A

a index -
A-index -
aa index -
active prominence -
active prominence region (APR) -
active region -
active surge region (ASR) -
active dark filament (ADF) -
AE index -
Air Force Geophysics Laboratory (AFGL) -
arch filament system (AFS) -
Air Force Space Forecast Center (AFSFC) -
ak index -
Alfvén wave

Alfvén wave

An Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic wave.-Definition:An Alfvén wave in a plasma is a low-frequency travelling oscillation of the ions and the magnetic field...

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Alaskan Meteorological Data System (ALMEDS) -
am index -
amateur radio bands -
Radio Amateur Satellite Corporation (AMSAT) -
An index -
anomalous propagation

Anomalous propagation

Anomalous propagation includes different forms of electromagnetic wave propagation that are not encountered in a standard atmosphere. While technically the term includes propagation with larger losses than in standard atmosphere, in practical applications it is most often meant to refer to cases...

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antenna height above average terrain

Antenna height above average terrain

In United States telecommunication terminology, antenna height above average terrain is the antenna height above the average terrain elevations from 3.2 to 16 kilometers from the antenna for the eight directions spaced evenly for each 45° of azimuth starting with true north.In general, a different...

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ap index -
aphelion -
apogee -
arcade (solar physics) -
arch filament system -
Area to Area Lee Model

Area to Area Lee Model

Lee Model for Area-to-Area Mode is a Radio propagation model that operates around 900 MHz. Built as two different modes, this model includes an adjustment factor that can be adjusted to make the model more flexible to different regions of propagation....

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American Radio Relay League

American Radio Relay League

The American Radio Relay League is the largest membership association of amateur radio enthusiasts in the USA. ARRL is a non-profit organization, and was founded in May 1914 by Hiram Percy Maxim of Hartford, Connecticut...

 (ARRL) -
As index -
American Standard Code for Information Interchange (ASCII) -
atmospheric duct

Atmospheric duct

In telecommunication, an atmospheric duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if...

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atmospherics

Atmospherics

In marketing the term atmospherics is used to describe the discipline of designing commercial spaces. Atmospherics was coined by Philip Kotler in a 1973 article in the Journal of Retailing.....

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aurora

Aurora (astronomy)

An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...

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auroral electrojet -
auroral oval -
AUTODIN -
autumnal equinox -
Air Weather Service (AWS) -

B

B-angle -
backscatter

Backscatter

In physics, backscatter is the reflection of waves, particles, or signals back to the direction they came from. It is a diffuse reflection due to scattering, as opposed to specular reflection like a mirror...

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Bartels' rotation number

Bartels' Rotation Number

Bartels’ Rotation Number is a serial numbering of the 27-day rotations of the sun, with the first being the rotation of January 1833. It uses a period of exactly 27 days and starts from 8 February 1832....

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bipolar magnetic region -
birefringent filter -
blind zone -
bow shock

Bow shock

A bow shock is the area between a magnetosphere and an ambient medium. For stars, this is typically the boundary between their stellar wind and the interstellar medium....

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bright point -
bright surge on the disk (BSD) -
bright surge on the limb (BSL) -
brightness temperature

Brightness temperature

Brightness temperature is the temperature a black body in thermal equilibrium with its surroundings would have to be to duplicate the observed intensity of a grey body object at a frequency \nu....

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burst (solar physics) -
burst transmission

Burst transmission

In telecommunication, the term burst transmission or data burst has the following meanings:# Any relatively high-bandwidth transmission over a short period of time...

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butterfly diagram

Butterfly diagram

In the context of fast Fourier transform algorithms, a butterfly is a portion of the computation that combines the results of smaller discrete Fourier transforms into a larger DFT, or vice versa . The name "butterfly" comes from the shape of the data-flow diagram in the radix-2 case, as described...

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C

C index -
Carrington longitude -
Cassegrain antenna

Cassegrain antenna

In telecommunications and radar, a Cassegrain antenna is a parabolic antenna in which the feed radiator is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller convex secondary reflector suspended in front of the primary reflector...

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Cassegrain reflector

Cassegrain reflector

The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....

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Castelli U -
celestial equator

Celestial equator

The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space...

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celestial sphere

Celestial sphere

In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

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cellular telephony -
centimeter burst -
central meridian distance (CMP) -
central meridian passage (CMD) -
Chapman function

Chapman function

A Chapman function describes the integration of atmospheric absorption along a slant path on a spherical earth, relative to the vertical case. It applies for any quantity with a concentration decreasing exponentially with increasing altitude...

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chromosphere

Chromosphere

The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....

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chromospheric event -
chromospheric network -
Ci index -
city model -
clutter (radar)

Clutter (radar)

Clutter is a term used for unwanted echoes in electronic systems, particularly in reference to radars. Such echoes are typically returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences, and can cause serious performance issues with radar systems.- Backscatter coefficient...

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clutter folding

Clutter folding

Clutter folding is a term used in describing "clutter" seen by radar systems. Clutter folding becomes a problem when the range extent of the clutter exceeds the pulse repetition frequency interval of the radar, and it no longer provides adequate clutter suppression, and the clutter "folds" back in...

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co-channel interference

Co-channel interference

Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. There can be several causes of co-channel radio interference; four examples are listed here....

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coherence bandwidth

Coherence bandwidth

Coherence bandwidth is a statistical measurement of the range of frequencies over which the channel can be considered "flat", or in other words the approximate maximum bandwidth or frequency interval over which two frequencies of a signal are likely to experience comparable or correlated amplitude...

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coherence time

Coherence time

For an electromagnetic wave, the coherence time is the time over which a propagating wave may be considered coherent...

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COMEDS -
communication with submarines

Communication with submarines

Communication with submarines is difficult because radio waves do not travel well through thick electrical conductors like salt water.The obvious solution is to surface and raise an antenna above the water, then use ordinary radio transmissions. Early submarines had to frequently surface anyway for...

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comprehensive flare index (CFI) -
conjugate points

Conjugate points

In differential geometry, conjugate points are, roughly, points that can almost be joined by a 1-parameter family of geodesics. For example, on a sphere, the north-pole and south-pole are connected by any meridian.-Definition:...

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continuum

Continuum

Continuum may refer to:* Continuum , anything that goes through a gradual transition from one condition, to a different condition, without any abrupt changes-Linguistics:...

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continuum storm (CTM) -
convection

Convection

Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

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Coordinated Universal Time

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

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corona

Corona

A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...

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coronagraph

Coronagraph

A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved...

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coronal hole -
coronal loops -
coronal mass ejection

Coronal mass ejection

A coronal mass ejection is a massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space....

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coronal rain (CRM) -
coronal stream -
coronal streamer -
coronal transients -
corrected geomagnetic coordinates -
cosmic noise

Cosmic noise

Cosmic noise and galactic radio noise is random noise that originates outside the Earth's atmosphere. It can be detected and heard on radio receivers.- Elaboration :Cosmic noise characteristics are similar to those of thermal noise...

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cosmic ray

Cosmic ray

Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...

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COST Hata model -
COST Walfish-Ikegami model -
Cp index

Cp index

In process improvement efforts, the process capability index or process capability ratio is a statistical measure of process capability: The ability of a process to produce output within specification limits. The concept of process capability only holds meaning for processes that are in a state of...

