Information AboutLightning |
in Romania - 26.06.2007]] in Romania ]] Lightning is an atmospheric discharge of Electricity , which typically occurs during Thunderstorm s, and sometimes during Volcanic Eruptions or Dust Storms . HISTORY OF RESEARCH Beginnings In his '' (which had been known to the Chinese since the Arabs had traded it, or a chemical composition fairly equal to it, in the 10th century).Needham, Joseph (1986). ''Science and Civilization in China: Volume 5, Chemistry and Chemical Technology, Part 7, Military Technology; the Gunpowder Epic''. Taipei: Caves Books Ltd. Pages 80-82. For these strange effects of lightning, Kuo wrote:
Thus was the frustration of learned men in his time of the desire to know the true nature of lightning and other such common phenomena. However, in the Western World the true nature and understanding behind its force would become known by the 18th century. in 1902]] Benjamin Franklin ( 1706 - 1790 ) endeavored to test the theory that sparks shared some similarity with lightning using a spire which was being erected in Philadelphia . While waiting for completion of the spire, he got the idea of using a flying object, such as a Kite , instead. During the next Thunderstorm , which was in June 1752, it was reported that he raised a kite, accompanied by his son as an assistant. On his end of the string he attached a key and tied it to a post with a Silk thread. As time passed, Franklin noticed the loose fibres on the string stretching out; he then brought his hand close to the key and a spark jumped the gap. The rain which had fallen during the storm had soaked the line and made it conductive. Franklin was not the first to perform the kite experiment. Thomas-François Dalibard and De Lors conducted it at Marly-la-Ville Pages 3-4. pdf file in France a few weeks before Franklin's experiment. In his autobiography (written 1771-1788, first published 1790), Franklin clearly states that he performed this experiment after those in France, which occurred weeks before his own experiment, without his prior knowledge as of 1752. According to author Tom Tucker, Franklin never actually performed the famed kite experiment, but rather published his account of it as a hoax, possibly to endanger his detractors.1 Continuing research As news of the experiment and its particulars spread, people attempted to replicate it. However, experiments involving lightning are always risky and frequently fatal. The most well-known death during the spate of Franklin imitators was that of Professor George Richmann , of Saint Petersburg, Russia . He had created a set-up similar to Franklin's, and was attending a meeting of the Academy of Sciences when he heard Thunder . He ran home with his engraver to capture the event for posterity. While the experiment was under way, Ball Lightning appeared, collided with Richmann's head and killed him, leaving a red spot. His shoes were blown open, parts of his clothes singed, the engraver knocked out, the door frame of the room split, and the door itself torn off its hinges. Although experiments from the time of Franklin showed that lightning was a discharge of came into service, engineers needed to know much more about lightning in order to adequately protect lines and equipment. PROPERTIES OF LIGHTNING .]] A bolt of lightning can travel at a speed of 45 s approaching 28,000 °C (50,000 °F ), hot enough to fuse soil or sand into Glass Channels . {Link without Title} An average bolt of lightning carries a negative electric current of 40 of air being three million Volt s ''per'' meter, this works out at about one billion (thousand million) volts for a 300 M (1,000 foot) lightning bolt. With an electric current of 100 kA, this gives a power of 100 trillion (million million) watts. Different locations have different potentials (voltages) and currents for an average lightning strike. For example, Florida, with the United States' largest number of recorded strikes in a given period during the summer season, has very sandy ground in some areas and conductive saturated mucky soil in others. As much of Florida lies on a peninsula, it is bordered by the ocean on three sides. The end result is the daily development of sea and lake breeze boundaries that collide and produce thunderstorms. Arizona, which has very dry, sandy soil and a very dry air, has cloud bases as high as 1800-2100 m (6,000-7,000 feet) above ground level, and gets very long and thin purplish discharges which crackle; while Oklahoma, with cloud bases about 450-600 m (1,500-2,000 feet) above ground level and fairly soft, clay-rich soil, has big, blue-white explosive lightning strikes that are very hot (high current) and cause sudden, explosive noise when the discharge comes. The difference in each case may consist of differences in voltage levels between clouds and ground. Research on this is still ongoing. NASA scientists have also found the radio waves created by lightning clear a safe zone in the radiation belt surrounding the earth. This zone, known as the Van Allen Belt slot, can potentially be a safe haven for satellites, offering them protection from the Sun's radiation. [http://www.space.com/scienceastronomy/planetearth/space_lightning_991216.html Demirkol, M.K.; Inan, Umran S.; Bell, T.F.; Kanekal, S.G.; and Wilkinson, D.C., "Ionospheric effects of relativistic electron enhancement events," ''Geophysical Research Letters'', Vol. 26, No. 23, pages 3557-3560 (December 1999). (Abstract available on-line at: http://adsabs.harvard.edu/abs/1999GeoRL..26.3557D .) The first process in the generation of lightning is still a matter of debate: scientists have studied root causes ranging from atmospheric perturbations ( Wind , Humidity , and Atmospheric Pressure ), to the impact of Solar Wind and accumulation of charged solar particles.[http://www.lightningsafety.noaa.gov/science.htm Large quantities of ice in the clouds are suspected to enhance lightning development. This charge will neutralize itself through any available path. This may assist in the forcible separation of positive and negative Charge Carrier s within a cloud or air, and thus help in the formation of lightning. Lightning can also occur within the ash clouds from Volcanic Eruptions ,2 Account of ash lightning. See 5th paragraph.3 or can be caused by violent Forest Fire s which generate sufficient dust to create a Static Charge . FORMATION ;Note: Positive Lightning (a rarer form of lightning that originates from positively charged regions of the thundercloud) does not generally fit the following pattern. Charge separation The first process in the generation of lightning is charge separation. Polarization mechanism theory # Falling droplets of ice and rain become electrically polarized as they fall through the atmosphere's natural electric field; # Colliding ice particles become charged by Electrostatic Induction . Electrostatic induction theory Another theory is that opposite charges are driven apart by the above mechanism and energy is stored in the electric field between them. Cloud electrification appears to require strong updrafts which carry water droplets upward, Supercooling them to -10 to -20 C. These collide with ice crystals to form a soft ice-water mixture called Graupel . The collisions result in a slight positive charge being transferred to ice crystals, and a slight negative charge to the graupel. Updrafts drive lighter ice crystals upwards, causing the cloud top to accumulate increasing positive charge. The heavier negatively charged graupel falls towards the middle and lower portions of the cloud, building up an increasing negative charge. Charge separation and accumulation continue until the Electrical Potential becomes sufficient to initiate lightning discharges, which occurs when the gathering of positive and negative charges forms a sufficiently strong electric field. There are several additional theories for the origin of charge separation. | |||||||||||||||
| |||||||||||||||
| Date | September 9 , 2004 |
||||||||||||||
| Url | http://wwwnaturecom/news/2004/040906/pf/431120a_pfhtml |
||||||||||||||
|
|
|
|
|
|