1. A reference to or characteristic of the dawn or the period of dusk before sunrise: "When we woke up in the morning, we could see a dim auroral glow in the sky."
2. Pertaining to or referring to the Aurora Borealis or the Aurora Australis.

A large increase of electric and radio wave density in the D-level of the atmosphere caused by electron-bombardment of the atmosphere during an aurora or a geomagnetic storm.

1. The polar regions within the auroral zones.
2. The areas surrounding the auroral poles which are lying between the poles and the auroral zones.

A strong current of electricity which flows through the auroral zone during a polar substorm.

A geomagnetic perturbation (confusion or disorder) lasting one to two hours, which tends to occur during a local post-midnight time.

The magnitude of the substorm is largest in the auroral zone and corresponds to an injection of charged particles from the magnetotail into the auroral oval.

Any of the various shapes of auroral emissions:

• Arcs, bands of arching light extending across the sky.
• Rays, beams of light, appearing singularly or in bundles.
• Draperies, sheets of light spreading across the sky.
• Crowns, rays which seem to emanate from a common point.
• Diffuse aurora, scattered cloud-like surfaces.

The percentage of nights on which an aurora is seen at a given location or place on earth, or on which one would be seen if clouds don't interfere.

An imaginary line which connects areas of equal auroral intensity or frequency that can be observed and averaged over a number of years.

A prominent green or red line which can be seen in the spectra of auroras which corresponds to certain forbidden transitions of the neutral oxygen atom.

An oval-shaped or a rounded-like-an-egg region, centered on the Northern magnetic pole or the Southern magnetic pole, within which auroral emissions take place.

The sites or points on the earth's surface at which the auroral isochasms are centered or coincide with the magnetic-axis poles of the geomagnetic field.

Isochasms are lines on a map or chart connecting points where auroras are observed with equal frequency.

A magnetic pole is either one of the two variable points on the earth's surface towards which a compass needle points.

The propagation or chain reaction of radio waves which are reflected from the aurora in the presence of unusual solar activity.

The geographic area in either hemisphere from which auroral activity can normally be seen; usually, within 30 degrees magnetic latitude from each magnetic pole.

A series of auroral substorms coming in rapid succession during a geomagnetic storm.

A characteristic pattern or sequence of an auroral episode, consisting of the intensification and movements of auroral emissions which occur about midnight in which auroral arcs move rapidly toward the pole, producing a bulge in the auroral oval.

The region of maximum auroral activity around either geomagnetic pole within which there is a maximum of auroral activity that lies 10 to 15 degrees geomagnetic latitude from the geomagnetic poles.

1. A term used with reference to the disruption of communications within the auroral zone as a result of the increased ionization in the atmosphere.
2. The communication fadeout in the auroral zone usually as a result of an increase of ionization in the lower atmosphere.