Of the white-light corona, that portion which is caused by sunlight scattered or reflected by solid particles (dust) in interplanetary space. The same phenomenon produces zodiacal light. Top

A region in the ionosphere located above about 140 km and capable of refracting HF radio waves. During the day, the region often divides into a lower F1 region and an upper F2 region. At night there is only an F region. The F region may be used for HF sky wave communications at any time. Top

Electric current system produced primarily by thermospheric winds on the charged particles in the ionosphere F region. Top

It is an optical instrument that use the interpherometric principle to obtain thermospheric winds from airglow emissions. It is typically made of a transparent plate with two reflecting surfaces, or two parallel highly reflecting mirrors. Top

A bright region of the photosphere seen in white light, seldom visible except near the solar limb. Top

It is a temperature scale, degree Fahrenheit. where the melting point of water is 32 degrees and the boiling point of 212 degrees. Top

The fast solar wind has a typical velocity of 750 km/s, a temperature of 8E5 Kelvin and it nearly matches the composition of the Sun's photosphere. It is thought to originate from coronal holes, which are funnel-like regions of open field lines in the Sun's magnetic field. Such open lines are particularly prevalent around the Sun's magnetic poles. Top

A linear pattern in the H-alpha cromosphere of the Sun, as seen through an H-alpha filter, occurring near strong sunspots and plage or in filament channels. Top

A Birkeland current is a specific magnetic field aligned current in the Earth’s magnetosphere which flows from the magnetotail towards the Earth on the dawn side and in the other direction on the dusk side of the magnetosphere. Top

A cool, relatively dense region in the corona that appears dark against the background chromosphere. On the Sun's limb, filaments are called prominences. Top

In aeronomy, filter wheel is a wheel with airglow emission filters used in imagers to measure the airglow. Top

An explosion on the Sun usually releasing large amounts of energy and particles, and usually occurring within an active region. Flares are more likely at solar maximum. Top

The rate of flow of a physical quantity through a reference surface. Top

The lowest frequency displayed on an ionogram. It can be an indication of the amount of absorption occurring in the ionosphere. Top

The critical frequency of the E region. The maximum frequency which can be refracted vertically from this region. Top

The maximum ordinary mode radiowave frequency capable of reflection from the sporadic E region of the ionosphere (SEE Sporadic Layer). Top

The critical frequency of the F2 region. It is the maximum ordinary mode radiowave frequency which can be refracted vertically by the F2 region. Frequencies higher than this normally penetrate the ionosphere. Top

Spectral emission lines violating quantum mechanics selection rules for electric dipole emission. In both permitted and forbidden transitions, the photon of a spectral line is emitted when an electron moves from an upper to a lower energy level. The photon energy is equal to the difference between the energy of the two levels. Top

A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following an interplanetary coronal mass ejection (ICME). It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. Top

Ionospheric fountain effect is a response of the equatorial plasma due to the zonal electric field (eastward during the day), at the magnetic equator, which undergo vertical electromagnetic drift. The enhancement of the effect causes a greater separation between the crests of EIA. Top

Electron which is not bonded to an atom or molecule. Top

Number of repetitions of an event per unit time. Top

Refers to radio frequencies (RF) in the range of 87.5 to 108 megahertz. Top