White grain

A white grain is a weather phenomenon suddenly and very violent one. It is about a particular grain, which even sometimes does not bring a Précipitations nor of Nuage S. One speaks about “white grain” in reference to the fact that the sky which accompanies it is perfectly clear, and that so he can be announced to the horizon only by one white cloud in fast rise, or by the scum blanchâtre which he generates at the top of the waves.

It is a very abrupt grain, which bursts without any sign heralding, and appears of an incredible violence. Its appearance would be correlated with the formation of an extremely violent downward gust, whose Vent S can sometimes be higher than 300 km/h.

Theory

The air in a stormy environment is hot and wet in bottom, but dry and cold in altitude. When a piece of air becomes hotter than this environment on a given level, it is thorough upwards. Condensation forms a Cumulus budding or Cumulonimbus in which Précipitation develops.

Possibly the heart of rain becomes too heavy to be constant by the ascending Courant which creates the cloud. It is then put to go down. One sees on the image the life cycle of a storm and the arrows show the direction of the movement of the air. In an ordinary storm, that gives a face of more or less strong gusts. However, in a storm where precipitation is very intense and instability (Potential Énergie of Convection Available) important, the downward gust becomes extreme. It is about a sudden collapse of the roadbases of the atmosphere, true a Avalanche of Air which involves violent Turbulence S atmospheric, force of powerful a hurricane, and which lasts of a few seconds to several tens of minutes.

If the downward gust occurs in a very dry environment in the low levels under the storm, downward precipitations evaporate before reaching the ground. The piece of air which contained these precipitations is then colder than the environment, by loss of heat due to evaporation, which accelerates it downwards. There is thus gust without rain and it is what is called a white grain .

This type of grain is very abrupt, bursts without any sign heralding, and can be of an incredible violence. One classify them in macro-gusts (more than 2,5 km) or microphone-gusts (less than 2,5 km) according to the width of the corridor of damage.

The shipwreck of the Albatross of 1961

Ridley Scott has realized in 1996 film Ground swell ( White Squall in English), which reports the Tragédie which struck the sailing Albatross , in 1961.

This solid Navire sank abruptly with broad of the Florida, carrying with him 6 of the 19 members of the crew. According to the testimony of the survivors, the ship would have been taken in a Tempête of a formidable violence. Curiously however, time in the area was with the good shape and no opinion of storm had been announced. Navigator tested, Christopher Sheldon, captain of the Albatross had already wiped many storms during its long career of sailor. However, the tragedy which occurred, remains for him true a Mystère.

The testimony of one of the sailors

A former member of the crew, Chuck Gieg, told that during their voyage, they had undergone good number of rather violent storms, and that each time there had been harbingers leaving time to prepare there. This time, nobody had anything considering coming. According to his newspaper, on May 2nd in the morning towards 8:30, a violent one strong gale fell down on the Albatross which sailed towards Florida; struck by a Rafale of an incredible violence, the boat sank without the crew not having the time of démâter. Strangest according to him, it was that right after the shipwreck, the sea was become again perfectly calm and smooth.

In short, there had been an extremely violent strong gale, which lasted very little of time, less than one minute, perhaps, and the calm one had returned at once after…

See too

Grain (meteorology)
Vague scélérate

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