Acronyms and Glossary
Auroral electrojet index—designed to provide a global, quantitative measure of auroral zone magnetic activity produced by enhanced ionospheric currents flowing below and within the auroral oval. Ideally, it is the total range of deviation, at an instant of time, from quiet day values of the horizontal magnetic field around the auroral oval.
Study of the physics and chemistry of the upper atmosphere, concerned especially with upper-atmospheric composition (for example, nature of constituents, density, and temperature) and chemical reactions.
Advanced Modular Incoherent Scatter Radar—combines a powerful, state-of-the-art incoherent scatter radar with supporting optical and radio instrumentation in a transportable format.
anthropogenic radio emission
Emission of radio-frequency electromagnetic radiation caused or produced by human activity.
Advanced Research and Global Observation Satellite
Periodic global motion of Earth’s atmosphere; also called atmospheric oscillation.
Band of light caused by fast charged particles following Earth’s magnetic lines of force to impinge on the upper atmosphere.
British Antarctic Survey
Canadian Advanced Digital Ionosonde
Canadian Auroral Network for the OPEN (Origins of Plasmas in Earth’s Neighborhood) Program Unified Study
Canadian Array for Real-time Investigations of Magnetic Activity
A device that converts light into electrical current; the digital camera equivalent of film.
co-rotating interaction region in the solar wind
coronal mass ejection
The outermost region of the Sun’s atmosphere, visible as a white halo during a solar eclipse.
A telescope, or an attachment for a telescope, equipped with a disk that blocks out most of the Sun to enable photographing of the Sun’s corona.
distributed arrays of small instruments
D, E, F region
Ionospheric ionization appears in a number of regions or layers, with the D layer situated mainly below 80 km altitude, the E layer centered near 110 km, and the F layer having a peak density near 250 km and extending to above 1000 km.
Pattern produced when waves interfere with each other after having been spread or bent as they pass round the edge of an object or through an opening that is close to the wavelength of the waves.
An ion carrying both a positive and a negative charge.
Department of Defense
Department of Energy
Frequency spreading that occurs in single-frequency radiation when the radiating atoms, molecules, or nuclei do not all have the same velocity and may each give rise to a different Doppler shift.
The amount of the change in the observed frequency of a wave due to the relative motion of the source and the observer.
An index of magnetic activity derived from a network of near-equatorial geomagnetic observatories that measures the intensity of the globally symmetrical equatorial electrojet (the ring current).
A process in the ionosphere in which winds and the resultant movement of ionization in the geomagnetic field give rise to induced current.
The intersection plane of Earth’s orbit with the celestial sphere, along which the Sun appears to move as viewed from Earth.
An electric or magnetic field, or a combination of the two, as in an electromagnetic wave.
An electric field spreading in wavelike-fashion through space at a speed of about 300,000 km/s.
A region of high electron concentration in the tropical ionosphere on either side of the equator at magnetic latitudes of about 10 to 20 degrees.
An optical instrument used to make extremely fine spectral resolution measurements.
Rotation of polarization of a beam of linearly polarized light when it passes through matter in the direction of an applied magnetic field.
Galactic cosmic ray—high-energy protons, anti-protons, electrons, positrons, and charged atomic nuclei that originate outside our solar system, most likely (although their origin is unknown) in supernova explosions and/or stellar fusion processes.
The outermost part of Earth’s atmosphere that emits Lyman-alpha radiation under the action of sunlight.
The geologic science of the size and shape of Earth.
A large-scale manifestation of solar wind-magnetosphere-ionosphere coupling that develops when the coupling is intensified by solar wind disturbances such as co-rotating interaction regions (CIRs) or coronal mass ejections (CMEs).
The domain of Sun-Earth interactions, including the near-Earth interplanetary medium and Earth’s magnetosphere, ionosphere, and thermosphere (also called the solar-terrestrial environment).
Global Oscillations Network Group
Global Positioning System
A wave in a fluid medium in which restoring forces are provided primarily by buoyancy (that is, gravity) rather than compression.
The spectral line of neutral hydrogen that falls in the red part of the visible spectrum and is convenient for solar observations; universally used for patrol observations of solar flares.
The analysis of wave motions of the solar surface to determine the structure of the Sun’s interior.
The region surrounding the Sun where the solar wind dominates the interstellar medium.
A series of light and dark bands produced by interference of light waves.
An isolated electron or positron or an atom or molecule that by loss or gain of one or more electrons has acquired a net electric charge.
A graph of the virtual height of the ionosphere plotted against frequency.
A radar system for determining the vertical height at which the ionosphere reflects signals back to Earth at various frequencies.
The region of the atmosphere from approximately 100 to 1000 km in altitude that contains a significant concentration of electrons and ions produced by the ionizing action of the Sun’s radiation (ultraviolet and X rays) on atmospheric particles.
Interplanetary scintillation—rapid variation in apparent position, brightness, or color of a distant luminous object viewed through the atmosphere or ionosphere.
incoherent scatter radar
A 3-hourly planetary index of geomagnetic activity calculated by the Institut für Geophysik der Universität Göttingen, Germany, from the K indices observed at 13 stations primarily in the Northern Hemisphere.
Low-power magnetometer—a single-battery, non-solar unit designed to last for 1 year (or more) of operation in a polar winter environment.
Magnetometer Array for Cusp and Cleft Studies
A measure of the quantity of magnetism, in terms of how densely packed are the magnetic lines of force passing through a specified area in a magnetic field.
A disturbance or fluctuation in Earth’s magnetic field, associated with solar flares; also called geomagnetic storm.
