LIGHTNING IS A DISCHARGE WITH NEGATIVE ELECTRICAL RESISTANCE

LIGHTNING IS A DISCHARGE WITH NEGATIVE ELECTRICAL RESISTANCE

(November 2024)

The lightning that characterizes thunderstorms is produced by frozen and supercooled liquid precipitation particles in the high altitude thunderclouds (See R.P. Feynman-R.B. Leighton-M. Sands, Modern Physics, vol. 5, p. 120. Technical Publishers, 1969. ETO 53 "19" (082), where the authors summarize the physics of lightning in the chapter "Atmospheric Electricity"). The strong upward flow causes water droplets to become supercooled droplets above a temperature of about -7 °C, and then negatively charged ice particles around -20 °C. The droplets freeze first on the outer surface and then on the inside, according to the temperature distribution. The ions in the cloud (mainly H+ and OH- and electrons from water) form domains depending on the temperature distribution. Above about -20 °C, the majority of positive ions are formed, below -20 °C negative ions. The tops of thunderclouds are formed by frozen ice particles. The ions originate from air pollution, friction, solar UV radiation, cosmic radiation, radioactivity...
The empirical distribution of charges in the thundercloud domains: positive charges predominate at the top of the cloud and negative charges at the bottom, probably explained by the 5.5 times greater mobility of electrons. Often a positively charged region also develops in the lowest part of the cloud, at the interface of upflow and downflow.

Charges distribution in thunderclouds

(https://www.researchgate.net/figure/Electric-charges-in-a-cumulonimbus-cloud-and-Intra-cloud-inter-cloud-cloud-to-ground_fig2_266289213)

Voltage differences can occur within a cloud, between a cloud and the Earth, or between two clouds, so lightning can be generated in both vertical and horizontal directions. The lightning travels in and out of the cloud and towards the ground or land objects in a lightning channel with a diameter of one or two mm to a few cms, in which electrons flow towards each other from the cloud and positive ions from the ground object, the currents are called pre-discharge, or pre-flash. There are also special cases.

Pre-discharge with green glow (Upwards streamer emanating from the top of a pool cover,

https://en.wikipedia.org/wiki/Lightning#cite_ref-57)

The white fordischarge emerging from the cloud follows a jagged path towards the Earth, stopping and branching several times for short periods, its shape determined by local conductivity. As it approaches the earth's surface, positive, colourful counter-discharge (corona discharge, ion avalanche, Townsend avalanche, plasma discharge, St. Elmo's fire, glowing embers, cold plasma) from objects or the ground starts to rise upwards towards it. The coloured counter-discharges do not always meet the main electron-forming main discharge above. When a counter-discharge encounters the foreground, a continuous channel is formed between the cloud and the ground. The ion channel initiates a fast, bright main discharge above the breakdown voltage of the air. If the discharge branches off near the ground, a main shower can form on each branch. The current is usually 20-30 000 amperes, but in exceptional cases it can exceed 300 000 amperes. The speed of the lightning flashes is about 60 km/sec and the speed of the main lightning flashes can be up to 180 km/sec. If an ion channel (dark lightning) is created, new lightning flashes are formed on the debris left in the channel after the lightning. The lightning temperature can reach 30,000 Kelvin degrees, and the duration of the main flash is on the order of tenths of a second.
Interesting facts:
The lightning light consists of visible and UV light, but at high currents it can also produce gamma rays and radiate at radio frequencies.

When lightning strikes sandy soil, it produces a glassy substance called fulgurite.

In common parlance, the term 'dry lightning' means when it is not raining when lightning strikes, i.e. the precipitation falling from the cloud does not reach the ground, but the lightning strikes its oncoming counterpart. In dry forests and thickets, dry lightning causes many forest fires.
Dark lightning (R.P. Feynman-R.B. Leighton-M. Sands, p. 134): after a lightning flash, much debris and ion remains in the channel, the next flash passes straight through the old "dark" channel without zigzags.
Lightning (including ball lightning) has a sulphurous, nitrous oxide smell
Atmospheric scientists have found that lightning and invisible discharges, invisible to the camera or the naked eye, emit large amounts of hydroxyl ions
(OH-) and hydroperoxyl ions (HO₂ -), which play an important role in the breakdown of air pollution.

LIGHTNING IS A NEGATIVE-RESISTANCE DISCHARGE

Air dielectric strength greater than 2 x106 V/m. In the absence of an electric field, electrons with an energy of 1 MeV will stop a few metres away, accelerate above it and cause electron avalanches (R.P. Feynman-R.B. Leighton-M. Sands, 133. o), pamatic discharge, corona discharge (also translated as glowing embers, pamatic discharges, ion avalanche, Townsend avalanche, St. Elmo's fire, cold plasma), which form coloured positive ion channels from the surface of the Earth that never reach the clouds. From the clouds, electron channels are launched above the breakdown voltage of air (≈ 21 kV/cm), and if they find a positive ionic channel on the ground, an arc discharge, the lightning bolt, is built.
Arc discharges created in the laboratory are characterised by negative (differential) resistance (https://en.wikipedia.org/wiki/Negative_resistance): the discharge current increases as the voltage that generates the discharge decreases. The current is limited only by the conservation laws.