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Crane Global Model -
Crane Model for Satellite Paths -
Crane Two Component Model -
critical frequency

Critical frequency

In telecommunication, the term critical frequency has the following meanings:* In radio propagation by way of the ionosphere, the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an ionospheric layer.* At vertical incidence, the limiting...

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crochet (solar physics) -
CTM

CTM

-Technology:* Chemistry and Transport Models, software to calculate the fate of air pollutants in the atmosphere* Close to Metal, a low-level programming interface* Concepts, Techniques, and Models of Computer Programming, a computer programming textbook...

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cusp (solar physics) -

D

D component of the geomagnetic field -
D region

D region

The D region is the portion of the ionosphere that exists approximately 50 to 95 km above the surface of the Earth.Note: Attenuation of radio waves, caused by ionospheric free-electron density generated by solar radiation, is pronounced during daylight hours. Because solar radiation is not...

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D-Layer -
DAH Model -
Disk And Limb Activity Summary (DALAS) -
dark surge on the disk (DSD) -
decibel

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

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declination

Declination

In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

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delay spread

Delay spread

In telecommunications, the delay spread is a measure of the multipath richness of a communications channel.In general, it can be interpreted as the difference between the time of arrival of the earliest significant multipath component and the time of arrival of the latest multipath component.The...

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differential charging -
differential particle flux -
differential rotation

Differential rotation

Differential rotation is seen when different parts of a rotating object move with different angular velocities at different latitudes and/or depths of the body and/or in time. This indicates that the object is not solid. In fluid objects, such as accretion disks, this leads to shearing...

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dip equator -
dipole antenna

Dipole antenna

A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...

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directional antenna

Directional antenna

A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....

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disappearing solar filament (DSF) -
disparition brusque -
diurnal phase shift

Diurnal phase shift

In telecommunication, diurnal phase shift is the phase shift of electromagnetic signals associated with daily changes in the ionosphere. The major changes usually occur during the period of time when sunrise or sunset is present at critical points along the path. Significant phase shifts may occur...

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diversity scheme

Diversity scheme

In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity plays an important role in combatting fading and co-channel interference and avoiding error bursts...

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data management system (DMS) -
Defense Meteorological Satellite Program

Defense Meteorological Satellite Program

The Defense Meteorological Satellite Program monitors meteorological, oceanographic, and solar-terrestrial physics for the United States Department of Defense. The program is now run by the National Oceanic and Atmospheric Administration. The mission of the satellites was revealed in March 1973...

 (DMSP) -
Department Of Commerce (DOC) -
Department Of Defense (DOD) -
Doppler effect

Doppler effect

The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...

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Doppler shift -
dose rate -
Dst index -
ducting (radio propagation) -
DXing

DXing

DXing is the hobby of tuning in and identifying distant radio or television signals, or making two way radio contact with distant stations in amateur radio, citizens' band radio or other two way radio communications. Many DXers also attempt to receive written verifications of reception from the...

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E

E region -
E-layer -
E-skip -
Early ITU Model

Early ITU Model

The ITU Vegetation Model is a radio propagation model that estimates the path loss encountered due to the presence of one or more trees inside a point to point telecommunication link...

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Earth-Moon-Earth

EME (communications)

Earth-Moon-Earth, also known as moon bounce, is a radio communications technique which relies on the propagation of radio waves from an Earth-based transmitter directed via reflection from the surface of the Moon back to an Earth-based receiver....

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eccentric dipole -
eclipse

Eclipse

An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...

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ecliptic

Ecliptic

The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...

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EFR

EFR

EFR may stand for:* Enhanced Full Rate, a speech coding standard* Economic Faculty Association Rotterdam, a Dutch student organization* École Française de Radioélectricité, now EFREI* Ecological Fiscal Reform, see Ecotax...

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Egli Model

Egli Model

The Egli Model is a terrain model for radio frequency propagation. This model, which was first introduced by John Egli in his 1957 paper, was derived from real-world data on UHF and VHF television transmissions in several large cities. It predicts the total path loss for a point-to-point link...

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EHF

Extremely high frequency

Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low infrared light, also referred to as terahertz radiation...

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electric beacon

Electric beacon

Electric beacons are a kind of beacon used with direction finding equipment to find ones relative bearing to a known location .The term electric beacon includes radio, infrared and sonar beacons.- Radio beacons :...

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electrojet

Electrojet

An electrojet is an electric current which travels around the E region of the Earth's ionosphere. There are two electrojets: above the magnetic equator , and near the Northern and Southern Polar Circles . Electrojets are Hall currents carried primarily by electrons at altitudes from 100 to...

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electromagnetic electron wave

Electromagnetic electron wave

An electromagnetic electron wave is a wave in a plasma which has a magnetic field component and in which primarily the electrons oscillate.In an unmagnetized plasma, an electromagnetic electron wave is simply a light wave modified by the plasma...

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electrostatic discharge

Electrostatic discharge

Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...

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ELF

Extremely low frequency

Extremely low frequency is a term used to describe radiation frequencies from 3 to 300 Hz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz...

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emerging flux region -
emission line -
emission measure -
environmental attenuation model -
Earth Observing System

Earth Observing System

The Earth Observing System is a program of NASA comprising a series of artificial satellite missions and scientific instruments in Earth orbit designed for long-term global observations of the land surface, biosphere, atmosphere, and oceans of the Earth. The satellite component of the program was...

 (EOS) -
ephemeris

Ephemeris

An ephemeris is a table of values that gives the positions of astronomical objects in the sky at a given time or times. Different kinds of ephemerides are used for astronomy and astrology...

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EPL

EPL

- Computing :* Early PL/I, a PL/I subset dialect used to write Multics* Eclipse Public License* Eltron Programming Language, a control language for various computer printers...

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equatorial electrojet

Equatorial electrojet

The equatorial electrojet is a narrow ribbon of current flowing eastward in the day time equatorial region of the Earth's ionosphere. The abnormally large amplitude of variations in the horizontal components measured at equatorial geomagnetic observatories, as a result of EEJ, was noticed as early...

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equinox

Equinox

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...

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Environmental Research Laboratories (ERL) -
eruptive -
eruptive prominence on limb -
Es-layer -
European Space Agency

European Space Agency

The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

 (ESA) -
ESD

ESD

ESD may mean:*Education for Sustainable Development, a vision of education as depicted by the United Nations*Educational service district, a state-level legislative grouping for schools in some US states....

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estimated hemispherical power input -
EUV

Extreme ultraviolet

Extreme Ultraviolet radiation is high-energy ultraviolet radiation, generally defined to be electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 120 nm down to 10 nm, and therefore having photons with energies from 10 eV up to 124 eV...

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Evershed effect

Evershed effect

The Evershed effect, named after the British astronomer John Evershed, is the radial flow of gas across the photospheric surface of the penumbra of sunspots from the inner border with the umbra towards the outer edge....

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exosphere

Exosphere

The exosphere is the uppermost layer of Earth's atmosphere. In the exosphere, an upward travelling molecule moving fast enough to attain escape velocity can escape to space with a low chance of collisions; if it is moving below escape velocity it will be prevented from escaping from the celestial...

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expert system

Expert system

In artificial intelligence, an expert system is a computer system that emulates the decision-making ability of a human expert. Expert systems are designed to solve complex problems by reasoning about knowledge, like an expert, and not by following the procedure of a developer as is the case in...

