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A mushroom cloud is a distinctive pyrocumulus mushroom-shaped cloud of debris/smoke and usually condensed water vapor resulting from a large explosion. The effect is most commonly associated with a nuclear explosion (and sometimes referred to in this context as a thunderball), but any sufficiently energetic detonation or deflagration will produce the same sort of effect. They can be caused by powerful conventional weapons, like vacuum bombs, including the ATBIP and GBU-43/B Massive Ordnance Air Blast. Some volcanic eruptions and impact events can produce natural mushroom clouds. Mushroom clouds result from the sudden formation of a large volume of lower-density gases at any altitude, causing a Rayleigh–Taylor instability. The buoyant mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a temporary vortex ring that draws up a central column, possibly with smoke, debris, or/and condensed water vapor to form the "mushroom stem". The mass of gas plus entrained moist air eventually reaches an altitude where it is no longer of lower density than the surrounding air; at this point, it disperses, any debris drawn upward from the ground scattering and drifting back down (see fallout). The stabilization altitude depends strongly on the profiles of the temperature, dew point, and wind shear in the air at and above the starting altitude. ==Origin of the term== Although the term appears to have been coined at the start of the 1950s, mushroom clouds generated by explosions were being described centuries before the atomic era. A contemporary aquatint by an unknown artist of the 1782 Franco-Spanish attack on Gibraltar shows one of the attacking force's floating batteries exploding with a mushroom cloud, after the British defenders set it ablaze by firing heated shot. ''The Times'' published a report on 1 October 1937 of a Japanese attack on Shanghai in China which generated "a great mushroom of smoke". The 1917 Halifax Explosion also produced one. During World War II, descriptions of mushroom clouds were relatively common. The atomic bomb cloud over Nagasaki, Japan was described in ''The Times'' of London of 13 August 1945 as a "huge mushroom of smoke and dust." On 9 September 1945, ''The New York Times'' published an eyewitness account of the Nagasaki bombing, written by William L. Laurence, the official newspaper correspondent of the Manhattan Project, who accompanied one of the three aircraft that made the bombing run. He wrote of the bomb producing a "pillar of purple fire", out of the top of which came "a giant mushroom that increased the height of the pillar to a total of 45,000 feet."〔(Eyewitness Account of Atomic Bomb Over Nagasaki ) hiroshima-remembered.com. Retrieved on 2010-08-09.〕 Later in 1946, the Operation Crossroads nuclear bomb tests were described as having a "cauliflower" cloud, but a reporter present also spoke of "the mushroom, now the common symbol of the atomic age." Mushrooms have traditionally been associated both with life and death, food and poison, making them a more powerful symbolic connection than, say, the "cauliflower" cloud. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mushroom cloud」の詳細全文を読む スポンサード リンク
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