Electron precipitation

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Electron precipitation (also called energetic electron precipitation or EEP) is an atmospheric phenomenon that occurs when previously trapped electrons enter the Earth's atmosphere, thus creating communications interferences and other disturbances. [1] Electrons trapped by Earth's magnetic field spiral around field lines to form the Van Allen radiation belt. The electrons are from the solar wind and may remain trapped above Earth for an indefinite period of time (in some cases years). When broadband very low frequency (VLF) waves propagate the radiation belts, the electrons exit the radiation belt and "precipitate" (or travel) into the ionosphere (a region of Earth's atmosphere) where the electrons will collide with ions. [2] Electron precipitation is regularly linked to ozone depletion. It is often caused by lightning strikes.

Contents

Process

An electron's gyrofrequency is the number of times it revolves around a field line. [1] VLF waves traveling through the magnetosphere, caused by lightning or powerful transmitters, propagate through the radiation belt. When those VLF waves hit the electrons with the same frequency as an electron's gyrofrequency, the electron exits the radiation belt and "precipitates" (because it will not be able to re-enter the radiation belt) throughout the Earth's atmosphere and ionosphere. [2]

Often, as an electron precipitates, it is directed into the upper atmosphere where it may collide with neutral particles, thus depleting the electron's energy. [3] If an electron makes it through the upper atmosphere, it will continue into the ionosphere. Groups of precipitated electrons can change the shape and conductivity of the ionosphere by colliding with atoms or molecules (usually oxygen or nitrogen based particles [4] ) in the region. [5] When colliding with an atom, the electron strips the atom of its other electrons creating an ion. Collisions with the air molecules also release photons which provide a dim "aurora" effect. [4] Because this occurs at such a high altitude, humans in aircraft are not affected by the radiation. [3]

The ionization process, caused by electron precipitation in the ionosphere, increases its electrical conductivity which in turn brings the bottom of the ionosphere to a lower altitude. [5] When this happens, ozone depletion occurs and certain communications may be disrupted. [1] The lowered altitude of the ionosphere is temporary (unless electron precipitation is steady) while the ions and electrons rapidly react to form neutral particles.

Ozone depletion

Electron precipitation can lead to a substantial, short-term loss of ozone (capping out at around 90%). However, this phenomenon also correlates to some long term ozone depletion as well. [6] Studies have revealed that 60 major electron precipitation events occurred from 2002 to 2012. Different measurement tools (see below) read different ozone depletion averages ranging from 5-90%. However, some of the tools (specifically the ones that reported lower averages) did not take accurate readings or missed a couple of years. Typically, ozone depletion resulting from electron precipitation is more common during the winter season. The largest EEP event from the studies during 2002 to 2012 was recorded in October 2003. This event caused an ozone depletion of up to 92%. It lasted for 15 days and the ozone layer was fully restored a couple of days afterwards. EEP ozone depletion studies are important for monitoring the safety of Earth's environment [7] and variations in the solar cycle. [6]

Types

Electron precipitation can be caused by VLF waves from powerful transmitter based communications and lightning storms. [1]

Lightning-induced Electron Precipitation (LEP)

Lightning-induced electron precipitation (also referred to as LEP) occurs when lightning strikes the Earth. When a bolt of lightning strikes the ground, an electromagnetic pulse (EMP) is released which can hit the trapped electrons in the radiation belt. The electrons are then dislodged and "precipitate" into the Earth's atmosphere. [1] Because the EMP caused by lightning strikes is so powerful and occurs over a large range of spectrums, it is known to cause more electron precipitation than transmitter induced precipitation.

Transmitter-induced Precipitation of Electron Radiation (TIPER)

In order to cause electron precipitation, transmitters must produce very powerful waves with wavelengths from 10 to 100 km. [3] Naval communication arrays often cause transmitter-induced precipitation of electron radiation (TIPER) because powerful waves are needed to communicate through water. These powerful transmitters are operating at almost all times of the day. Occasionally, these waves will have the exact heading and frequency needed to cause an electron to precipitate from the radiation belt.

Measurement Methods

Electron precipitation can be studied by using various tools and methods to calculate its effects on the atmosphere. Scientists use superposed epoch analysis to take into account the strengths and weaknesses of a large set of different measurement methods. They then use that collected data to calculate when an EEP event is taking place and its effects on the atmosphere.