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extraordinary mode -
extreme ultraviolet

Extreme ultraviolet

Extreme Ultraviolet radiation is high-energy ultraviolet radiation, generally defined to be electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 120 nm down to 10 nm, and therefore having photons with energies from 10 eV up to 124 eV...

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extremely high frequency

Extremely high frequency

Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low infrared light, also referred to as terahertz radiation...

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extremely low frequency

Extremely low frequency

Extremely low frequency is a term used to describe radiation frequencies from 3 to 300 Hz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz...

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F

F corona -
F region

F region

The F region of the ionosphere is home to the F layer of ionization, also called the Appleton layer, after the English physicist Edward Appleton. As with other ionospheric sectors, 'layer' implies a concentration of plasma, while 'region' is the area that contains the said layer...

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F-layer -
f-spot

F-Spot

F-Spot is an image organizer, designed to provide personal photo management for the GNOME desktop environment. The name is a play on the words F-Stop and G-Spot.-Features:...

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F1-layer -
F2-layer -
facula

Facula

A facula , Latin for "little torch", is literally a "bright spot." It is used in planetary nomenclature for naming certain surface features of planets and moons, and is also a type of surface phenomenon on the Sun....

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fade margin

Fade margin

In telecommunication, the term fade margin has the following meanings:*A design allowance that provides for sufficient system gain or sensitivity to accommodate expected fading, for the purpose of ensuring that the required quality of service is maintained.*The amount by which a received signal...

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fading

Fading

In wireless communications, fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media. The fading may vary with time, geographical position and/or radio frequency, and is often modelled as a random process. A fading channel...

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fading distribution

Fading distribution

In telecommunications, a fading distribution is the probability distribution of the value of signal fading relative to a specified reference level....

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fibril (solar physics) -
filament (solar physics) -
filament channel -
flare (solar physics) -
flutter (electronics and communication) -
FM DX -
fmin -
foEs -
foF2 -
follower spot -
Forbush decrease

Forbush decrease

A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection . It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. The term Forbush decrease was named after the American...

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forward scatter

Forward scatter

In telecommunication and astronomy, forward scatter is the deflection—by diffraction, nonhomogeneous refraction, or nonspecular reflection by particulate matter of dimensions that are large with respect to the wavelength in question but small with respect to the beam diameter—of a portion of an...

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Fraunhofer spectrum -
free space -
free-space path loss

Free-space path loss

In telecommunication, free-space path loss is the loss in signal strength of an electromagnetic wave that would result from a line-of-sight path through free space , with no obstacles nearby to cause reflection or diffraction...

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frequency of optimum transmission

Frequency of optimum transmission

Frequency of optimum transmission, in the transmission of radio waves via ionospheric reflection, is the highest effective frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. It is often abbreviated as FOT. The FOT is normally just below the...

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frequency-hopping spread spectrum

Frequency-hopping spread spectrum

Frequency-hopping spread spectrum is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver...

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Fresnel zone

Fresnel zone

In optics and radio communications , a Fresnel zone , named for physicist Augustin-Jean Fresnel, is one of a number of concentric ellipsoids which define volumes in the radiation pattern of a circular aperture...

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Friis transmission equation

Friis transmission equation

The Friis transmission equation is used in telecommunications engineering, and gives the power received by one antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. The formula was derived in 1945 by Danish-American radio engineer Harald T...

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G

gamma (unit of magnetic field intensity) -
gamma rays -
GEOALERT -
geocorona

Geocorona

The geocorona is the luminous part of the outermost region of the Earth's atmosphere, the exosphere. It is seen primarily via far-ultraviolet light from the Sun that is scattered from neutral hydrogen. It extends to at least 15.5 Earth radii...

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geomagnetic activity -
geomagnetic elements -
geomagnetic field -
geomagnetic storm

Geomagnetic storm

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in the interplanetary medium. A geomagnetic storm is a major component of space weather and provides the input for many other components of space weather...

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geomagnetic storm level -
geomagnetic time -
geomagnetism -
geosynchronous -
Geostationary Meteorological Satellite

Geostationary meteorological satellite

Himawari orGeostationary Meteorological Satellite , was a series of Japanese weather satellites operated by the Japan Meteorological Agency. The first GMS satellite was launched 14 July 1977 from Cape Canaveral. The fifth and final satellite was launched 18 March 1995 from Tanegashima...

 (GMS) -
GMT -
Geostationary Operational Environmental Satellite

Geostationary Operational Environmental Satellite

The Geostationary Satellite system, operated by the United States National Environmental Satellite, Data, and Information Service , supports weather forecasting, severe storm tracking, and meteorology research. Spacecraft and ground-based elements of the system work together to provide a continuous...

 (GOES) -
GPS -
gradual commencement -
granule (solar physics)

Granule (solar physics)

Granules on the photosphere of the Sun are caused by convection currents of plasma within the Sun's convective zone. The grainy appearance of the solar photosphere is produced by the tops of these convective cells and is called granulation.The rising part of the granules is located in the center...

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gray-line -
green line

Green Line

- Geographic demarcations :* Green Line, a name for the Gothic Line or "Linea Gotica", a German defensive line in Italy during World War II, renamed the "Green Line" in June 1944...

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Greenwich Mean Time

Greenwich Mean Time

Greenwich Mean Time is a term originally referring to mean solar time at the Royal Observatory in Greenwich, London. It is arguably the same as Coordinated Universal Time and when this is viewed as a time zone the name Greenwich Mean Time is especially used by bodies connected with the United...

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ground wave -
ground level enhancement (GLE) -
ground-level event -
group velocity

Group velocity

The group velocity of a wave is the velocity with which the overall shape of the wave's amplitudes — known as the modulation or envelope of the wave — propagates through space....

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Goddard Space Flight Center

Goddard Space Flight Center

The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...

 (GSFC) -

H

H alpha -
H component -
H-component of the geomagnetic field -
Hale boundary -
High Altitude Observatory

High Altitude Observatory

The High Altitude Observatory conducts research and provides support and facilities for the solar-terrestrial research community in the areas of solar and heliospheric physics, and the effects of solar variability on the Earth's magnetosphere, ionosphere, and upper atmosphere.HAO is a laboratory...

 (HAO) -
Hata Model for Open Areas

Hata Model for Open Areas

The Hata Model for Open Areas, also known as the Okumura-Hata model for being a developed version of the Okumura Model, is the most widely used model in radio frequency propagation for predicting the behavior of cellular transmissions in open areas. This model incorporates the graphical information...

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Hata Model for Suburban Areas

Hata Model for Suburban Areas

The Hata Model for Suburban Areas, also known as the Okumura-Hata model for being a developed version of the Okumura Model, is the most widely used model in radio frequency propagation for predicting the behavior of cellular transmissions in city outskirts and other rural areas...

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Hata Model for Urban Areas

Hata Model for Urban Areas

In wireless communication, the Hata Model for Urban Areas, also known as the Okumura-Hata model for being a developed version of the Okumura Model, is the most widely used radio frequency propagation model for predicting the behaviour of cellular transmissions in built up areas...

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heliographic -
heliopause -
heliosphere

Heliosphere

The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...

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helmet streamer

Helmet streamer

Helmet streamers are bright loop-like structures which develop over active regions on the sun. They are closed magnetic loops which connect regions of opposite magnetic polarity. Electrons are captured in these loops, and cause them to glow very brightly. The solar wind elongates these loops to...

