Glossary

A

air shower
see cosmic ray cascade

albedo particles
particles reflected or scattered back into space from the atmosphere

asymptotic direction
the direction in interplanetary space in which a cosmic ray particle detected at a given point on the Earth travels when it impinges on the Earth's magnetosphere. More information here.

atomic mass
the number A of nucleons (protons and neutrons) in an atomic nucleus

B

burn out
a permanent and irreversible damage of an electronic circuit by parasitic current flows induced by energetic particles

C

CIR
corotating interaction region

CME
coronal mass ejection

CR
cosmic rays

cascade
see nuclear cascade and cosmic ray cascade

Cherenkov emission
emission generated by an electron in a medium where it propagates faster than light

coronal mass ejection
ejection of gas from the Sun, together with the confining magnetic field. More information here.

corotating interaction region
region in interplanetary space where a fast solar wind stream collides with a slow one, forming a discontinuity and shocks

cosmic ray
energetic particle from the Universe impinging on the Earth

cosmic ray cascade
ensemble of secondary particles produced by collisions of an incident cosmic ray particle with atoms of the Earth's atmosphere. More information here

cosmic ray modulation
variation of the galactic cosmic ray flux at Earth in reaction to changes in the solar magnetic field on time scales of years. More information here.

current sheet
a narrow region in a plasma, where the magnetic field changes abruptly, indicating strong electric currents

cylotron motion
motion of an electrically charged particle in a magnetic field; the orbit of the particle in a uniform magnetic field is a circle in the plane perpendicular to the magnetic field (cyclotron motion or gyration), combined with a motion at constant speed along the field line. More information here.

cyclotron radius
radius of the circular orbit of a charged particle in the plane perpendicular to a uniform magnetic field. More information here.

E

eV
electron Volt (unit of energy: 1 eV = 1.6022x10^-19 J). Units for greater quantities: 1 Mega electron Volt (MeV) = 10⁶ eV, 1 Giga electron Volt (GeV) = 10⁹ eV, 1 Tera electron Volt (TeV) = 10¹² eV. More information here.

energetic particle
charged particle (electron, proton, ion) or neutron whose energy is large compared to the thermal energy of the ambient plasma. More information here.

evaporation nucleon
proton or neutron of a few MeV energy emitted by an excited atomic nucleus that has been hit by an energetic particle. More information here.

F

flare (solar flare)
sudden brightening of solar emissions, especially from the corona (EUV, X-rays, radio) and from the chromosphere (optical and infra red lines, gamma rays, hard X-rays, radio). More information here.

filament
gaseous structure suspended in the solar corona by magnetic fields; it appears dark when viewed in front of the solar disk, and bright when viewed above the solar limb (in this case the feature is called a prominence)

flux of particles
number of particles that travel in one second through a surface of 1 m² or 1 cm²

Forbush decrease
depression of the galactic cosmic ray flux at the Earth by an ICME and its shock. More information here.

G

GCR
galactic cosmic rays

GLE
ground level enhancement

galactic cosmic rays
cosmic rays coming from our Galaxy, as opposed to solar cosmic rays or cosmic rays from extragalactic origins. More information here.

geomagnetic cutoff
the threshold (in rigidity or energy) below which charged particles are prevented by the magnetic field of the Earth from reaching the atmosphere

ground level enhancement
transient increase of the flux of solar cosmic rays detected on Earth.

H

Heliosphere
the domain in interstellar space dominated by the solar wind. More information here.

heliospheric magnetic field
the magnetic field in the Heliosphere, dragged out of the solar corona by the solar wind

I

ICME
interplanetary coronal mass ejection

IGY neutron monitor
standardised neutron monitor developed by Simpson (1958) for the International Geophysical Year. More information here.

interplanetary coronal mass ejection
manifestation of a magnetic structure ejected from the Sun in interplanetary space, as detected by space borne instruments. More information here.

ionisation
stripping of an electron from an atom or ion, by electromagnetic radiation or by a collision with an energetic charged particle

K

knock-on nucleon
fast nucleon expelled from a nucleus hit by an energetic particle (cosmic ray). More information here.

L

Larmor radius
see cyclotron radius

latch-up
anomalous state, produced by an energetic particle, of an electronic device which prevents it from responding to input signals

lead producer
device surrounding the moderator of a neutron monitor, where neutrons are produced through collisions of incoming nucleons with lead nuclei. More information here.

