How do Thunderstorms Work? 雷电的产生及其机理
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Thanks to Mr. Chris Smith and his website: thenakedscientists.com
The Science of Thunder and Lightning
[Translated by Hanchengxi ]
At any one time, all around the world, there are 2,000 thunderstorms happening, producing over a 100 lightning strikes a second. That's over 8 million lightning bolts every day unleashing the power of 2 milliontons ofTNT. But how do clouds come by all this energy, and couldn't we put it to good use?
But it was a daring experiment by Benjamin Franklin in 1752, and one which he was lucky to survive, that proved it once and for all. Franklin flew a kite into a thunder cloud and was rewarded with a stream of sparks flowing from the bottom of the kite string.
How is lightning generated?
Franklin's experiment worked because lightning is a multi-million volt electrical discharge between one cloud and another, or between a cloud and the Earth. It'sproduced when friction between tiny water and ice particles in clouds,called "hydrometeors", generates static electricity. For reasons that scientists don't fully understand, the smaller particles pick up apositive charge, and the larger particles pick up a negative charge.
As these hydrometeors jostle about, updrafts push the smaller positively-charged particles towards the top of the cloud, leaving the negative charges concentrated at the bottom. It'spossible that the solar wind, a million mile an hour maelstrom of cosmic radiation streaming out of the sun, may help in this sorting process.
Before long the cloud accumulates a massive potential difference measured inmillions of volts. This electrical potential creates a powerful electric field, a bit like the contour lines on a map, which stretchesfrom the bottom of the cloud to the ground (Earth). As a result theground becomes positively charged as electrons are repelled away by thenegative charge in the clouds. Tall and sharp objects, like buildings,trees, lightning conductors, and even golfing umbrellas, deform the contour lines of the field and push them close together, concentrating the electric field around the top of the object and making it a target for a strike. This happens when the field becomes sufficiently strong to overcome the insulting properties of the air, and the cloud discharges to Earth, producing a lightning bolt.
So how much energy is loitering up there?
Each lightning flash is about 3 miles long but only about a centimetre wide. It discharges about 1-10 billion joules of energy and produces a current of some 30,000 - 50,000 amps, which heats the surrounding air to over 20,000 degrees Celsius, three times hotter than the surface of the sun (6000 degrees Celsius). In fact a single lightning bolt unleashes as much energy as blowing up a ton of TNT. And although it might look like a single flash, a strike is actually made up of between three and twelve individual lightning 'strokes', each lasting only a few thousandths of a second. This is what makes lightning appear to flicker.
And what about thunder ?
The intense heat of the lightning discharge superheats the surrounding air causing it to expand explosively. This creates a compression or 'shock'wave - the thunder - which spreads out through the air in all directions, travelling at about a fifth of a mile per second.
The flash and the thunder clap are produced simultaneously - as any one unlucky enough to have ever got very close to a lightning strike can tell you - but the light from the flash travels much more rapidly(186,000 miles per second) than sound (0.2 miles per second approximately). The light therefore reaches you first, then a short while later (depending upon how far away the storm is), the thunder rolls in.
So with all that energy knocking around up there, surely we could collect enough lightning to power a town ?
Unfortunately not - simple maths shows that this is just not feasible :
100 joules of energy keeps a 100 watt light bulb burning for 1 second. So 1 billion joules of energy (the amount in a modest lightning strike) would keep the same single light-bulb burning for just under 120 days.
Could you power a city on the electricity in a Lightning Bolt…?
The average household uses about 500-1000 kilowatt hours (kWh) per month. 1 kilowatt hour is 1000 Joules per second multiplied by 3600 seconds (the number of seconds in an hour); i.e. 3,600000 Joules.
So, the average household consumes about 500 x 3,600000 = 1.8 billion joules of energy per month. So if you could collect all of the energy contained in one lightning strike it would run just one home for a month. This sounds like good news, but not all of the energy inlightning is available as electricity - in fact probably less than 1% of the energy (10 million joules or so) could be harnessed as electricity because a large amount has already been wasted heating up the air.