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hemispherical power input -
High Energy Proton and Alpha Detector (HEPAD) -
high frequency

High frequency

High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

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high latitude -
high-speed stream -
High Latitude Monitoring Station (HLMS) -
homologous flare -
HRS type antennas

HRS type antennas

HRS type antennas are more or less the standard antenna used for long distance high power shortwave broadcasting .- History of HRS design :...

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Hubble Space Telescope

Hubble Space Telescope

The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 (HST) -
Hyder flare -

I

International Association of Geomagnetism and Aeronomy

International Association of Geomagnetism and Aeronomy

International Association of Geomagnetism and Aeronomy is the premier international scientific association promoting the study of terrestrial and planetary magnetism and space physics....

 (IAG) -
International Cometary Explorer

International Cometary Explorer

The International Cometary Explorer spacecraft was originally known as International Sun/Earth Explorer 3 satellite, launched August 12, 1978. It was part of the ISEE international cooperative program between NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the...

 (ICE) -
International Geophysical Year

International Geophysical Year

The International Geophysical Year was an international scientific project that lasted from July 1, 1957, to December 31, 1958. It marked the end of a long period during the Cold War when scientific interchange between East and West was seriously interrupted...

 (IGY) -
Interplanetary Monitoring Platform (IMP) -
International Magnetospheric Study

International Magnetospheric Study

The International Magnetospheric Study was proposed in 1970 as a concerted effort to acquire coordinated ground-based, balloon, rocket, and satellite data needed to improve our understanding of the behavior of earth's plasma environment....

 (IMS) -
inclination of the geomagnetic field -
initial phase -
integral particle flux -
International Consortium of Magnetic Observatories (Intermagnet

Intermagnet

Intermagnet is a global network of observatories, monitoring the Earth's magnetic field.- Participating Countries :Intermagnet now has Geomagnetic Information Nodes in 5 continents....

) -
intermediate-field region

Intermediate-field region

Intermediate-field region: For an antenna, the transition region--lying between the near-field region and the far-field region--in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse square of the distance, and the inverse cube of the distance from...

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interplanetary magnetic field

Interplanetary Magnetic Field

The interplanetary magnetic field is the term for the solar magnetic field carried by the solar wind among the planets of the Solar System....

 (IMF) -
invariant magnetic latitude -
inversion (meteorology)

Inversion (meteorology)

In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a temperature inversion, i.e...

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inversion line -
ion-acoustic wave -
ionogram

Ionogram

An ionogram is a display of the data produced by an ionosonde. It is a graph of the virtual height of the ionosphere plotted against frequency. Ionograms are often converted into electron density profiles...

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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...

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ionospheric absorption

Ionospheric absorption

Ionospheric absorption is the scientific name for absorption occurring as a result of the interaction between various types of electromagnetic waves and the free electrons in the ionosphere, which can interfere with radio transmissions.-Description:...

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ionospheric reflection

Ionospheric reflection

Ionospheric reflection is a bending, through a complex process involving reflection and refraction, of electromagnetic waves propagating in the ionosphere back toward the Earth....

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ionospheric sounding

Ionospheric sounding

In telecommunication and radio science, an ionospheric sounding is a technique that provides real-time data on high-frequency ionospheric-dependent radio propagation, using a basic system consisting of a synchronized transmitter and receiver....

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ionospheric storm

Ionospheric storm

An Ionospheric storm is a turbulence in the ionosphere of the Earth's atmosphere. Such storms are triggered by enhanced flux of energetic electrons that are emitted at a large level by the Sun.An Ionospheric storm is also known as an Ion storm...

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international standard relative sunspot number -
International Sun Earth Explorer-3. (ISEE-3) -
International Solar-Terrestrial Program (ISTP) -
ITU Model for Indoor Attenuation

ITU Model for Indoor Attenuation

The ITU Indoor Propagation Model, also known as ITU Model for Indoor Attenuation, is a radio propagation model that estimates the path loss inside a room or a closed area inside a building delimited by walls of any form...

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ITU Rain Attenuation Model -
ITU Rain Attenuation Model for Satellites -
ITU Terrain Model

ITU Terrain Model

The ITU Terrain Loss Model is a radio propagation model that provides a method to predict the median path loss for a telecommunication link. Developed on the basis of diffraction theory, this model predicts the path loss as a function of the height of path blockage and the First Fresnel zone for...

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International Union of Geodesy and Geophysics

International Union of Geodesy and Geophysics

The International Union of Geodesy and Geophysics is a non-governmental organisation dedicated to the scientific study of the Earth using geophysical and geodesic techniques. The IUGG was established in 1919. Some areas within its scope are environmental preservation, reduction of the effects of...

 (IUGG) -
International Ursigram and World Days Service (IUWDS) -

J

Joan-Eleanor system

Joan-Eleanor system

The Joan-Eleanor system was a very high frequency radio system developed during World War II for use by agents working behind enemy lines to relay information and replaced the earlier S-Phone system used by agents....

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Jet Propulsion Laboratory

Jet Propulsion Laboratory

Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...

 (JPL) -
Johnson Space Center (JSC) -

K

K corona -
K index -
K-factor

K-factor

K-factor or K factor may refer to:* K-factor * K-factor * K-factor * K-factor * k-factor * K-factor * K factor crude oil refining* K-factor...

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Kelvin-Helmholtz instability

Kelvin-Helmholtz instability

The Kelvin–Helmholtz instability, after Lord Kelvin and Hermann von Helmholtz, can occur when velocity shear is present within a continuous fluid, or when there is sufficient velocity difference across the interface between two fluids. One example is wind blowing over a water surface, where the...

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Kennelly–Heaviside layer -
Km index -
knife-edge effect

Knife-edge effect

In electromagnetic wave propagation, the knife-edge effect or edge diffraction is a redirection by diffraction of a portion of the incident radiation that strikes a well-defined obstacle such as a mountain range or the edge of a building....

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Kp index -
Kitt Peak National Observatory

Kitt Peak National Observatory

The Kitt Peak National Observatory is a United States astronomical observatory located on 2,096 m Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O'odham Nation, southwest of Tucson...

 (KPNO) -

L

latchup

Latchup

Latchup is a term used in the realm of integrated circuits to describe a particular type of short circuit which can occur in an improperly designed circuit...

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long-delayed echo (LDE) -
leader spot -
LEO

Low Earth orbit

A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

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light bridge -
light curve

Light curve

In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band...

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limb (solar physics) -
limb darkening

Limb darkening

Limb darkening refers to the diminishing of intensity in the image of a star as one moves from the center of the image to the edge or "limb" of the image...

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limb flare -
Line-of-sight propagation

Line-of-sight propagation

Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

 -
linear energy transfer

Linear energy transfer

Linear energy transfer is a measure of the energy transferred to material as an ionizing particle travels through it. Typically, this measure is used to quantify the effects of ionizing radiation on biological specimens or electronic devices....

 (LET) -
List of European medium wave transmitters -
lobe (solar physics) -
Log-distance path loss model -
Long delayed echo

Long delayed echo

Long delayed echoes are radio echoes which return to the sender several seconds after a radio transmission has occurred. Delays of longer than 2.7 seconds are considered LDEs. LDEs are scientific anomalies of uncertain origin.-History:...