Satellite measurements

In most cases, satellite measurements of electron precipitation are actually measurements of ozone depletion that is then linked to EEP events. [6] The different instruments use a wide variety of methods to calculate ozone levels. While some of the methods may provide significantly inaccurate data, the average of all of the data combined is widely accepted as accurate.

GOMOS

The Global Ozone Monitoring by Occultation of Stars (GOMOS) is a measurement instrument aboard the European satellite Envisat. It measures ozone amounts by using the emitted electromagnetic spectrum from surrounding stars combined with trigonometric calculations in a process called stellar occultation. [6]

SABER

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) is a measurement instrument aboard NASA's Thermal Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite. [8] The instrument measures ozone (and other atmospheric conditions) through an infrared radiometer (with a spectral range from 1.27 μm to 17 μm).

MLS

The Microwave Limb Sounder (MLS), an instrument aboard the Aura satellite, measures microwave emission from the Earth's upper atmosphere. This data can help researchers find the levels of ozone depletion to an accuracy of 35%. [6]

MEPED

The Medium Energy Proton Electron Detector (MEPED) measures electrons in the Earth's radiation belt and can estimate the amount of precipitating electrons in the ionosphere. [6]

Sub-ionospheric Detection

With Sub-ionospheric Detection, a signal is sent from a VLF transmitter through the radiation belt to a VLF receiver on the other end. [3] The VLF signal will cause some electrons to precipitate, thus disturbing the VLF signal before it reaches the VLF receiver on the other end. The VLF receiver measures these disturbances and uses the data to estimate amount of precipitated electrons.

PIPER

PIPER is a Stanford-made photometer specifically designed for capturing the photons emitted when ionization occurs in the ionosphere. [1] Researchers can use this data to detect EEP events and measure the amount of precipitated electrons.

X-rays

X-ray equipment can be used in conjunction with other equipment to measure electron precipitation. [1] Because x-rays are emitted during electron collisions, x-rays found in the ionosphere can be correlated to EEP events.

VLF Remote Sensing

VLF Remote Sensing is a technique of monitoring electron precipitation by monitoring VLF transmissions from the U.S. Navy for "Trumi Events" (large changes of phase and amplitude of the waves). [1] Although this method can monitor electron precipitation, it cannot monitor the ionization of said electrons.

History

James Van Allen from the State University of Iowa with his group, were the first to use vehicles with sensors to study electron fluxes precipitating in the atmosphere with rockoon rockets. The rockets would reach a maximum height of 50 km. The soft radiation detected was later named after Van Allen in 1957. [9]

The next advancement of research of electron precipitation was performed by Winckler with his group from the university of Minnesota. They used balloons that carried detectors into the atmosphere. [9]

Related Research Articles

Ionosphere Ionized part of Earths upper atmosphere

The ionosphere is the ionized part of Earth's upper atmosphere, from about 48 km (30 mi) to 965 km (600 mi) altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.

Van Allen radiation belt Zone of energetic charged particles around the planet Earth

A Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetosphere. Earth has two such belts, and sometimes others may be temporarily created. The belts are named after James Van Allen, who is credited with their discovery. Earth's two main belts extend from an altitude of about 640 to 58,000 km above the surface, in which region radiation levels vary. Most of the particles that form the belts are thought to come from solar wind and other particles by cosmic rays. By trapping the solar wind, the magnetic field deflects those energetic particles and protects the atmosphere from destruction.

High-frequency Active Auroral Research Program US military project to analyze the ionosphere and investigate the potential for developing ionospheric enhancement technology for radio communications and surveillance

The High-frequency Active Auroral Research Program (HAARP) was initiated as an ionospheric research program jointly funded by the U.S. Air Force, the U.S. Navy, the University of Alaska Fairbanks, and the Defense Advanced Research Projects Agency (DARPA). It was designed and built by BAE Advanced Technologies. Its original purpose was to analyze the ionosphere and investigate the potential for developing ionospheric enhancement technology for radio communications and surveillance. As a university-owned facility, HAARP is a high-power, high-frequency transmitter used for study of the ionosphere.

Very low frequency The range 3-30 kHz of the electromagnetic spectrum

Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters. Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.

