Lightning

Lightning also causes thunder, a sound from the shock wave which develops as heated gases in the vicinity of the discharge experience a sudden increase in pressure.

[28] As well as the thermodynamic and dynamic conditions of the atmosphere, aerosol (e.g. dust or smoke) composition is thought to influence the frequency of lightning flashes in a storm.

Thermonuclear explosions, by providing extra material for electrical conduction and a very turbulent localized atmosphere, have been seen triggering lightning flashes within the mushroom cloud.

The main charging area in a thunderstorm occurs in the central part of the storm where air is moving upward rapidly (updraft) and temperatures range from −15 to −25 °C (5 to −13 °F); see Figure 1.

In order for an electrostatic discharge to occur, two preconditions are necessary: first, a sufficiently high potential difference between two regions of space must exist, and second, a high-resistance medium must obstruct the free, unimpeded equalization of the opposite charges.

Also, given the very low probability of lightning striking the same point repeatedly and consistently, scientific inquiry is difficult even in areas of high CG frequency.

[53] The establishment of the ionic channel takes a comparatively long amount of time (hundreds of milliseconds) in comparison to the resulting discharge, which occurs within a few dozen microseconds.

One hypothesis postulates that showers of relativistic electrons are created by cosmic rays and are then accelerated to higher velocities via a process called runaway breakdown.

[60][61][62] As negatively charged leaders approach, increasing the localized electric field strength, grounded objects already experiencing corona discharge will exceed a threshold and form upward streamers.

Electrons accelerate rapidly as a result in a zone beginning at the point of attachment, which expands across the entire leader network at up to one third of the speed of light.

[67] A typical cloud-to-ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 km (3.1 mi) tall, from within the cloud to the ground's surface.

Once the electric current stops flowing, the channel cools and dissipates over tens or hundreds of milliseconds, often disappearing as fragmented patches of glowing gas.

The nearly instantaneous heating during the return stroke causes the air to expand explosively, producing a powerful shock wave which is heard as thunder.

The transient nature of the current within a lightning flash results in several phenomena that need to be addressed in the effective protection of ground-based structures.

Global monitoring indicates that lightning on Earth occurs at an average frequency of approximately 44 (± 5) times per second, equating to nearly 1.4 billion flashes per year.

These factors include ground elevation, latitude, prevailing wind currents, relative humidity, and proximity to warm and cold bodies of water.

This[clarification needed] occurs from both the mixture of warmer and colder air masses, as well as differences in moisture concentrations, and it generally happens at the boundaries between them.

The flow of warm ocean currents past drier land masses, such as the Gulf Stream, partially explains the elevated frequency of lightning in the Southeast United States.

Because large bodies of water lack the topographic variation that would result in atmospheric mixing, lightning is notably less frequent over the world's oceans than over land.

Freezing, combined with collisions between ice and water, appears to be a critical part of the initial charge development and separation process.

[90] A lightning strike can unleash a variety of effects, some temporary, including very brief emission of light, sound and electromagnetic radiation, and some long-lasting, such as death, damage, and atmospheric and environmental changes.

The discharge by itself is relatively simple short-lived dipole source that creates a single electromagnetic pulse with a duration of about 1 ms and a wide spectral density.

In the absence in the nearby environment of materials with magnetic or electrical interaction properties, at a large distances in a far field zone, the electromagnetic wave will be proportional to the second derivation of the discharge current.

In other cases, the surrounding environment will change the shape of the source signal by absorbing some of its spectrum and converting it into a heat or re-transmitting it back as modified electromagnetic waves.

Wilson,[104] but no evidence was found until 2001/2002,[105][106][107] when researchers at the New Mexico Institute of Mining and Technology detected X-ray emissions from an induced lightning strike along a grounded wire trailed behind a rocket shot into a storm cloud.

[108][109] A number of observations by space-based telescopes have revealed even higher energy gamma ray emissions, the so-called terrestrial gamma-ray flashes (TGFs).

[110] Recent research has shown that secondary species, produced by these TGFs, such as electrons, positrons, neutrons or protons, can gain energies of up to several tens of MeV.

[153][154][155] However, lightning may also improve air quality and clean greenhouse gases such as methane from the atmosphere, while creating nitrogen oxide and ozone at the same time.

[161] The ancient Etruscans produced guides to brontoscopic and fulgural divination of the future based on the omens supposedly displayed by thunder or lightning occurring on particular days of the year or in particular places.

[166][167][168] In French and Italian, the expression for "Love at first sight" is coup de foudre and colpo di fulmine, respectively, which literally translated means "lightning strike".