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long duration -
longitudinal component -
Longley–Rice model

Longley–Rice model

The Longley–Rice model is a radio propagation model: a method for predicting the attenuation of radio signals for a telecommunication link in the frequency range of 20 MHz to 20 GHz.Longley-Rice is also known as the irregular terrain model...

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loop prominence system (LPS) -
low frequency

Low frequency

Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

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low probability of intercept

Low probability of intercept

A low-probability-of-intercept radar is designed to be difficult to detect by passive radar detection equipment while it is searching for a target or engaged in target tracking...

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low-gain antenna

Low-gain antenna

A low-gain antenna is an antenna with a broad radiowave beam width. This very wide beam allows for a more reliable signal that is best used in mountainous regions, where the signal will propagate reasonably well regardless of terrain. The mountains become the equivalent of rocks in a stream,...

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low-power communication device

Low-power communication device

In telecommunication, a low-power communication device, also short-range device is a restricted radiation device, exclusive of those employing conducted or guided radio frequency techniques, used for the transmission of signs, signals , writing, images and sounds or intelligence of any nature by...

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lowest usable frequency (LUF) -
lowest usable high frequency

Lowest usable high frequency

The lowest usable high frequency , in radio transmission, is that frequency in the HF band at which the received field intensity is sufficient to provide the required signal-to-noise ratio for a specified time period, e.g., 0100 to 0200 UTC, on 90% of the undisturbed days of the month...

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M

M(3000) -
magnetic bay -
magnetic cloud

Magnetic cloud

A magnetic cloud is a transient event observed in the solar wind. It was defined in 1981 by Burlaga et al. 1981 as a region of enhanced magnetic field strength, smooth rotation of the magnetic field vector and low proton density and temperature . Magnetic clouds are a possible manifestation of a...

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magnetic local time -
magnetic sunspot classifications -
magneto-ionic double refraction

Magneto-ionic double refraction

In telecommunication, magneto-ionic double refraction is the combined effect of the Earth's magnetic field and atmospheric ionization, whereby a linearly polarized wave entering the ionosphere is split into two components called the orinary wave and extra-ordinary wave.The component waves follow...

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magnetogram

Magnetogram

The term magnetogram has two meanings, used separately in the contexts of magnetic fields of the Sun and the Earth.In the context of the magnetic field of the Sun, the term magnetogram refers to a pictorial representation of the spatial variations in strength of the solar magnetic field...

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magnetohydrodynamics

Magnetohydrodynamics

Magnetohydrodynamics is an academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water or electrolytes...

 (MHD) -
magnetopause

Magnetopause

The magnetopause is the abrupt boundary between a magnetosphere and the surrounding plasma. For planetary science, the magnetopause is the boundary between the planet’s magnetic field and the solar wind. The location of the magnetopause is determined by the balance between the pressure of the...

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magnetopause current sheet -
magnetosheath

Magnetosheath

The magnetosheath is the region of space between the magnetopause and the bow shock of a planet's magnetosphere. The regularly organized magnetic field generated by the planet becomes weak and irregular in the magnetosheath due to interaction with the incoming solar wind, and is incapable of fully...

 -
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,...

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magnetotail -
MAGSTORM -
main phase -
material scattering

Material scattering

Material scattering of an electromagnetic wave is scattering that is attributable to the intrinsic properties of the material through which the wave is propagating. Ionospheric scattering and Rayleigh scattering are examples of material scattering...

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Maunder minimum

Maunder Minimum

The Maunder Minimum is the name used for the period roughly spanning 1645 to 1715 when sunspots became exceedingly rare, as noted by solar observers of the time....

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maximum usable frequency

Maximum usable frequency

Maximum usable frequency describes, in radio transmission, using reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time, independent of transmitter power...

 (MUF) -
medium frequency

Medium frequency

Medium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...

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Medium Energy Proton and Electron Detector (MEPED) -
mesosphere

Mesosphere

The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...

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meteor burst communications

Meteor burst communications

Meteor burst communications , also referred to as meteor scatter communications, is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communications paths between radio stations up to apart.-How it works:As the earth moves along its...

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meteor scatter -
micropulsation -
microwave burst -
microwaves -
middle latitude -
Mie theory

Mie theory

The Mie solution to Maxwell's equations describes the scattering of electromagnetic radiation by a sphere...

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miniprop

Miniprop

A DOS application written by Sheldon Shallon , Miniprop is used to predict the probability of a high frequency radio signal path between two points on the Earth's surface...

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Moreton wave

Moreton wave

A Moreton wave is the chromospheric signature of a large-scale solar coronal shock wave. Described as a kind of solar 'tsunami', they are generated by solar flares. They are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank who spotted them in 1959...

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mound prominence (MDP) -
Marshall Space Flight Center

Marshall Space Flight Center

The George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program...

 (MSFC) -
Multipath interference

Multipath interference

Multipath interference is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and, under the right condition, the two components of the wave interfere...

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Multipath propagation -
mush zone

Mush zone

In mediumwave broadcasting, a mush zone is a region where the ground wave and sky wave from a transmitter are received at approximately equal signal strength, resulting in interference between the two, which will typically cause fading and distorted audio....

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MW DX

MW DX

MW DX, short for mediumwave DXing, is the hobby of receiving the reception of distant mediumwave radio stations. MW DX is similar to TV and FM DX in that broadcast band stations are the reception targets...

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N

Naval Astronautics Group (NAG) -
National Aeronautics and Space Administration (NASA) -
National Bureau of Standards (NBS) -
National Center for Atmospheric Research

National Center for Atmospheric Research

The National Center for Atmospheric Research has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. NCAR is managed by the nonprofit University Corporation for Atmospheric Research and sponsored by the National Science Foundation...

 (NCAR) -
Near Vertical Incidence Skywave

Near Vertical Incidence Skywave

Near Vertical Incidence Skywave, or NVIS, is a radio-wave propagation method that provides usable signals in the range between groundwave and skywave distances . It is used mainly for military and paramilitary communications and by radio amateurs...

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National Environmental Satellite, Data, and Information Service (NESDIS) -
National Environmental Satellite Service (NESS) -
neutron monitor

Neutron monitor

A neutron monitor is a ground-based detector designed to measure the number of high-energy charged particles striking the Earth's atmosphere from outer space. For historical reasons the incoming particles are called "cosmic rays", but in fact they are particles, predominantly protons and Helium...

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New Horizons

New Horizons

New Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...

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National Geophysical Data Center

National Geophysical Data Center

The National Geophysical Data Center provides scientific stewardship, products and services for geophysical data describing the solid earth, marine, and solar-terrestrial environment, as well as earth observations from space....

 (NGDC) -
National Geophysical and Solar-Terrestrial Data Center (NGSDC) -
National Institute of Standards and Technology

National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...

 (NIST) -
National Oceanic and Atmospheric Administration

National Oceanic and Atmospheric Administration

The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 (NOAA) -
National Optical Astronomy Observatories (NOAO) -
noise storm -
non-great-circle propagation -
non-line-of-sight propagation

Non-line-of-sight propagation

Non-line-of-sight or near-line-of-sight is a term used to describe radio transmission across a path that is partially obstructed, usually by a physical object in the innermost Fresnel zone....

