Solar proton event
Encyclopedia
A Solar proton event occurs when proton
s emitted by the Sun
become accelerated to very high energies either close to the Sun during a solar flare
or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the Earth's magnetic field
and cause ionization in the ionosphere
. The effect is similar to auroral events, the difference being that electron
s and not protons are involved. Energetic solar protons are also a significant radiation
hazard to spacecraft
and astronauts.
, south pole
, and South Atlantic magnetic anomaly
.
Protons are charged particles and are therefore influenced by magnetic fields. When the energetic protons leave the Sun
, they preferentially follow (or are guided by) the Sun's powerful magnetic field. When solar protons enter the domain of the Earth's magnetosphere
where the magnetic fields become stronger than the solar magnetic fields, they are guided by the Earth's magnetic field into the polar regions where the majority of the Earth's magnetic field lines enter and exit.
Energetic protons that are guided into the polar regions collide with atmospheric constituents and release their energy through the process of ionization. The majority of the energy is extinguished in the extreme lower region of the ionosphere (around 50-80 km in altitude). This area is particularly important to ionospheric radio communications
because this is the area where most of the absorption of radio signal energy occurs. The enhanced ionization produced by incoming energetic protons increases the absorption levels in the lower ionosphere and can have the effect of completely blocking all ionospheric radio communications through the polar regions. Such events are known as Polar Cap Absorption events (or PCAs). These events commence and last as long as the energy of incoming protons at approximately greater than 10 MeV (million electron volts) exceeds roughly 10 pfu (pfu = proton flux units = ) at geosynchronous satellite altitudes.
The more severe proton events can be associated with geomagnetic storms that can cause widespread disruption to electrical grid
s. However, proton events themselves are not responsible for producing anomalies in power grids, nor are they responsible for producing geomagnetic storms. Power grids are only sensitive to fluctuations in the Earth's magnetic field.
Extremely intense solar proton flares capable of producing energetic protons with energies in excess of 100 MeV can increase neutron count rates at ground levels through secondary radiation effects. These rare events are known as Ground Level Events (or GLE's).
There is no substantive scientific evidence to suggest that energetic proton events are harmful to human health at ground levels, particularly at latitudes where most of the Earth's population resides. The Earth's magnetic field is exceptionally good at preventing the radiative effects of energetic particles from reaching ground levels. High altitude commercial transpolar aircraft flights have measured increases in radiation during energetic proton events, but a warning system is in place that limits these effects by alerting pilots to lower their cruising altitudes. Aircraft flights away from the polar regions are far less likely to see an impact from solar proton events.
Significant proton radiation exposure can be experienced by astronauts who are outside of the protective shield of the Earth's magnetosphere, such as an astronaut in-transit to, or located on the Moon. However, the effects can be minimized if astronauts are in a low-Earth orbit and remain confined to the most heavily shielded regions of their spacecraft. Proton radiation levels in low earth orbit increase with orbital inclination. Therefore, the closer a spacecraft approaches the polar regions, the greater the exposure to energetic proton radiation will be.
Astronauts have reported seeing flashes or streaks of light as energetic protons interact with their optic tissues. Similar flashes and streaks of light occur when energetic protons strike the sensitive optical electronics in spacecraft (such as star trackers and other cameras). The effect can be so pronounced that during extreme events, it is not possible to obtain quality images of the Sun or stars. This can cause spacecraft to lose their orientation, which is critical if ground controllers are to maintain control.
Energetic proton storms can also electrically charge spacecraft to levels that can damage electronic components. They can also cause electronic components to behave erratically. For example, solid state memory on spacecraft can be altered, which may cause data or software contamination and result in unexpected (phantom) spacecraft commands being executed. Energetic proton storms also destroy the efficiency of the solar panels that are designed to collect and convert sunlight to electricity. During years of exposure to energetic proton activity from the Sun, spacecraft can lose a substantial amount of electrical power that may require important instruments to be turned off.
