Under the premises of 1) induced emission of "droplets" of gamma photons and 2) cohesive forces between the photons of such droplets, terrestrial gamma flashes (TGF) and gamma glows from thunder-clouds become much less mysterious.
Different from the case of ultra-high-energy gamma flashes, cohesive forces may not be necessary in the terrestrial case, as the photon-droplets could emerge as very narrow beams, and distance from source to detector (leading to beam-width expansion) is relatively small.
For better understanding here some quotes from Positron clouds within thunderstorms
Lightning leaders have been observed to emit bright sub-microsecond pulses of x-rays with energies typically in the few hundred keV range.
Long laboratory sparks have been shown to produce similar x-ray emissions.
Thunderstorms produce bright sub-millisecond bursts of gamma rays, called terrestrial gamma ray flashes (TGFs), with energies reaching several tens of MeV.
For both the lightning/laboratory spark emissions and TGFs, the x-rays and gamma rays are produced by bremsstrahlung interactions of energetic electrons with air. However, it is a theoretical challenge to explain how so many high-energy electrons are generated in our atmosphere on such short time scales.
Another kind of emission from thunderclouds is the gamma-ray glow. Gamma-ray glows appear as sub-second to minute long emissions of gamma rays. Like TGFs, the glows are produced by bremsstrahlung emissions from energetic electrons and in some cases have been found to have spectra similar to those of TGFs. However, glows last much longer than TGFs and have much lower fluxes. Gamma-ray glows have been observed by aircraft, balloon and on the ground.
… demonstrated that active thunderstorms produce gamma rays that last tens of seconds, with energies greater than 110 keV.
They found that the gamma-ray emissions were generally terminated, rather than caused, by lightning.
In a series of balloon flights, … flew scintillators and electric field sensors through and above active thunderstorms and measured gamma-ray glows of up to 120 keV in energy. They found that the gamma-ray emissions occurred at an altitude of 4 km where the electric field was highest.
The emission persisted while the balloon passed through the strong-electric-field region within the storm, except that it terminated and then restarted following two lightning flashes.
… measured gamma-ray enhancements of up to 70 times the local background level at the Monju nuclear reactor in Japan during a winter thunderstorm.
The currently prevailing explanation is Relativistic Runaway Electron Avalanche
is an apriori highly unlikely explanation: Electrons are assumed to at first accelerate to relativistic speeds (i.e. with Lorentz-factors substantially higher than 1); then gamma photons (x-rays) are "produced by bremsstrahlung interactions of energetic electrons with air
". Whereas normally losses due to friction resp. bremsstrahlung increase with electron speed, the hypothesis is based on substantially decreasing friction losses with increasing speed
Two quotes from Lightning
A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 kilometers tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process.
The cause of the X-ray emissions is still a matter for research, as the temperature of lightning is too low to account for the X-rays observed.
Two quotes from Lightning strike
Most of the early formative and propagation stages are much dimmer and not visible to the human eye.
The establishment of the ionic channel takes a comparatively long amount of time (hundreds of milliseconds) in comparison to resulting discharge which occurs within a few microseconds.
The explanation of terrestrial gamma glows and flashes by photon cohesion is very simple. The plasma channels of thunderclouds act like a gamma-laser ("gaser") gain medium; and a flash "particle" consists not of one single gamma quantum but of a compound of gamma photons.
The energy of individual photons of such gamma droplets primarily stems from ionization energies
in the plasma channels of the thunderclouds.
The longer a spontaneously emitted gamma quantum propagates within an ionic channel, the bigger a droplet can grow due to induced emission of coherent photons. A gamma flash with an "energy spectrum" of around 500 keV could therefore be composed not of one quantum but e.g. of around 10,000 quanta of each 50 eV. As the wavelength of a 50 eV photon is only around 2.5 x 10-8
m, and 40 x 40 x 40 = 64,000 cubes of edge length 2.5 x 10-8
m can form a cube with an edge length of 1 micrometer, such a composite gamma droplet can be very compact.
No sophisticated feedback mechanism is necessary to explain repetitive glows and flashed from the same thundercloud regions.
Another relevant quote from Wikipedia
In a few situations it is possible to obtain lasing with only a single pass of EM radiation through the gain medium, and this produces a laser beam without any need for a resonant or reflective cavity (see for example nitrogen laser). Thus, reflection in a resonant cavity is usually required for a laser, but is not absolutely necessary.
At least in the case of "long laboratory sparks
", a simple experiment should be able to refute the currently prevailing Relativistic Runaway Electron Avalanche
hypothesis: The application of a magnetic field preventing the electrons by the Lorentz force from simply accelerating in the electrostatic field.
The solution of the mystery of terrestrial and extraterrestrial gamma glows and flashes: photon cohesion