Theory Lightnings

Thunderstorms are violent weather events, most frequent during summer. Starting at about midday, convection is moving in altitude quantities of moisture which transforms into clouds. Cumulus form first, these typical white, woolpack clouds. They possibly turn further into cumulonimbus, these dark, massive, towering clouds. It's this later form which yields thunderstorms, lightnings, and hail. Cumulonimbus may reach up to more than 8 miles (13 km) in altitude! The flattened aspect of the top of high cumulonimbus is the sign of high winds they encounter by the end of the troposphere and the tropopause. At any given moment about 2,000 thunderstorms roll over Earth, producing some 50 flashes of lightning every second. Lightning emits a broad range of very low frequency (VLF) radio waves, often heard as pop-and-crackle static when listening to AM radio

click the thumbnail to a map of lightnings' distibution worldwide. picture NASA/MSFC

Particles and raindrops motion inside the thunderclouds is creating large volumes of positive and negative electrical charges, by rubbing. It's the discharges of electricity between such masses, and between the clouds and the ground, which are showing up like flashes of lightning. A lightning is an extremely powerful electrical phenomenon, with the temperature reaching up to 60,000° F (33,000 ° C). Most lightning takes place within or between clouds. Only about one-third of all discharges actually strike the ground. When they do, this is a thunderbolt strike, when the electrical power being delivered to whatever or whoever is lying where it falls! Lightnings are accompanied with thunderclaps. Lightnings most commonly occurs in thunderstorms, but it also can occur in snowstorms, sandstorms, and in the ejected material over volcanoes. Lightnings are also a important factor to elevate swiftly short-lived particles in the upper troposphere as they are also producers of ozone

The most advanced science about lightnings is that their are multi-stroke. Cloud-to-ground lightnings actually strike the ground in two or more places. The average number is 1.45, with each strike separated from the previous by tens of meters (yards) or more, and occurring in a matter of fractions of second. The percentage is that a lightning strikes more than one place a third of the time. Hence the chances of being struck by lightning are 45 percent higher than usually thought, as the cone of strike points becomes extended . Generally, the National Severe Storms Laboratory has elevated its criteria and recommends that a safe distance from a previous flash is at least 6-8 mi (10-13 km) as opposed to the previous 2-3 mi (3-5 km). Such multi-stroke lightnings have either separate and distinct channels (or "paths") since the cloud (23 percent), or they fork between the cloud and the ground (10 percent). 3 percent are exhibiting both types of behavior. 67 percent of the new strike points are produced by the second strike in the flash rather than by the third or fourth. These ones usually follow the same path than the second strike

->Recentest studies from satellites in 2006 have found that the regions on Earth experiencing the most intense thunderstorms are found East of the Andes Mountains, in Argentina (where warm and humid air often collides with cooler, drier, one, in a similar way to what is seen East of the Rockies in the US). Some semi-arid regions have powerful storms too, like the southern fringes of the Sahara desert, northern Australia and parts of the Indian subcontinent. Northern Pakistan, Bangladesh, and parts of Central Africa also are on the list of intense thunderstorms. The studies found that it's not where the rainfall are the heaviest that powerful thunderstorms are observed

Since 2001 meteorologists discovered bolts of lightning shooting upwards from the clouds, as they call those lightnings 'gigantic jets'. 10 gigantic jets have been observed since, as they are essentially the same in physics, as usual thunderbolts. Gigantic jets are going upwards until they are reaching the ionized, electrically charged ionosphere, where they are halted! That electric charge there is equalized and spread by that layer of our atmosphere. 'Sprites' and 'elves' are other lightning-related phenomenons as they occurred at altitudes of about 50 miles (80 km), they are reddish and last in the order of 10 milliseconds only. Sprites are jellyfish-shaped as elves are ring-shaped halos. Both occur due to that positively charged lightning (accounting for 10 percent of all thunderbolts striking ground) are draining clouds from their positive charge. When clouds turn negative, another electric field is building up from there to the ionosphere, yielding those electrical phenomenons. That might have some impact as sprites and elves might create a connection between the upper and lower atmosphere. Such visual phenomena are called transient luminous events (TLEs). By 2014, scientists found that sprites form at irregularities in the plasma, or charged particles of gas, in the ionosphere as such irregularities in the plasma are still of a unknown origin. Sprites indeed are a cold plasma phenomenon without the extremely hot temperatures of lightning, like the discharge of a fluorescent tube and they are thought to occur during most large thunderstorm events. Such events are likely due to that lightnings behave like a powerful antenna emitting electromagnetic waves at all frequencies. Those are propagating up into the ionosphere a very electrically conductive medium as solar ultraviolet radiation strips electrons from water molecules. Since 1994, lightnings are suspects of triggering so-called terrestrial gamma-ray flashes or TGFs, at about 500 a day. The link between both however is still ill-decided as lightnings are ten times too weak to generate gamma rays. TGFs form when powerful electric fields course through the atmosphere, just before a lightning bolt travels along the same path. Charged electrical particles interact with the atmosphere to produce those. Blue jets -- a discharge from cloud tops upward into the stratosphere -- and pixies also occur above thunderstorms as all those phenomenons might be linked to cloud turrets, which are cloud pillars extending into the upper atmosphere. Lightning and thunderclouds however are considered natural particle accelerators, triggering avalanches of relativistic runaway electrons, which develop in electric fields within and emit gamma-rays. The energy of those is sufficiently high to yield atmospheric photonuclear reactions that produce neutrons and eventually positrons

During summer and by any thunderstom-prone weather, swimmers, picnickers, and others should always keep an eye on the sky and stay safe during outdoor activities. In the USA, an average of 80 people are killed and 300 injured by lightning each year, and thousands of dollars' worth of property is damaged or destroyed. Extreme heat and flooding only are superseding thunderstorms in terms of weather-related deaths. for more about lightning safety, see National Weather Service Lightning Safety at the NOAA