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Northern Meteorological Data System (NORMEDS) -
Naval Ocean Systems Center (NOSC) -
Naval Research Laboratory (NRL) -
National Science Foundation

National Science Foundation

The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 (NSF) -
National Solar Observatory

National Solar Observatory

The mission of the National Solar Observatory is to advance knowledge of the Sun, both as an astronomical object and as the dominant external influence on Earth, by providing forefront observational opportunities to the research community...

 (NSO) -
National Space Science Data Center

National Space Science Data Center

The National Space Science Data Center serves as the permanent archive for NASA space science mission data. "Space science" pertains to astronomy and astrophysics, solar and space plasma physics, and planetary and lunar science...

 (NSSDC) -

O

Okumura Model

Okumura Model

The Okumura model for Urban Areas is a Radio propagation model that was built using the data collected in the city of Tokyo, Japan. The model is ideal for using in cities with many urban structures but not many tall blocking structures. The model served as a base for the Hata Model.Okumura model...

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On-Line Data Systems (OLDS) -
One Woodland Terminal Model

One Woodland Terminal Model

The ITU Terrestrial Model for One Terminal in Woodland is a Radio propagation model belonging to the class of Foliage models. This model is a successor of the Early ITU Model.-Applicable To / Under Conditions:...

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ordinary mode -

P

P-angle -
p-spot -
p.f.u. -
particle flux unit -
path loss

Path loss

Path loss is the reduction in power density of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system....

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path profile

Path profile

In telecommunication, a path profile is a graphic representation of the physical features of a propagation path in the vertical plane containing both endpoints of the path, showing the surface of the Earth and including trees, buildings, and other features that may obstruct the radio...

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path quality analysis

Path quality analysis

Path quality analysis: In a communications path, an analysis that includes the overall evaluation of the component quality measures, the individual link quality measures, and the aggregate path quality measures, and is performed by evaluating communications parameters, such as bit error ratio,...

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penumbra -
perigee

Perigee

Perigee is the point at which an object makes its closest approach to the Earth.. Often the term is used in a broader sense to define the point in an orbit where the orbiting body is closest to the body it orbits. The opposite is the apogee, the farthest or highest point.The Greek prefix "peri"...

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perihelion -
persistence

Persistence

Persistence may refer to:* Image persistence, in LCD monitors* Multidrug tolerance, a dormant, persistent state of a bacterial population* Persistence , the characteristic of data that outlives the execution of the program that created it...

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phantom command -
photosphere

Photosphere

The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

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photospheric network -
Pioneer 10

Pioneer 10

Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...

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Pioneer 11

Pioneer 11

Pioneer 11 is a 259-kilogram robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere...

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Pioneer program

Pioneer program

The Pioneer program is a series of United States unmanned space missions that was designed for planetary exploration. There were a number of such missions in the program, but the most notable were Pioneer 10 and Pioneer 11, which explored the outer planets and left the solar system...

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pitch angle

Pitch angle

The pitch angle of a charged particle is the angle between the particle's velocity vector and the local magnetic field. This is a common measurement and topic when studying the magnetosphere. See Aurora and Ring current-Usage: Particle motion:...

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plage (solar physics) -
plage corridor -
plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

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plasma frequency -
plasmapause -
plasmasheet -
plasmasphere

Plasmasphere

The plasmasphere, or inner magnetosphere, is a region of the Earth's magnetosphere consisting of low energy plasma. It is located above the ionosphere...

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Point to Point Lee Model -
Point-to-Point propagation model -
polar cap absorption (PCA) -
polar crown -
polar plume -
polar rain -
pore (solar physics) -
post-flare loops -
power delay profile

Power delay profile

The power delay profile gives the intensity of a signal received through a multipath channel as a function of time delay. The time delay is the difference in travel time between multipath arrivals...

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preheating -
PRESTO

Presto

-As a common word:* An incantation or interjection used by some stage magicians* A musical score marking indicating a fast tempo* An exclamation to mean: [to be completed] right away, instantly, i.e. "magically"-Places:*Presto, Bolivia...

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prominence -
Propagation path obstruction

Propagation path obstruction

In telecommunication, a propagation path obstruction is a man-made or natural physical feature that lies near enough to a radio path to cause a measurable effect on path loss, exclusive of reflection effects. An obstruction may lie to the side, above, or below the path. Ridges, bridges, cliffs,...

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proton event -
pulsation -

R

radiation belt -
radiation scattering -
radio blackout -
radio burst -
radio emission -
radio frequency

Radio frequency

Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

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radio horizon -
radio propagation beacon

Radio propagation beacon

A radio propagation beacon is a radio beacon, whose purpose is the investigation of the propagation of radio signals. Most radio propagation beacons use amateur radio frequencies. They can be found on HF, VHF, UHF, and microwave frequencies...

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radio propagation model

Radio propagation model

A radio propagation model, also known as the Radio Wave Propagation Model or the Radio Frequency Propagation Model, is an empirical mathematical formulation for the characterization of radio wave propagation as a function of frequency, distance and other conditions...

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RAIM

RAIM

Receiver Autonomous Integrity Monitoring is a technology developed to assess the integrity of Global Positioning System signals in a GPS receiver system. It is of special importance in safety-critical GPS applications, such as in aviation or marine navigation.-General description:RAIM detects...

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ray tracing (physics)

Ray tracing (physics)

In physics, ray tracing is a method for calculating the path of waves or particles through a system with regions of varying propagation velocity, absorption characteristics, and reflecting surfaces. Under these circumstances, wavefronts may bend, change direction, or reflect off surfaces,...

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Rayleigh fading

Rayleigh fading

Rayleigh fading is a statistical model for the effect of a propagation environment on a radio signal, such as that used by wireless devices.Rayleigh fading models assume that the magnitude of a signal that has passed through such a transmission medium will vary randomly, or fade, according to a...

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Rayleigh–Taylor instability -
reconnection -
recurrence

Recurrence

Recurrence and recurrent may refer to:*Recurrence relation, an equation which defines a sequence recursively*Poincaré recurrence theorem, Henri Poincaré's theorem on dynamical systems...

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red line

Red Line

Red Line may refer to:* Red line , denotes the center of the playing surface on an ice hockey rink* Red Line Synthetic Oil Corporation, an oil manufacturer for automotive and other performance applications...

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region number -
relative transmission level

Relative transmission level

In telecommunication, relative transmission level is the ratio of the signal power, at a given point in a transmission system, to a reference signal power....

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Remote Geophysical Observing Network (RGON) -
Rician fading

Rician fading

Ricean fading is a stochastic model for radio propagation anomaly caused by partial cancellation of a radio signal by itself — the signal arrives at the receiver by several different paths , and at least one of the paths is changing...

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right ascension

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

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rigidity (solar physics) -
ring current

Ring current

A ring current is an electric current carried by charged particles trapped in a planet's magnetosphere. It is caused by the longitudinal drift of energetic particles.-Earth's ring current:...

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riometer

Riometer

A riometer is an instrument used to quantify the amount of electromagnetic wave ionospheric absorption in the atmosphere. As the name implies, a riometer measures the ``opacity" of the ionosphere to radio noise emanating from distant stars and galaxies...

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Radio Solar Telescope Network

Radio Solar Telescope Network

The Radio Solar Telescope Network is a network of solar observatories maintained and operated by the U.S.Air Force Weather Agency. The RSTN consists of ground-based observatories in Australia, Italy, Massachusetts, New Mexico and Hawaii.- History :...

