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Lightning is a sudden electrostatic discharge during an electrical storm between electrically charged regions of a cloud (called intra-cloud lightning or IC), between that cloud and another cloud (CC lightning), or between a cloud and the ground (CG lightning). The charged regions in the atmosphere temporarily equalize themselves through this discharge referred to as a ''strike'' if it hits an object on the ground. Although lightning is always accompanied by the sound of thunder, distant lightning may be seen but be too far away for the thunder to be heard. A lightning strike forms a visible plasma. ==General considerations== On Earth, the lightning frequency is approximately 40–50 times a second or nearly 1.4 billion flashes per year and the average duration is 0.2 seconds made up from a number of much shorter flashes (strokes) of around 30 microseconds.〔http://hyperphysics.phy-astr.gsu.edu/hbase/electric/lightning2.html〕 Many factors affect the frequency, distribution, strength and physical properties of a "typical" lightning flash in a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may also vary by season in middle latitudes. Because human beings are terrestrial and most of their possessions are on the Earth, where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types, even though IC and CC are more common types of lightning. Lightning's relative unpredictability limits a complete explanation of how or why it occurs, even after hundreds of years of scientific investigation. A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process.〔Uman (1986) p. 81.〕 At its peak, a typical thunderstorm produces three or more ''strikes'' to the Earth per minute.〔Uman (1986) p. 55.〕 Lightning primarily occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarizing the atmosphere. However, it can also occur during dust storms, forest fires, tornadoes, volcanic eruptions, and even in the cold of winter, where the lightning is known as thundersnow.〔(New Lightning Type Found Over Volcano? ). News.nationalgeographic.com (February 2010). Retrieved on June 23, 2012.〕 Hurricanes typically generate some lightning, mainly in the rainbands as much as from the center.〔Pardo-Rodriguez, Lumari (Summer 2009) (Lightning Activity in Atlantic Tropical Cyclones: Using the Long-Range Lightning Detection Network (LLDN) ). MA Climate and Society, Columbia University Significant Opportunities in Atmospheric Research and Science Program.〕〔(Hurricane Lightning ), NASA, January 9, 2006.〕〔(The Promise of Long-Range Lightning Detection in Better Understanding, Nowcasting, and Forecasting of Maritime Storms ). Long Range Lightning Detection Network〕 The science of lightning is called ''fulminology'', and the fear of lightning is called astraphobia. 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「Lightning」の詳細全文を読む スポンサード リンク
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