M

MC
magnetic cloud

magnetic cloud
magnetic flux rope expelled from the Sun, observed near the Earth about two to five days after its expulsion during a coronal mass ejection. An MC is a special form of an interplanetary coronal mass ejection.

magnetic reconnection
reconfiguration of the magnetic field: a process in a plasma where the connection between two plasma elements changes, leading to the reconfiguration of magnetic structures (corona, magnetosphere of the Earth) and the release of stored energy. More information here.

magnetosphere
region around the Earth (or another planet) dominated by its own magnetic field, thus excluding the solar wind. More information here.

moderator
device surrounding the counter tube of a neutron monitor, where fast neutrons are slowed down through collisions with light particles (hydrogen atoms), to increase the efficiency of their detection by the proportional counter. More information here.

modulation of cosmic rays
variation of the flux of galactic cosmic rays in the Heliosphere, generated by the variation of the heliospheric magnetic field. More information here.

muon
class of elementary particles; they are not permanently present in our environment because they are unstable, but are produced when high energy protons undergo collisions with other nuclei; muons have a positive or negative electric charge. They have longer lifetimes than pions, and can be detected with ground-based instruments.

muon telescope
ground-based cosmic ray detector that measures secondary muons generated by cosmic rays in the Earth's atmosphere. More information here.

N

NM64 neutron monitor
standardised neutron monitor developed by Carmichael (1964). More information here.

neutron monitor
detector of cosmic rays on the Earth, via the secondary particles produced in an air shower. More information here.

nuclear cascade
chain of events where a high-energy particle colliding with an atomic nucleus triggers the emission of secondary particles, which can themselves generate further nuclear reactions. More information here.

P

Parker spiral
shape of the heliospheric magnetic field lines in E. Parker's solar wind model (1958). The field lines are Archimedean spirals, by which the Earth is connected to a region in the western solar hemisphere. The exact connection depends on the solar wind speed. More information here.

particle flux
see flux

photosphere
visible layer of the Sun (or other stars)

pion
class of elementary particles; they are not permanently present in our environment because they are unstable, but are produced when high energy protons undergo collisions with other nuclei; pions may be neutral or have a positive or negative electric charge.

polar cap absorption (PCA)
enhanced absorption of low-frequency electromagnetic waves in the polar ionosphere, due to the enhanced ionisation by penetrating protons from solar energetic particle events.

positron
elementary particle: antiparticle of the electron, with the same mass, but positive electric charge

proportional counter
particle counter, where incident particles of sufficient energy ionise a gas, whose positive ions and electrons are separated by an applied voltage, and constitute an electric current that can be measured. The key element of a neutron monitor is a proportional counter filled with either BF₃ or ³He. More information here.

R

radiation
term used in various ways: it is most often used for electromagnetic waves, but in the field of cosmic ray physics it designates charged particles impinging on the Earth.

radiation belts
regions in the terrestrial magnetosphere (and magnetospheres of other planets) where charged particles are trapped

reconnection
see magnetic reconnection

reflector
device surrounding the lead producer of a neutron monitor, where neutrons generated in the producer are moderated (slowed down) and reflected towards the counter, while low-energy neutrons produced outside the device are prevented from entering it. More information here.

rigidity (magnetic rigidity)
momentum of a charged particle divided by its electric charge, multiplied by the speed of light; a basic quantity when one considers the motion of a charged particle in a magnetic field, because particles with the same rigidity and the same initial conditions follow the same trajectories in a given magnetic field. More information (with some mathematics) here.

S

SCR
solar cosmic rays

SEE
single event effect

SEP
solar energetic particle

SEU
single event upset

secondary particles (secondaries)
particles produced by collisions of an incident cosmic ray particle with atoms of the Earth's atmosphere. More information here.

SEP events
bursts of energetic particles from the Sun in interplanetary space.

shock wave
discontinuity at the interface between a rapidly moving gas and an obstacle. Examples: Earth's bow shock at the interface between the Magnetosphere and the solar wind; supernova shock at the interface between the expanding supernova ejection and the interstellar medium. More information here.

Sievert
unit measuring the sum of the radiation doses absorbed by the different organs of a human being, weighted by the particle species and the sensitivity of the organ (after Rolf Sievert, Swedish physicist 1896-1966)

single event effect (SEE)
damage to an electronic device due to a single impacting energetic particle

single event upset (SEU)
erroneous command in a computer produced by the impact of a heavy ion

solar cosmic rays
cosmic rays accelerated at the Sun, as opposed to galactic cosmic rays. Solar cosmic rays are the high-energy part of solar energetic particles (SEPs).

solar energetic particle
energetic particle of solar origin observed by particle detectors. The term is often used for positively charged particles (protons, ions), excluding electrons. More information here.

solar corona
tenuous magnetised gas surrounding the Sun. More information here.

solar wind
outflow of charged particles from the solar corona. More information here.

space weather
the ensemble of changing environmental conditions in outer space, in reaction to changing conditions on the Sun. Space weather describes the conditions in space that affect Earth, technological systems and human health.

sunspot
dark region on the solar surface, generated by intense magnetic fields rooted in the solar interior

spectrum
measure of the intensity of electromagnetic radiation as a function of their wavelength or frequency, or of charged particles as a function of their energy, momentum or magnetic rigidity. More information on the spectrum of cosmic rays here.

streamer
extended structure in the solar corona

supernova
collapse of a massive star at the end of its life, when it has no more means to maintain its equilibrium and energy generation through nuclear fusion in its interior. More information here.

synchrotron radiation
radiation emitted by a high energy electron or positron circulating around magnetic field lines

Last updated on 2021-08-06