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s emitted by the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
become accelerated to very high energies either close to the Sun during a solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
and cause ionization in the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
. The effect is similar to auroral events, the difference being that electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s and not protons are involved. Energetic solar protons are also a significant radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
hazard to spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
and astronauts.
Description
Solar protons normally have insufficient energy to penetrate through the Earth's magnetic field. However, during unusually strong solar flare events, protons can be produced with sufficient energies to penetrate deeper into the Earth's magnetosphere and ionosphere. Regions where deeper penetration can occur includes the north poleNorth Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
, south pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
, and South Atlantic magnetic anomaly
South Atlantic Anomaly
The South Atlantic Anomaly is an area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher than usual levels of radiation...
.
Protons are charged particles and are therefore influenced by magnetic fields. When the energetic protons leave the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, they preferentially follow (or are guided by) the Sun's powerful magnetic field. When solar protons enter the domain of the Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
where the magnetic fields become stronger than the solar magnetic fields, they are guided by the Earth's magnetic field into the polar regions where the majority of the Earth's magnetic field lines enter and exit.
Energetic protons that are guided into the polar regions collide with atmospheric constituents and release their energy through the process of ionization. The majority of the energy is extinguished in the extreme lower region of the ionosphere (around 50-80 km in altitude). This area is particularly important to ionospheric radio communications
Radio propagation
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
because this is the area where most of the absorption of radio signal energy occurs. The enhanced ionization produced by incoming energetic protons increases the absorption levels in the lower ionosphere and can have the effect of completely blocking all ionospheric radio communications through the polar regions. Such events are known as Polar Cap Absorption events (or PCAs). These events commence and last as long as the energy of incoming protons at approximately greater than 10 MeV (million electron volts) exceeds roughly 10 pfu (pfu = proton flux units = ) at geosynchronous satellite altitudes.
The more severe proton events can be associated with geomagnetic storms that can cause widespread disruption to electrical grid
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
s. However, proton events themselves are not responsible for producing anomalies in power grids, nor are they responsible for producing geomagnetic storms. Power grids are only sensitive to fluctuations in the Earth's magnetic field.
Extremely intense solar proton flares capable of producing energetic protons with energies in excess of 100 MeV can increase neutron count rates at ground levels through secondary radiation effects. These rare events are known as Ground Level Events (or GLE's).
There is no substantive scientific evidence to suggest that energetic proton events are harmful to human health at ground levels, particularly at latitudes where most of the Earth's population resides. The Earth's magnetic field is exceptionally good at preventing the radiative effects of energetic particles from reaching ground levels. High altitude commercial transpolar aircraft flights have measured increases in radiation during energetic proton events, but a warning system is in place that limits these effects by alerting pilots to lower their cruising altitudes. Aircraft flights away from the polar regions are far less likely to see an impact from solar proton events.
Significant proton radiation exposure can be experienced by astronauts who are outside of the protective shield of the Earth's magnetosphere, such as an astronaut in-transit to, or located on the Moon. However, the effects can be minimized if astronauts are in a low-Earth orbit and remain confined to the most heavily shielded regions of their spacecraft. Proton radiation levels in low earth orbit increase with orbital inclination. Therefore, the closer a spacecraft approaches the polar regions, the greater the exposure to energetic proton radiation will be.
Astronauts have reported seeing flashes or streaks of light as energetic protons interact with their optic tissues. Similar flashes and streaks of light occur when energetic protons strike the sensitive optical electronics in spacecraft (such as star trackers and other cameras). The effect can be so pronounced that during extreme events, it is not possible to obtain quality images of the Sun or stars. This can cause spacecraft to lose their orientation, which is critical if ground controllers are to maintain control.
Energetic proton storms can also electrically charge spacecraft to levels that can damage electronic components. They can also cause electronic components to behave erratically. For example, solid state memory on spacecraft can be altered, which may cause data or software contamination and result in unexpected (phantom) spacecraft commands being executed. Energetic proton storms also destroy the efficiency of the solar panels that are designed to collect and convert sunlight to electricity. During years of exposure to energetic proton activity from the Sun, spacecraft can lose a substantial amount of electrical power that may require important instruments to be turned off.