When the cosmic rays arrive near the
earth, they hit the nuclei of the atoms of the atmosphere, in particular
nitrogen and oxygen, producing secondary particles. The first interaction of
the cosmic ray primary takes place in the top of the atmosphere (Clay et al,
1997). The interaction
The interaction of cosmic ray with the
atmosphere produces particles like kaons, and 𝛾- particles.
The
secondary particles,
like protons, neutrons and photons interact very frequently with the atoms of
the atmosphere giving rise to a cascade of less and less energetic secondary
particles called “air shower”. These cosmic ray showers are produced by a high
energetic proton. The number of particles created in an air shower event can
reach in the billions, depending on the energy and chemical environment (i.e.
atmosphere condition) of the primary particles (Multhauf, 2002).
The main mechanism of energy loss of
high energetic hadrons consists in the disintegration of the molecules of the
atmosphere. This leads to the creation of the new particles through nuclear
interactions. At lower energies, dissipative processes become dominant, in
which the molecules of the atmosphere get either ionized or excited. The most
relevant process of this kind in the case of heavy charged particles is the
ionization of the molecules of the atmosphere. Lighter charged particles like
electrons and positrons lose their energies not only by ionizations, but also
by bremsstrahlung. This consists in the radioactive loss of energy of charged
particles moving inside nuclei of the surrounding molecules (James, 1998).
The total number of secondary
particles within the shower grows rapidly, mainly sustained by the processes of
bremsstrahlung and pair production due to electrons, positrons and photons.
Secondary particles like protons and, to a less extent, neutrons, are easily
stopped by the atmosphere, so that they increase relevantly the number of
particles by disintegrating the molecules of air only during the first stages
of the formation of the shower. The decays of the secondary particles produce
pions which produce mouns and photons of considerable energies. The mouns are
very penetrating particles and do not interact very much with the air (NWS,
2007). They lose a small fraction of their energy before reaching the ground by
ionizing the molecules of the atmosphere. The photons give rise to
electron-positron pair e⁺ e⁻. In turn,
electrons and positrons create other electrons by ionization or other photons
due to bremsstrahlung. In this way, while the cascade propagates inside the
atmosphere, the number of its electrons, positrons and photons grow almost
exponentially (Murugeshan and Kiruthiga, 1984).
If the energy of the primary
particles is below 10¹⁴eV, essentially only the penetrating
mouns and neutrines are able to the sea level, while the other particles in the
cascade are absorbed at higher altitudes. When the primary particles are above
10¹⁴eV, the cascade of secondary particles
arrives to the ground before being stopped by the atmosphere creating an air
shower (Ferrari and Szuszkiewicz, 2006; Anchordoqui, 2003).
The collisions
of cosmic rays in the atmosphere lead to the formation of a stream of lighter particles known as air shower. These
cosmic rays ionize the atmosphere which causes the accumulation of charges in
the thundercloud. This accumulation of charged particles and the relative motion of water droplets and ice particles
within a thundercloud lead to charge seperation, thereby producing lightning (Collier et al,
2006).
Cosmic rays
have been implicated in the trigger of electrical breakdown in lightning. It
has been proposed that essentially all lightning is triggered through a
relativistic process, “runaway breakdown” caused by cosmic ray secondaries
(Schwarzschild, 2008).In a nutshell, cosmic rays
influences the production of new aerosol particles in the troposphere, which
may grow and eventually increase the number of cloud condensation nuclei (Okike
and Collier, 2011). Investigation showed that Galactic Cosmic Ray (GCR) intensity
modulation also influences thundercloud electricity and lightning activities
(Stozhkov, 2003).
Galactic cosmic rays have extremely high energy (1018 eV) (Shibata
et al, 2010). Due to these high energies, they must have originated from a very
energetic process. These cosmic rays exert much influence on the Earth’s
atmosphere since many atmospheric processes (e.g. atmospheric electric current,
cloud and thundercloud formation, concentration of heavy and light ion) are
defined by their electrical properties (Harrison and Stephenson , 2006).
At certain altitudes, cosmic rays
are believed to be a source of atmospheric ionization and could be responsible
for electrical conductivity of the atmosphere at lower altitudes. It has been
reported that ion production rate in the atmosphere and cosmic ray intensity
variations could account for atmospheric current and lightning occurrence at
middle latitudes. Wilson, (1924) suggested that thunderstorm electric field
could accelerate cosmic ray secondary electrons to high energies (Wilson,
1924). The showers of energetic particles produced by such high energy cosmic
rays could provide a conducting path that initiates lightning. (Gurevich et al,
1999).