 (RSTN) -
rudimentary (solar physics) -
Regional Warning Center (RWC) -

S

S component -
s.f.u. -
satellite anomaly -
Schumann resonance

Schumann resonance

The Schumann resonances are a set of spectrum peaks in the extremely low frequency portion of the Earth's electromagnetic field spectrum...

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Science Institute (ScI) -
scintillation

Scintillation

Scintillation can refer to:*Scintillation , atmospheric effects which influence astronomical observations*Interplanetary scintillation, fluctuations of radio waves caused by the solar wind...

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sector boundary -
Space Environment Laboratory (SEL) -
selective fading

Selective fading

Selective fading or frequency selective fading is a radio propagation anomaly caused by partial cancellation of a radio signal by itself — the signal arrives at the receiver by two different paths, and at least one of the paths is changing...

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Space Environment Laboratory Solar Imaging System (SELSIS) -
Space Environment Monitor (SEM) -
Solar Electro-Optical Network (SEON) -
Space Environment Services Center (SESC) -
Space Forecast Center (SFC) -
Solar Geophysical Activity Summary (SGAS) -
Shadow loss

Shadow loss

In telecommunication, the term shadow loss has the following meanings:# The attenuation caused to a radio signal by obstructions in the propagation path....

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shock

Shock

Circulatory shock, commonly known simply as shock, is a life-threatening medical condition that occurs due to inadequate substrate for aerobic cellular respiration...

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short wave fade -
shortwave relay station

Shortwave relay station

Shortwave relay stations are transmitter sites used by international broadcasters to extend their coverage to areas that cannot be reached easily from their home state, for example the BBC operates an extensive net of relay stations....

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Solar Influences Data Analysis Center (SIDC) -
side lobe

Side lobe

In antenna engineering, side lobes or sidelobes are the lobes of the far field radiation pattern that are not the main lobe....

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sidereal

Sidereal

Sidereal, of the stars, may refer to:* Measurements of time:** Sidereal time** Sidereal day** Sidereal month** Sidereal year* Sidereal period of an object orbiting a star* Sidereal astrology...

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Signal-to-Interference Ratio

Signal-to-interference ratio

The signal-to-interference ratio , also known as the carrier-to-interference ratio , is the quotient between the average received modulated carrier power S or C and the average received co-channel interference power I, i.e...

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simultaneous flares -
single event upset

Single event upset

A single event upset is a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device, such as in a microprocessor, semiconductor memory, or power transistors. The state change is a result of the free charge created by ionization in or close...

 (SEU) -
Single Vegetative Obstruction Model

Single Vegetative Obstruction Model

The ITU Single Vegetative Obstruction Model is a Radio propagation model that quantitatively approximates the attenuation due to the vegetation in the middle of a telecommunication link.-Applicable to/under conditions:...

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skip (radio) -
skip zone

Skip zone

A skip zone, also called a silent zone or zone of silence, is a region where a radio transmission can not be received located between regions both nearer and further from the transmitter where reception is possible....

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sky wave -
skywave

Skywave

Skywave is the propagation of electromagnetic waves bent back to the Earth's surface by the ionosphere. As a result of skywave propagation, a broadcast signal from a distant AM broadcasting station at night, or from a shortwave radio station can sometimes be heard as clearly as local...

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Solar Maximum Mission

Solar Maximum Mission

The Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....

 (SMM) -
smoothed sunspot number -
Synchronous Meteorological Satellite

Synchronous Meteorological Satellite

For the Synchronous Meteorological Satellite program, NASA developed two weather satellites which were placed into geosynchronous orbit. SMS-1 was launched May 17, 1974 a and SMS-2 was launched February 6, 1975. Both satellites were carried to orbit by Delta 2914 rockets...

 (SMS) -
Software-defined radio

Software-defined radio

A software-defined radio system, or SDR, is a radio communication system where components that have been typically implemented in hardware are instead implemented by means of software on a personal computer or embedded computing devices...

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solar activity -
solar constant

Solar constant

The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit...

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solar coordinates -
solar cycle

Solar cycle

The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...

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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...

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solar flare effect (SFE) -
solar flux -
solar flux unit -
solar maximum

Solar maximum

Solar maximum or solar max is the period of greatest solar activity in the solar cycle of the sun. During solar maximum, sunspots appear....

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solar minimum

Solar minimum

Solar minimum is the period of least solar activity in the solar cycle of the sun. During this time, sunspot and solar flare activity diminishes, and often does not occur for days at a time...

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solar radiation storm level -
solar radio emission -
solar rotation rate -
solar sector boundary -
solar wind

Solar wind

The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

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solstice

Solstice

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

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Solar Observing Optical Network

Solar Observing Optical Network

The Solar Observing Optical Network consists of three U.S. Air Force Air Weather Service observatories. The Air Force operates a solar telescope at each site to monitor solar active regions at optical wavelengths...

 (SOON) -
South Atlantic 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...

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Southern Hemisphere Auroral Radar Experiment

Southern Hemisphere Auroral Radar Experiment

The Southern Hemisphere Auroral Radar Experiment , started 1988, is an Antarctic research project designed to observe velocities and irregularities of electrical fields in the ionosphere and magnetosphere...

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Space weather

Space weather

Space weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...

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spacecraft charging -
Space Physics Analysis Network (SPAN) -
spicule (solar physics)

Spicule (solar physics)

In solar physics, a spicule is a dynamic jet of about 500 km diameter in the chromosphere of the Sun. It moves upwards at about 20 km/s from the photosphere...

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sporadic E -
Sporadic E propagation

Sporadic E propagation

Sporadic E or Es is an unusual form of radio propagation using characteristics of the Earth's ionosphere. Whereas most forms of skywave propagation use the normal and cyclic ionization properties of the ionosphere's F region to refract radio signals back toward the Earth's surface, sporadic E...

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spray (solar physics) -
spread F -
Spread spectrum

Spread spectrum

Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...

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stratosphere

Stratosphere

The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

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STRATWARM -
subflare -
substorm

Substorm

A substorm, sometimes referred to as a magnetospheric substorm or an auroral substorm, is a brief disturbance in the Earth's magnetosphere that causes energy to be released from the "tail" of the magnetosphere and injected into the high latitude ionosphere. Visually, a substorm is seen as a sudden...

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sudden commencement -
sudden impulse -
sudden ionospheric disturbance

Sudden Ionospheric Disturbance

A sudden ionospheric disturbance is an abnormally high ionization/plasma density in the D region of the ionosphere caused by a solar flare...

 (SID) -
sunspot

Sunspot

Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

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sunspot classification -
sunspot cycle -
sunspot number -
super high frequency

Super high frequency

Super high frequency refers to radio frequencies in the range of 3 GHz and 30 GHz. This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from ten to one centimetres....

 (SHF) -
supergranulation

Supergranulation

Supergranulation is a particular pattern on the Sun's surface. It was discovered in the 1950s by A.B.Hart using Doppler velocity measurements showing horizontal flows on the photosphere ....

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Surface wave

Surface wave

In physics, a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient...

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surge

Surge

Surge was a citrus soft drink first introduced in Norway, under the name Urge , by the Coca-Cola Company to compete with Pepsi's Mountain Dew.-History:...

