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



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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop 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

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop 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).

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop 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.

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop 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.

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop 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.

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop 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

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