Whistler (radio)

A whistler is a very low frequency or VLF electromagnetic (radio) wave generated by lightning. Frequencies of terrestrial whistlers are 1 kHz to 30 kHz, with a maximum amplitude usually at 3 kHz to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies, and can be converted to audio using a suitable receiver. They are produced by lightning strikes where the impulse travels along the Earth's magnetic field lines from one hemisphere to the other. They undergo dispersion of several kHz due to the slower velocity of the lower frequencies through the plasma environments of the ionosphere and magnetosphere. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers categorizes them into Pure Note, Diffuse, 2-Hop, and Echo Train types.

Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another, or into various parts of the atmosphere. As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. Understanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for amateur radio communications, international shortwave broadcasters, to designing reliable mobile telephone systems, to radio navigation, to operation of radar systems.

Extremely low frequency The range 3-30 Hz of the electromagnetic spectrum

Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower frequency electromagnetic oscillations are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands.

Mars 96 Failed Mars mission

Mars 96 was a failed Mars mission launched in 1996 to investigate Mars by the Russian Space Forces and not directly related to the Soviet Mars probe program of the same name. After failure of the second fourth-stage burn, the probe assembly re-entered the Earth's atmosphere, breaking up over a 320 km (200 mi) long portion of the Pacific Ocean, Chile, and Bolivia. The Mars 96 spacecraft was based on the Phobos probes launched to Mars in 1988. They were of a new design at the time and both ultimately failed. For the Mars 96 mission the designers believed they had corrected the flaws of the Phobos probes, but the value of their improvements was never demonstrated due to the destruction of the probe during the launch phase.

Atmospheric physics The application of physics to the study of the atmosphere

Within the atmospheric sciences, atmospheric physics is the application of physics to the study of the atmosphere. Atmospheric physicists attempt to model Earth's atmosphere and the atmospheres of the other planets using fluid flow equations, chemical models, radiation budget, and energy transfer processes in the atmosphere. In order to model weather systems, atmospheric physicists employ elements of scattering theory, wave propagation models, cloud physics, statistical mechanics and spatial statistics which are highly mathematical and related to physics. It has close links to meteorology and climatology and also covers the design and construction of instruments for studying the atmosphere and the interpretation of the data they provide, including remote sensing instruments. At the dawn of the space age and the introduction of sounding rockets, aeronomy became a subdiscipline concerning the upper layers of the atmosphere, where dissociation and ionization are important.

Index of meteorology articles Wikipedia index

This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.

The following is a chronology of discoveries concerning the magnetosphere.

Plasmasphere

The plasmasphere, or inner magnetosphere, is a region of the Earth's magnetosphere consisting of low-energy (cool) plasma. It is located above the ionosphere. The outer boundary of the plasmasphere is known as the plasmapause, which is defined by an order of magnitude drop in plasma density. In 1963 American scientist Don Carpenter and Soviet astronomer Konstantin Gringauz proved the plasmasphere and plasmapause's existence from the analysis of very low frequency (VLF) whistler wave data. Traditionally, the plasmasphere has been regarded as a well behaved cold plasma with particle motion dominated entirely by the geomagnetic field and, hence, co-rotating with the Earth.

A sudden ionospheric disturbance (SID) is any one of several ionospheric perturbations, resulting from abnormally high ionization/plasma density in the D region of the ionosphere and caused by a solar flare and/or solar particle event (SPE). The SID results in a sudden increase in radio-wave absorption that is most severe in the upper medium frequency (MF) and lower high frequency (HF) ranges, and as a result often interrupts or interferes with telecommunications systems.

Umran Savaş İnan is a scientist at Koç University and Stanford University in the field of geophysics and very low frequency radio science. He received his PhD from Stanford in 1977 under the tutelage of Robert Helliwell. Since Fall 2009, İnan has been the president of Koç University.

Radio atmospheric signal Broadband electromagnetic impulse

A radio atmospheric signal or sferic is a broadband electromagnetic impulse that occurs as a result of natural atmospheric lightning discharges. Sferics may propagate from their lightning source without major attenuation in the Earth–ionosphere waveguide, and can be received thousands of kilometres from their source. On a time-domain plot, a sferic may appear as a single high-amplitude spike in the time-domain data. On a spectrogram, a sferic appears as a vertical stripe that may extend from a few kHz to several tens of kHz, depending on atmospheric conditions.

The Earth–ionosphere waveguide refers to the phenomenon in which certain radio waves can propagate in the space between the ground and the boundary of the ionosphere. Because the ionosphere contains charged particles, it can behave as a conductor. The earth operates as a ground plane, and the resulting cavity behaves as a large waveguide.