A descriptive term for the changes over typically 1 to 3 hours in the local magnetic field, at high latitudes, as a result of input from the solar wind and current flows in the magnetotail region of Earth’s magnetosphere; can cause geomagnetic induced current at high latitudes.
An instrument for measuring the magnitude and sometimes also the direction of a magnetic field, such as Earth’s magnetic field.
The boundary of the magnetosphere, separating plasma attached to Earth from the one flowing with the solar wind. The location of the magnetopause is determined by where Earth’s magnetic field balances the pressure of the solar wind—about 63,000 km from Earth in the direction of the Sun, or about 1/6th the distance to the Moon’s orbit.
The region around Earth whose processes are dominated by the Earth’s magnetic field, bounded by the magnetopause.
The period from roughly 1645 to 1715 A.D. when sunspots became exceedingly rare, as noted by solar observers of the time.
Unit of frequency, equal to 1 million cycles per second
Great circle that passes through both the north and south poles; also called line of longitude.
Top of the mesosphere situated at about 80 to 85 km.
A division of Earth’s atmosphere extending from altitudes ranging from 30-50 km to 80-90 km.
One million electron volts
Wave in a compressible, electrically conducting fluid immersed in a magnetic field.
National Aeronautics and Space Administration
The line that separates longitudinal magnetic fields of opposite polarity.
National Oceanic and Atmospheric Administration
National Science Foundation
Polar Experimental Network for Geophysical Upper-atmosphere Investigations
The measurement of light intensities.
The visible surface of the Sun.
A wave that is far enough from its source that its wavefront has no effective curvature, or is planar, over a short distance. Seismic and electromagnetic waves are treated as plane waves even though that assumption is not strictly correct.
Large-scale wave, generally associated with the jet stream, that propagates vertically, affecting circulation in the stratosphere. Four or five planetary waves are generally spanning the circumference of Earth at one time.
A gas containing freely moving ions and electrons, which is therefore capable of conducting electric currents. A “partially ionized plasma” such as Earth’s ionosphere is one that also contains neutral atoms.
Outer periphery of the plasmasphere.
Inside Earth’s magnetosphere, a donut-shaped region that is basically an extension of the ionosphere, or the topmost part of Earth’s atmosphere.
Orientation of the vibration pattern of light waves in a singular plane.
An eruption of gas from the lower atmosphere (chromosphere) of a star and visible as part of the inner corona during a total solar eclipse. These eruptions occur above the Sun’s surface (photosphere), where gases are suspended in a loop, apparently by magnetic forces that arch upward into the solar corona and then return to the surface.
Quasi-stellar object, believed to be among the most distant objects in the observable universe, emitting more energy than some of the most powerful galaxies.
radio Luxembourg effect
Powerful transmitters, such as the medium-wave (208 m) 1.2-gigawatt transmitter of Radio-Tele Luxembourg, can heat the ionosphere, causing two effects: first, weaker radio signals that also reflect from the ionosphere become modulated with the stronger signal; second, the ionosphere reflects the radio waves differently, causing the received signal to fade in and out. Also known as ionospheric cross-modulation.
rarefied density region
The upper atmosphere, sometimes defined as the region above the mesosphere, which extends to approximately 50 miles.
An optical radar that can probe the upper atmosphere by collecting light from the bulk medium.
An electric current carried by charged particles trapped in a planet’s magnetosphere. It is caused by the longitudinal drift of energetic (10-200 keV) particles. Earth’s ring current is responsible for geomagnetic storms.
A specially designed radio receiver for continuous monitoring of the intensity of cosmic noise. (Derived from relative ionospheric opacity meter.)
Radiative Inputs from the Sun to Earth
Subauroral polarization streams—an inclusive name for phenomena that play critical roles in energizing and transporting ring current ions as well as convecting thermal plasma in the inner magnetosphere and in the mid- to low-latitude ionosphere.
The approximately 11-year quasi-periodic variation in frequency or number of solar active events.
solar energetic particles
Electrons and atomic nuclei produced in association with solar flares and other dynamic processes tied to the Sun.
A sudden brightening in some part of the Sun, followed by the emission of jets of gas and a flood of ultraviolet radiation. The gale of protons that accompanies a flare can be very dangerous to astronauts.
The edge of the solar disk.
The outward flux of solar particles and magnetic fields from the Sun, typically with velocities close to 350 km/s.
A device that separates light by wavelengths to produce a spectrum.
Any of the relatively cool dark spots appearing periodically in groups on the surface of the Sun that are associated with strong magnetic fields.
A coherent HF radar network of nearly identical, largely automated HF radars that observes scatter of plasma irregularities in the E and F regions.
total electron content
The system for radioing information, including instrument readings and recordings, from a space vehicle to the ground.
Time History of Events and Macroscale Interactions during Substorms. Themis is also the Goddess of Justice, and her blindfolded impartiality is needed in the discussion of substorm theories. Thus this program name has a double meaning, as the goal of the THEMIS mission is to impartially distinguish between two disparate phenomenological and plasma-physical models of the substorm onset mechanism.
The Earth atmosphere between 120 and 250 to 400 km (depending on the solar and geomagnetic activity levels), where temperature increases exponentially up to a limiting value Texo at the thermopause. The temperature Texo is called the exospheric temperature.
Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics
tomographic restoration techniques
Mathematical transforms that combine two-dimensional images and create a three-dimensional composite image.
Temporary penetration of dawn-dusk electric field in times of increasing convection.
very high frequency