:
Weather forecasting is an essential tool for preventing accidents related to mountain storms [10] but does not prevent them. Climbers must know how to respond to a storm in the mountains. [11]
In the United States, the National Weather Service provides forecasts for every point in its territory, including the mountainous areas. In other countries, similar services and guidance are provided by the Meteorological Service of Canada, by the UK Met Office, and by Météo France in France. [12] France also maintains a Safe Mountain Foundation [13] and Keraunos, an observatory for violent storms. [14]
A number of mountaineers in the 20th century wrote autobiographical accounts of being caught in mountain storms.
About the 1961 disaster, Mazeaud wrote: "Sitting on my stirrups, I use my piton, when I hear a striking ring somewhat resembling the phone. My companions, forty meters below, prick up their ears. Soon, I feel pain in my fingers, sparks run on my hammer. The carabiners on my shoulder stick to my fingers (...) A pendulum swing puts me near Pierrot, when a flash of a surprising glow hits him in the face, exactly in the ear where his hearing aid blackens. He falls into my arms, haggard, disgusted, without reaction". He also noted that Pierre Kohlmann [19] was not killed instantly but the shock seemed to make him lose his mind. During the several days that it took to descend, he did not say a word, finally collapsing just before reaching the entrance, the last victim of the storm that killed four mountaineers. [20]
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Cumulonimbus is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals, such as snow and graupel, the interaction of which can lead to hail and to lightning formation, respectively. When occurring as a thunderstorm these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes, hazardous winds, and large hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb.
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.
A meteorologist is a scientist who studies and works in the field of meteorology aiming to understand or predict Earth's atmospheric phenomena including the weather. Those who study meteorological phenomena are meteorologists in research, while those using mathematical models and knowledge to prepare daily weather forecasts are called weather forecasters or operational meteorologists.
Gaston Rébuffat was a French alpinist, mountain guide, and author. He is well known as a member of the first expedition to summit Annapurna 1 in 1950 and the first man to climb all six of the great north faces of the Alps. In 1984, he was made an officer in the French Legion of Honour for his service as a mountaineering instructor for the French military. At the age of 64, Gaston Rébuffat died of cancer in Paris, France. The rock-climbing technique, the "Gaston", was named after him. A photo of Rébuffat atop the Aiguille du Roc in the French Alps is on the Voyager Golden Records.
Walter Bonatti was an Italian mountaineer, alpinist, explorer and journalist. He was noted for many climbing achievements, including a solo climb of a new alpine climbing route on the south-west pillar of the Aiguille du Dru in August 1955, the first ascent of Gasherbrum IV in 1958, and, in 1965, the first solo climb in winter of the North face of the Matterhorn on the mountain's centenary year of its first ascent. Immediately after his solo climb on the Matterhorn, Bonatti announced his retirement from professional climbing at the age of 35, and after 17 years of climbing activity. He authored many mountaineering books and spent the remainder of his career travelling off the beaten track as a reporter for the Italian magazine Epoca. He died on 13 September 2011 of pancreatic cancer in Rome aged 81, and was survived by his life partner, the actress Rossana Podestà.
A pulse storm is a single cell thunderstorm of substantial intensity which only produces severe weather for short periods of time. Such a storm weakens and then generates another short burst – hence "pulse".
Atmospheric convection is the result of a parcel-environment instability in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day expands the height of the planetary boundary layer, leading to increased winds, cumulus cloud development, and decreased surface dew points. Convection involving moist air masses leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.
Convective storm detection is the meteorological observation, and short-term prediction, of deep moist convection (DMC). DMC describes atmospheric conditions producing single or clusters of large vertical extension clouds ranging from cumulus congestus to cumulonimbus, the latter producing thunderstorms associated with lightning and thunder. Those two types of clouds can produce severe weather at the surface and aloft.
A storm cell is an air mass that contains up and down drafts in convective loops and that moves and reacts as a single entity, functioning as the smallest unit of a storm-producing system. An organized grouping of thunder clouds will thus be considered as a series of storm cells with their up/downdrafts being independent or interfering one with the other.
The levant is an easterly wind that blows in the western Mediterranean Sea and southern France, an example of mountain-gap wind. In Roussillon it is called "llevant" and in Corsica "levante". In the western Mediterranean, particularly when the wind blows through the Strait of Gibraltar, it is called the Viento de Levante or the Levanter. It is also known as the Solano.
A mesovortex is a small-scale rotational feature found in a convective storm, such as a quasi-linear convective system, a supercell, or the eyewall of a tropical cyclone. Mesovortices range in diameter from tens of miles to a mile or less and can be immensely intense.
The Spanish Plume is a weather pattern in which a plume of warm air moves from the Iberian plateau or the Sahara to northwestern Europe, causing thunderstorms. This meteorological pattern can lead to extreme high temperatures and intense rainfall during the summer months, with potential for flash flooding, damaging hail, and tornado formation. Some of these intense thunderstorms are formed from thermal lows, which are also known as heat lows. Thermal lows can be semipermanent features around some parts of Europe, particularly in the summer season. These thermal lows can be developed or created around Spain, Portugal, France etc., during the summer season because of the intense heat. Thermal low pressure can be located around the world, particularly in the summer or in tropical regions.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
Numerous accidents have occurred in the vicinity of thunderstorms due to the density of clouds. It is often said that the turbulence can be extreme enough inside a cumulonimbus to tear an aircraft into pieces, and even strong enough to hold a skydiver. However, this kind of accident is relatively rare. Moreover, the turbulence under a thunderstorm can be non-existent and is usually no more than moderate. Most thunderstorm-related crashes occur due to a stall close to the ground when the pilot gets caught by surprise by a thunderstorm-induced wind shift. Moreover, aircraft damage caused by thunderstorms is rarely in the form of structural failure due to turbulence but is typically less severe and the consequence of secondary effects of thunderstorms.
This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.
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