Then you have to take into consideration the 'strike frequency' for anygiven area, the cost involved in building a tall tower to work as a lightning collector, and then tackle the problem of how to construct a sufficiently big capacitor to store all of the charge you collect. And who would want to live near a lightning collector? That would be one noisy neighbourhood!
And as to the claim that lightning never strikes twice, a few years back New York's Empire State building was hit 15 times in as many minutes; so you can draw your own conclusions about the validity of that statement.
About the Author
ChrisSmith is a clinical lecturer in virology at Cambridge University and the founder and managing editor of the Naked Scientists
有关雷电的科学知识
译文/韩成锡
世界各地每秒钟大约发生2000次闪电，产生超过100次雷击。这意味着每天产生超过8百万伏特的电压，其能量和2百万吨的TNT炸药相当。然而我们为什么任由云层去引发这些能量，而不让其得到好好利用呢？
闪电是如何产生的？
弗兰克林的试验之所以成功，是因为闪电是一种发生在一朵云和另一朵云之间、或者云和地面之间的能量达数百万伏特的放电现象。这个过程的产生是在当微量的水和冰的颗粒与云相接触时，形成一种“水气凝结体”的物质，此时会产生静电。由于科学家至今尚不甚清楚的某些原因，这种“水气凝结体”中的较小的颗粒会产生正电荷，而较大的颗粒的则会产生负电荷。
当这些水气凝结体相互聚集并发生碰撞时，上升气流会推动带正电荷的较小的颗粒向云层上方移动，剩下带负电荷的较大颗粒，聚集在云层下方。太阳风可能也会对这一过程产生影响：宇宙射线以百万公里每小时的速度由太阳表面辐射冲出，也许促进了这一过程的进行。
此过程之后不久，云层已经聚集了数量众多、数量级在百万伏特的势差。这些电压（势差）产生强大的电场（有些像地图上的等高线），从云层的底端向地面（地球）延伸，结果导致地面变为正电势（正电子受到云层负电子的排斥）。而高和尖锐的物体，例如建筑物、树木、避雷针、甚至是高尔夫球场的遮雨伞，都能够使得电场的等高线发生变形，并将其压缩聚集，产生围绕在物体周围的电场，进而使其成为引发闪电的目标。当电场变得充分强大以致冲破通常情况下绝缘状态的空气时，闪电随即发生，云层向地面放电，产生响彻天地间的青天霹雳。
每个闪电大约有3英里长，但是只有大约1公分宽，释放出10亿到100亿焦耳的能量，其电流达到30000到50000安培。这些能量将周围的空气加热到超过20000摄氏度，超过太阳表面温度（约6000摄氏度）的3倍。实际上，单个闪电所释放的能量大约相当于一吨TNT炸药的能量。虽然看起来只是一闪，却是包含了3到12次的独立闪电，每次持续时间只有一秒钟的千分之几。这也就是为什么闪电看上去总是闪烁数次的原因。
那么什么又是雷呢？
闪电释放出的强大热量使得周围的空气迅速过热、膨胀并爆炸，由此产生了压缩或者“冲击”波——雷——以每秒钟1/5英里的速度向四处扩散。电闪和雷是同时产生的——如果有人很不幸，此时离闪电太近，那么我可以告诉你，闪电的速度那是相当地快（每秒186000英里），比声音的速度（每秒大约0.2英里）快的多了。因此，闪电会首先到达你的身边，之后经过短暂的间歇（取决于你离雷暴中心有多远），雷声便轰隆轰隆地汹涌而来。
那么当如此多的雷电产生时，我们能不能够将之收集起来，作为一个小镇的电力呢？
很不幸，答案是：不能。简单的数学计算将告诉你这如何行不通：
100焦的能量能够维持100瓦的日光灯持续照明1秒钟，因此，10亿焦的能量（大多数闪电产生的能量的数量级）能够维持同样条件下的日光灯持续照明不超过120天，如果镇里有100户人家，就算每户只有一盏日光灯，那么...