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SWF

SWF

SWF is an Adobe Flash file format used for multimedia, vector graphics and ActionScript. Originating with FutureWave Software, then transferred to Macromedia, and then coming under the control of Adobe, SWF files can contain animations or applets of varying degrees of interactivity and function.,...

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Solar X-ray Imager

Solar X-ray Imager

-Operation:The Solar X-ray Imager aboard the GOES 12, GOES 13, GOES 14, and GOES 15 United States NOAA weather satellites is used for early detection of solar flares, coronal mass ejections, and space phenomena that impact human spaceflight and military and commercial satellite communications...

 (SXI) -
sympathetic flare -
synodic -
synoptic chart -

T

T-index -
Tracking and Data Relay Satellite

Tracking and Data Relay Satellite

A Tracking and Data Relay Satellite is a type of communications satellite that forms part of the Tracking and Data Relay Satellite System used by NASA and other United States government agencies for communications to and from independent "User Platforms" such as satellites, balloons, aircraft,...

 (TDRS) -
trans-equatorial propagation (TEP) -
total electron content

Total electron content

Total electron content is an important descriptive quantity for the ionosphere of the Earth. TEC is the total number of electrons present along a path between two points, with units of electrons per square meter, where 1016 electrons/m² = 1 TEC unit .TEC is significant in determining the...

 (TEC) -
Total Energy Detector (TED) -
telemetry

Telemetry

Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...

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tenflare -
terrain model -
thermal fade

Thermal fade

A thermal fade is a phenomenon of wireless signal degradation caused by temperature and relative humidity factors. As the prevailing environmental conditions change, for example, from hot to cool, humid to arid or day to night, the electromagnetic waves refract differently thus altering the power...

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thermosphere

Thermosphere

The thermosphere is the biggest of all the layers of the Earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization. The International Space Station has a stable orbit within the middle of the thermosphere, between...

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Time signal

Time signal

A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:...

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Television and Infrared Radiation Observation Satellite (TIROS) -
Table Mountain Observatory

Table Mountain Observatory

Table Mountain Observatory is an astronomical observation facility operated by NASA's Jet Propulsion Laboratory...

 (TMO) -
total electron content

Total electron content

Total electron content is an important descriptive quantity for the ionosphere of the Earth. TEC is the total number of electrons present along a path between two points, with units of electrons per square meter, where 1016 electrons/m² = 1 TEC unit .TEC is significant in determining the...

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transition region -
troposphere

Troposphere

The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

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tropospheric scatter

Tropospheric scatter

Tropospheric scatter is a method of transmitting and receiving microwave radio signals over considerable distances – often up to 300 km...

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tropospheric wave

Tropospheric wave

In telecommunication, a tropospheric wave is a radio wave that is propagated by reflection from a place of abrupt change in the dielectric constant, or its gradient, in the troposphere. In some cases, a ground wave may be so altered that new components appear to arise from reflection in regions of...

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TV and FM DX -
TV-FM DX

TV-FM DX

TV DX and FM DX is the active search for distant radio or television stations received during unusual atmospheric conditions. The term DX is an old telegraphic term meaning "long distance."...

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two-ribbon flare -

U

U-burst -
UHF -
UHF CB

UHF CB

UHF CB is a class-licensed citizen's band radio service authorised by the governments of Australia and New Zealand in the UHF 477 MHz band. UHF CB provides 77 channels, including 32 channels allocated to repeater stations...

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ultrahigh frequency -
ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

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umbra

Umbra

The umbra, penumbra and antumbra are the names given to three distinct parts of a shadow, created by any light source. For a point source only the umbra is cast.These names are most often used to refer to the shadows cast by celestial bodies....

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UMR

UMR

UMR may stand for:* Underground Media Revolution, a music e-zine in Pakistan* Uninitialized Memory Reads* University of Missouri–Rolla, former name of the Missouri University of Science and Technology* University of Minnesota Rochester* Unreal Media Ripper...

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unipolar magnetic region -
Universal Time

Universal Time

Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...

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unsettled (solar physics) -
upsets (solar physics) -
Union Radio Scientifique Internationale (URSI) -
United States Air Force

United States Air Force

The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

 (USAF) -
United States Geological Survey

United States Geological Survey

The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

 (USGS) -
United States Space Forecast Center (USSFC) -
Universal Time

Universal Time

Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...

 (UT) -
UTC -

V

Van Allen radiation belts -
vernal equinox -
very high frequency

Very high frequency

Very high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...

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very low frequency

Very low frequency

225px|thumb|right|A VLF receiving antenna at [[Palmer Station]], Antarctica, operated by Stanford UniversityVery low frequency or VLF refers to radio frequencies in the range of 3 kHz to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals...

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VHF -
VLF -
VMB4

VMB4

VMB4 is a UHF Citizens' Band Radio Repeater located one kilometre from Mount Sugarloaf on the Sugarloaf Range in Newcastle, New South Wales, Australia. VMB4 is Newcastle's fourth repeater to go to air in the Hunter Valley....

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Voyager 1

Voyager 1

The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...

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Voyager 2

Voyager 2

The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

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Voyager program

Voyager program

The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...

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W

wave propagation

Wave propagation

Wave propagation is any of the ways in which waves travel.With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves....

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World Data Center

World Data Center

The World Data Center system was created to archive and distribute data collected from the observational programs of the 1957-1958 International Geophysical Year. Originally established in the United States, Europe, Soviet Union, and Japan, the WDC system has since expanded to other countries and...

 (WDC) -
Weibull fading

Weibull fading

Weibull fading, named after Waloddi Weibull, is a simple statistical model of fading used in wireless communications and based on the Weibull distribution...

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Weissberger's model

Weissberger's Model

Weissberger’s modified exponential decay model, or simply, Weissberger’s model, is a radio wave propagation model that estimates the path loss due to the presence of one or more trees in a point-to-point telecommunication link...

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White Alice Communications System

White Alice Communications System

The White Alice Communications System was a United States Air Force telecommunication link system constructed in Alaska during the cold war. It featured tropospheric scatter links and line-of-sight microwave radio links...

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white light

White Light

White Light may refer to:*Light with the color white*White Light , a 1980 novel by Rudy Rucke*White Light , 1971 album*White Light , 2010 album...

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white-light flare -
wing (spectroscopy) -
World Meteorological Organization

World Meteorological Organization

The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 (WMO) -
Wolf number

Wolf number

The Wolf number is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the sun....

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World Warning Agency (WWA) -
WWV

WWV

WWV is the call sign of the United States National Institute of Standards and Technology's HF radio station in Fort Collins, Colorado. WWV continuously transmits official U.S. Government frequency and time signals on 2.5, 5, 10, 15 and 20 MHz...

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X

X band

X band

The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...

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X-band -
X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

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X-ray background

X-ray background

The observed X-ray background is thought to result from, at the "soft" end , Galactic X-ray emission , and, at the "hard" end , from a combination of many unresolved X-ray sources outside of the Milky Way .The galactic X-ray background is produced largely by emission from hot gas in the Local...

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X-ray burst -
X-ray flare class -
X-ray flare termination -

Z

Z component of the geomagnetic field -
Zeeman effect

Zeeman effect

The Zeeman effect is the splitting of a spectral line into several components in the presence of a static magnetic field. It is analogous to the Stark effect, the splitting of a spectral line into several components in the presence of an electric field...

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Zurich sunspot classification -
Zurich sunspot number -