Discharge voltage decreases → current and temperature increase → degree of ionisation increases (https://en.m.wikipedia.org/wiki/F%C3%A1jl:Voltage_controlled_negative_resistance.svg)

Negative resistance or negative differential resistance refers to a range of currents in which the higher the current, the lower the voltage. From Ohm's law, electrical resistance is the ratio of voltage to current. The principle of conservation of energy precludes the existence of absolute negative resistance, which is why such devices and phenomena operate only by absorbing external energy, e.g. fluorescent tubes:

Glow discharge current voltage curve English.svg

Voltage-current characteristics of electrical discharge (in neon at 1 torr, with two planar electrodes separated by 50 cm).

(https://en.wikipedia.org/wiki/Electric_discharge_in_gases)

A: random pulses by cosmic radiation
B: saturation current
C: avalanche Townsend discharge
D: self-sustained Townsend discharge
E: unstable region: corona discharge (when the voltage decreases, the current increases!)
F: sub-normal glow discharge
G: normal glow discharge
H: abnormal glow discharge
I: unstable region: glow-arc transition
J: electric arc (when the voltage decreases, the current increases!)
K: electric arc

The A-D region is called a dark discharge; there is some ionization, but the current is below 10 microamperes and there is no significant amount of radiation produced.
The F-H region is a region of glow discharge; the plasma emits a faint glow that occupies almost all the volume of the tube; most of the light is emitted by excited neutral atoms.
The I-K region is a region of arc discharge; the plasma is concentrated in a narrow channel along the center of the tube;

a great amount of radiation is produced. (https://en.wikipedia.org/wiki/Electric_discharge_in_gases)

CONCLUSION: In the case of lightning, the glow discharge is associated with the colour flash from the surface, i.e. electron avalanche ionisation. The arc discharge is associated with the electron flow from the clouds, the thermal emission above the breakdown voltage.

Ball lightning (https://www.24h.com.vn/media-24h/bi-an-hien-tuong-set-hon-cuc-hiem-trong-tu-nhien-c762a1479345.html)

An interesting fact: perhaps an explanation can also be obtained for ball lightning (https://videa.hu/videok/tudomany-technika/lefilmezett-gombvillam-para-Ak1xNJku6ZX0v6pi). If a coloured foreshock from the ground surface does not encounter an upper lightning, and if the atmospheric voltage is high enough, thermal emission rarely occurs even for a coloured foreshock from the ground surface (https://en.wikipedia.org/wiki/Thermal_ionization). Thermionic emission, discharge of electrons in gases are widely used in lightening tubes.

When the plasma tube starts to cool, it separates from the ground surface, and conduction and radiative heat losses cause the still hot ions on its surface to recombine. If the recombined molecules were to move away from the surface, there would be a pressure deficit in the plasma, so there is no outflow, no convective cooling, and the tube takes on a spherical shape. So we do not assume a cohesive force field, but the influx of recombining particles from the centre line and then from the centre point due to decreasing temperature (the temperature gradient) holds the sphere together.

The conductivity of fully ionized plasma:

γ_{c} = \frac{1.56 \times 1 0^{- 4} T^{\frac{3}{2}}}{ln (1.23 \times 1 0^{- 4} T^{\frac{3}{2}} n_{e}^{- \frac{1}{2}})} (V / cm)

where, $T$ is the absolute temperature (10-11000 Kelvin); $n_{e}$ is the electron density in the ionized gas dielectric (https://www.sciencedirect.com/topics/physics-and-astronomy/gas-ionization). The collisions between the particles at any degree of the gas ionization are different from those between the fully ionized gas dielectric. The plasma at any ionization degree is composed of cation, anion, electron and neutral molecule (atom). Under the action of the electric field or the gradient of the temperature field, the ions in the plasma will move in the same direction to the electric field or in the direction of temperature decreasing, leading to the diffusion current of charge motion. The theory of Chapman–Cowling theory determines the conductivity of the weak ionization

γ_{w} = 3.34 \times 1 0^{- 12} \frac{α}{S T^{\frac{1}{2}}}

where, $S$ is the cross section area of collision; $T$ is the absolute temperature; $a$ is the ionization degree. In fact, the full ionization and the weak ionization are the two extreme circumstances of the gas ionization, and in general, for any degree of the gas ionization, the conductivity parallel model must be employed

to calculate the conductivity (https://en.wikipedia.org/wiki/Chapman%E2%80%93Enskog_theory).