那么当集中高频的雷电霹雳来临时，能否供应一个城市的电力呢？
一个中等家庭每月使用的平均电力大约为500-1000千瓦小时(kWh)。1千瓦小时等于1000焦耳/秒乘以3600秒（一小时的秒数），即3600000焦耳。
所以，一个中等家庭每月消耗的能量约为500 x3,600000 =18亿焦耳，如果你能够将闪电中所有的能量收集起来，其仅够维持一个家庭一月的使用。这听上去好像还不错，然而并非闪电中的所有能量都是可用的电力——实际上，低于总能量1%（大约1000万焦耳上下）的电力可以用来发电，其余的大部分则都耗费在加热周围的空气上去了。
然后， 你需要考虑，任意一个地方发生闪电的频率到底有多少？相关费用还包括要建立一个高塔作为闪电收集器，之后你还要处理如何建立一个容量足够大的电容器以储存你所收集到的电力，并且你还得考虑，谁愿意住在这大家伙（闪电收集器）附近？这可是个相当聒噪的邻居！
有一种流传甚广的说话，讲的是任何时候闪电都不会连续两次击中同一目标，大家回想下几年前纽约帝国大厦在15分钟里被击中了15次，你就可以得出自己的结论：刚才那句话，是对，还是不对。
关于作者
克里斯 史密斯是英国剑桥大学滤过性微生物学科的临床讲师，同时也是“无遮蔽科学家”网站的创始人和执行编辑。
[ 本帖最后由 韩成锡 于 2007-7-7 10:52 编辑 ]
The Science of Thunder and Lightning
[Translated by Hanchengxi ]
At any one time, all around the world, there are 2,000 thunderstorms happening, producing over a 100 lightning strikes a second. That's over 8 million lightning bolts every day unleashing the power of 2 milliontons ofTNT. But how do clouds come by all this energy, and couldn't we put it to good use?
Figure 1: At any time there are over 2,000 thunderstorms occurringworldwide, each producing over a 100 lightning strikes a second. Thatsover 8 million lightning bolts every day.
But it was a daring experiment by Benjamin Franklin in 1752, and one which he was lucky to survive, that proved it once and for all. Franklin flew a kite into a thunder cloud and was rewarded with a stream of sparks flowing from the bottom of the kite string.
How is lightning generated?
Franklin's experiment worked because lightning is a multi-million volt electrical discharge between one cloud and another, or between a cloud and the Earth. It'sproduced when friction between tiny water and ice particles in clouds,called "hydrometeors", generates static electricity. For reasons that scientists don't fully understand, the smaller particles pick up apositive charge, and the larger particles pick up a negative charge.
As these hydrometeors jostle about, updrafts push the smaller positively-charged particles towards the top of the cloud, leaving the negative charges concentrated at the bottom. It'spossible that the solar wind, a million mile an hour maelstrom of cosmic radiation streaming out of the sun, may help in this sorting process.
Before long the cloud accumulates a massive potential difference measured inmillions of volts. This electrical potential creates a powerful electric field, a bit like the contour lines on a map, which stretchesfrom the bottom of the cloud to the ground (Earth). As a result theground becomes positively charged as electrons are repelled away by thenegative charge in the clouds. Tall and sharp objects, like buildings,trees, lightning conductors, and even golfing umbrellas, deform the contour lines of the field and push them close together, concentrating the electric field around the top of the object and making it a target for a strike. This happens when the field becomes sufficiently strong to overcome the insulting properties of the air, and the cloud discharges to Earth, producing a lightning bolt.
Figure 2: Each lightning flash is about 3 miles long but only about acentimetre wide. It discharges about 1-10 billion joules of energy andproduces a current of some 30,000 - 50,000 amps, which heats thesurrounding air to over 20,000 degrees Celsius, three times hotter thanthe surface of the sun (6000 degrees Celsius).
So how much energy is loitering up there?
