D
Acronyms and Glossary
AE index
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.
Aeronomy
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.
AMISR
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.
ARGOS
Advanced Research and Global Observation Satellite
atmospheric tide
Periodic global motion of Earth’s atmosphere; also called atmospheric oscillation.
aurora
Band of light caused by fast charged particles following Earth’s magnetic lines of force to impinge on the upper atmosphere.
BAS
British Antarctic Survey
CADI
Canadian Advanced Digital Ionosonde
CANOPUS
Canadian Auroral Network for the OPEN (Origins of Plasmas in Earth’s Neighborhood) Program Unified Study
CARISMA
Canadian Array for Real-time Investigations of Magnetic Activity
charge-coupled device
A device that converts light into electrical current; the digital camera equivalent of film.
CIR
co-rotating interaction region in the solar wind
CME
coronal mass ejection
corona
The outermost region of the Sun’s atmosphere, visible as a white halo during a solar eclipse.
coronograph
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.
DASI
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.
diffraction pattern
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.
dipolar ion
An ion carrying both a positive and a negative charge.
DOD
Department of Defense
DOE
Department of Energy
Doppler broadening
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.
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.
Dst index
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).
dynamo effect
A process in the ionosphere in which winds and the resultant movement of ionization in the geomagnetic field give rise to induced current.
ecliptic plane
The intersection plane of Earth’s orbit with the celestial sphere, along which the Sun appears to move as viewed from Earth.
electromagnetic field
An electric or magnetic field, or a combination of the two, as in an electromagnetic wave.
electromagnetic wave
An electric field spreading in wavelike-fashion through space at a speed of about 300,000 km/s.
equatorial anomaly
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.
Fabry-Perot interferometer
An optical instrument used to make extremely fine spectral resolution measurements.
Faraday rotation
Rotation of polarization of a beam of linearly polarized light when it passes through matter in the direction of an applied magnetic field.
GCR
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.
geocorona
The outermost part of Earth’s atmosphere that emits Lyman-alpha radiation under the action of sunlight.
geodesy
The geologic science of the size and shape of Earth.
geomagnetic storm
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).
geospace
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).
GONG
Global Oscillations Network Group
GPS
Global Positioning System
gravity wave
A wave in a fluid medium in which restoring forces are provided primarily by buoyancy (that is, gravity) rather than compression.
H-α line
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.
helioseismology
The analysis of wave motions of the solar surface to determine the structure of the Sun’s interior.
heliosphere
The region surrounding the Sun where the solar wind dominates the interstellar medium.
HF
high frequency
interference fringes
A series of light and dark bands produced by interference of light waves.
ion
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.
ionogram
A graph of the virtual height of the ionosphere plotted against frequency.
ionosonde
A radar system for determining the vertical height at which the ionosphere reflects signals back to Earth at various frequencies.
ionosphere
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.
IPS
Interplanetary scintillation—rapid variation in apparent position, brightness, or color of a distant luminous object viewed through the atmosphere or ionosphere.
ISR
incoherent scatter radar
Kp index
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.
LPM
Low-power magnetometer—a single-battery, non-solar unit designed to last for 1 year (or more) of operation in a polar winter environment.
MACCS
Magnetometer Array for Cusp and Cleft Studies
magnetic flux
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.
magnetic storm
A disturbance or fluctuation in Earth’s magnetic field, associated with solar flares; also called geomagnetic storm.
magnetic substorm
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.
magnetometer
An instrument for measuring the magnitude and sometimes also the direction of a magnetic field, such as Earth’s magnetic field.
magnetopause
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.
magnetosphere
The region around Earth whose processes are dominated by the Earth’s magnetic field, bounded by the magnetopause.
Maunder minimum
The period from roughly 1645 to 1715 A.D. when sunspots became exceedingly rare, as noted by solar observers of the time.
megahertz
Unit of frequency, equal to 1 million cycles per second
meridian
Great circle that passes through both the north and south poles; also called line of longitude.
mesopause
Top of the mesosphere situated at about 80 to 85 km.
mesosphere
A division of Earth’s atmosphere extending from altitudes ranging from 30-50 km to 80-90 km.
MeV
One million electron volts
MHD wave
Wave in a compressible, electrically conducting fluid immersed in a magnetic field.
M-I-T
magnetosphere-ionosphere-thermosphere
NASA
National Aeronautics and Space Administration
neutral line
The line that separates longitudinal magnetic fields of opposite polarity.
NOAA
National Oceanic and Atmospheric Administration
NSF
National Science Foundation
PENGUIn
Polar Experimental Network for Geophysical Upper-atmosphere Investigations
photometry
The measurement of light intensities.
photosphere
The visible surface of the Sun.
planar wave
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.
planetary wave
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.
plasma
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.
plasmapause
Outer periphery of the plasmasphere.
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.
polarization
Orientation of the vibration pattern of light waves in a singular plane.
prominence eruption
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.
quasar
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.
Rayleigh lidar
An optical radar that can probe the upper atmosphere by collecting light from the bulk medium.
ring current
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.
riometer
A specially designed radio receiver for continuous monitoring of the intensity of cosmic noise. (Derived from relative ionospheric opacity meter.)
RISE
Radiative Inputs from the Sun to Earth
SAPS
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.
solar cycle
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.
solar flare
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.
solar limb
The edge of the solar disk.
solar wind
The outward flux of solar particles and magnetic fields from the Sun, typically with velocities close to 350 km/s.
spectrograph
A device that separates light by wavelengths to produce a spectrum.
sunspots
Any of the relatively cool dark spots appearing periodically in groups on the surface of the Sun that are associated with strong magnetic fields.
SuperDARN
A coherent HF radar network of nearly identical, largely automated HF radars that observes scatter of plasma irregularities in the E and F regions.
TEC
total electron content
telemetry
The system for radioing information, including instrument readings and recordings, from a space vehicle to the ground.
THEMIS
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.
thermosphere
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.
TIMED
Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics
tomographic restoration techniques
Mathematical transforms that combine two-dimensional images and create a three-dimensional composite image.
UHF
ultrahigh frequency
ULF
ultralow frequency
undershielded (penetration)
Temporary penetration of dawn-dusk electric field in times of increasing convection.
VHF
very high frequency