Jicamarca Radio Observatory

The Jicamarca Radio Observatory (JRO) is the equatorial anchor of the Western Hemisphere chain of Incoherent Scatter Radar (ISR) observatories extending from Lima, Peru to Søndre Strømfjord, Greenland. JRO is the premier scientific facility in the world for studying the equatorial ionosphere. The Observatory is about half an hour drive inland (east) from Lima and 10 km from the Central Highway. The magnetic dip angle is about 1°, and varies slightly with altitude and year. The radar can accurately determine the direction of the Earth's magnetic field (B) and can be pointed perpendicular to B at altitudes throughout the ionosphere. The study of the equatorial ionosphere is rapidly becoming a mature field due, in large part, to the contributions made by JRO in radio science.

Greenhouse gas monitoring

Greenhouse gas monitoring is the direct measurement of greenhouse gas emissions and levels. There are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry. Methane and nitrous oxide are measured by other instruments. Greenhouse gases are measured from space such as by the Orbiting Carbon Observatory and networks of ground stations such as the Integrated Carbon Observation System.

FR-1 (satellite) French scientific satellite; the second French satellite

FR-1 was the second French satellite. Planned as the first French satellite, it was launched on 6 December 1965—ten days after the actual first French satellite, Astérix—by an American Scout X-4 rocket from the Western Range at Vandenberg Air Force Base. The scientific satellite studied the composition and structure of the ionosphere, plasmasphere, and magnetosphere by measuring the propagation of very low frequency (VLF) waves and the electron density of plasma in those portions of the Earth's atmosphere. FR-1's VLF receiver operated until 26 August 1968. FR-1 remains in orbit as of November 2020.

Llewelyn Robert Owen Storey is a British physicist and electrical engineer who has worked and lived most of his adult life in France. He is known for his research on the Earth's atmosphere, especially whistlers—very low frequency (VLF) radio waves caused by lightning strikes—and the plasmasphere. He was the first person to prove whistlers are caused by lightning strikes and to deduce the plasmasphere's existence. He was heavily involved in designing scientific instruments for FR-1, a 1965 French-American satellite, and subsequent studies and experiments using data FR-1 collected.

References

  1. 1 2 3 4 5 6 7 8 "Ground Observations of Lightning-Induced Electron Precipitation | Stanford VLF Group". vlf.stanford.edu. Retrieved 2015-10-19.
  2. 1 2 Voss, H. D.; Imhof, W. L.; Walt, M.; Mobilia, J.; Gaines, E. E.; Reagan, J. B.; Inan, U. S.; Helliwell, R. A.; Carpenter, D. L. (1984-12-20). "Lightning-induced electron precipitation". Nature. 312 (5996): 740–742. Bibcode:1984Natur.312..740V. doi:10.1038/312740a0.
  3. 1 2 3 4 "Transmitter-Induced Precipitation of Radiation Belt Electrons | Stanford VLF Group". vlf.stanford.edu. Retrieved 2015-10-21.
  4. 1 2 "It's Raining Electrons!". GeoSpace. Retrieved 2015-10-26.
  5. 1 2 "Monitoring Energetic Electron Precipitation | ABOVE: an Array for Broadband Observations of VLF/ELF Emissions". www.ucalgary.ca. Retrieved 2015-10-21.
  6. 1 2 3 4 5 6 Andersson, M. E.; Verronen, P. T.; Rodger, C. J.; Clilverd, M. A.; Seppälä, A. (2014-10-14). "Missing driver in the Sun–Earth connection from energetic electron precipitation impacts mesospheric ozone". Nature Communications. 5: 5197. Bibcode:2014NatCo...5.5197A. doi:10.1038/ncomms6197. PMC   4214406 . PMID   25312693.
  7. ↑ "Ozone Depletion Information, Ozone Depletion Facts, Ozone Layer, Ozone Hole - National Geographic". National Geographic. Retrieved 2015-10-26.
  8. ↑ "SABER - Sounding of the Atmosphere using Broadband Emission Radiometry". saber.gats-inc.com. Retrieved 2015-11-01.
  9. 1 2 "1966SSRv....5..311B Page 311". Bibcode:1966SSRv....5..311B.Cite journal requires |journal= (help)
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