Each lightning flash is about 3 miles long but only about a centimetre wide. It discharges about 1-10 billion joules of energy and produces a current of some 30,000 - 50,000 amps, which heats the surrounding air to over 20,000 degrees Celsius, three times hotter than the surface of the sun (6000 degrees Celsius). In fact a single lightning bolt unleashes as much energy as blowing up a ton of TNT. And although it might look like a single flash, a strike is actually made up of between three and twelve individual lightning 'strokes', each lasting only a few thousandths of a second. This is what makes lightning appear to flicker.
And what about thunder ?
The intense heat of the lightning discharge superheats the surrounding air causing it to expand explosively. This creates a compression or 'shock'wave - the thunder - which spreads out through the air in all directions, travelling at about a fifth of a mile per second.
The flash and the thunder clap are produced simultaneously - as any one unlucky enough to have ever got very close to a lightning strike can tell you - but the light from the flash travels much more rapidly(186,000 miles per second) than sound (0.2 miles per second approximately). The light therefore reaches you first, then a short while later (depending upon how far away the storm is), the thunder rolls in.
So with all that energy knocking around up there, surely we could collect enough lightning to power a town ?
Unfortunately not - simple maths shows that this is just not feasible :
100 joules of energy keeps a 100 watt light bulb burning for 1 second. So 1 billion joules of energy (the amount in a modest lightning strike) would keep the same single light-bulb burning for just under 120 days.
Could you power a city on the electricity in a Lightning Bolt…?
The average household uses about 500-1000 kilowatt hours (kWh) per month. 1 kilowatt hour is 1000 Joules per second multiplied by 3600 seconds (the number of seconds in an hour); i.e. 3,600000 Joules.
So, the average household consumes about 500 x 3,600000 = 1.8 billion joules of energy per month. So if you could collect all of the energy contained in one lightning strike it would run just one home for a month. This sounds like good news, but not all of the energy inlightning is available as electricity - in fact probably less than 1% of the energy (10 million joules or so) could be harnessed as electricity because a large amount has already been wasted heating up the air.
Then you have to take into consideration the 'strike frequency' for anygiven area, the cost involved in building a tall tower to work as a lightning collector, and then tackle the problem of how to construct a sufficiently big capacitor to store all of the charge you collect. And who would want to live near a lightning collector? That would be one noisy neighbourhood!
And as to the claim that lightning never strikes twice, a few years back New York's Empire State building was hit 15 times in as many minutes; so you can draw your own conclusions about the validity of that statement.
About the Author
ChrisSmith is a clinical lecturer in virology at Cambridge University and the founder and managing editor of the Naked Scientists
有关雷电的科学知识
译文/韩成锡
世界各地每秒钟大约发生2000次闪电，产生超过100次雷击。这意味着每天产生超过8百万伏特的电压，其能量和2百万吨的TNT炸药相当。然而我们为什么任由云层去引发这些能量，而不让其得到好好利用呢？
图1 世界各地每秒钟大约发生2000次闪电，产生超过100次雷击。这意味着每天产生超过8百万伏特的电压，其能量和2百万吨的TNT炸药相当。
闪电是如何产生的？
弗兰克林的试验之所以成功，是因为闪电是一种发生在一朵云和另一朵云之间、或者云和地面之间的能量达数百万伏特的放电现象。这个过程的产生是在当微量的水和冰的颗粒与云相接触时，形成一种“水气凝结体”的物质，此时会产生静电。由于科学家至今尚不甚清楚的某些原因，这种“水气凝结体”中的较小的颗粒会产生正电荷，而较大的颗粒的则会产生负电荷。
当这些水气凝结体相互聚集并发生碰撞时，上升气流会推动带正电荷的较小的颗粒向云层上方移动，剩下带负电荷的较大颗粒，聚集在云层下方。太阳风可能也会对这一过程产生影响：宇宙射线以百万公里每小时的速度由太阳表面辐射冲出，也许促进了这一过程的进行。
此过程之后不久，云层已经聚集了数量众多、数量级在百万伏特的势差。这些电压（势差）产生强大的电场（有些像地图上的等高线），从云层的底端向地面（地球）延伸，结果导致地面变为正电势（正电子受到云层负电子的排斥）。而高和尖锐的物体，例如建筑物、树木、避雷针、甚至是高尔夫球场的遮雨伞，都能够使得电场的等高线发生变形，并将其压缩聚集，产生围绕在物体周围的电场，进而使其成为引发闪电的目标。当电场变得充分强大以致冲破通常情况下绝缘状态的空气时，闪电随即发生，云层向地面放电，产生响彻天地间的青天霹雳。
图2 每个闪电大约有3英里长，但是只有大约1公分宽，释放出10亿到100亿焦耳的能量，其电流达到30000到50000安培。这些能量将周围的空气加热到超过20000摄氏度，超过太阳表面温度（约6000摄氏度）的3倍。
每个闪电大约有3英里长，但是只有大约1公分宽，释放出10亿到100亿焦耳的能量，其电流达到30000到50000安培。这些能量将周围的空气加热到超过20000摄氏度，超过太阳表面温度（约6000摄氏度）的3倍。实际上，单个闪电所释放的能量大约相当于一吨TNT炸药的能量。虽然看起来只是一闪，却是包含了3到12次的独立闪电，每次持续时间只有一秒钟的千分之几。这也就是为什么闪电看上去总是闪烁数次的原因。
那么什么又是雷呢？
闪电释放出的强大热量使得周围的空气迅速过热、膨胀并爆炸，由此产生了压缩或者“冲击”波——雷——以每秒钟1/5英里的速度向四处扩散。电闪和雷是同时产生的——如果有人很不幸，此时离闪电太近，那么我可以告诉你，闪电的速度那是相当地快（每秒186000英里），比声音的速度（每秒大约0.2英里）快的多了。因此，闪电会首先到达你的身边，之后经过短暂的间歇（取决于你离雷暴中心有多远），雷声便轰隆轰隆地汹涌而来。
那么当如此多的雷电产生时，我们能不能够将之收集起来，作为一个小镇的电力呢？
很不幸，答案是：不能。简单的数学计算将告诉你这如何行不通：
100焦的能量能够维持100瓦的日光灯持续照明1秒钟，因此，10亿焦的能量（大多数闪电产生的能量的数量级）能够维持同样条件下的日光灯持续照明不超过120天，如果镇里有100户人家，就算每户只有一盏日光灯，那么...
那么当集中高频的雷电霹雳来临时，能否供应一个城市的电力呢？
一个中等家庭每月使用的平均电力大约为500-1000千瓦小时(kWh)。1千瓦小时等于1000焦耳/秒乘以3600秒（一小时的秒数），即3600000焦耳。
所以，一个中等家庭每月消耗的能量约为500 x3,600000 =18亿焦耳，如果你能够将闪电中所有的能量收集起来，其仅够维持一个家庭一月的使用。这听上去好像还不错，然而并非闪电中的所有能量都是可用的电力——实际上，低于总能量1%（大约1000万焦耳上下）的电力可以用来发电，其余的大部分则都耗费在加热周围的空气上去了。
然后， 你需要考虑，任意一个地方发生闪电的频率到底有多少？相关费用还包括要建立一个高塔作为闪电收集器，之后你还要处理如何建立一个容量足够大的电容器以储存你所收集到的电力，并且你还得考虑，谁愿意住在这大家伙（闪电收集器）附近？这可是个相当聒噪的邻居！
有一种流传甚广的说话，讲的是任何时候闪电都不会连续两次击中同一目标，大家回想下几年前纽约帝国大厦在15分钟里被击中了15次，你就可以得出自己的结论：刚才那句话，是对，还是不对。
关于作者
克里斯 史密斯是英国剑桥大学滤过性微生物学科的临床讲师，同时也是“无遮蔽科学家”网站的创始人和执行编辑。
[ 本帖最后由 韩成锡 于 2007-7-7 10:52 编辑 ]
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