Low region of the ionosphere (~50-90km in altitude) where most HF absorption occurs. Present during daylight hours. This region does not refract HF radio waves but does attenuate them. Top

The region of the ionosphere (~50-90km in altitude) where most HF absorption occurs. Present during daylight hours only. This region does not refract HF radio waves but does attenuate them. Top

A leader that propagates continuously in a channel previously ionized by return stroke of a lightning flash. Top

Dart leader that propagates partially through a channel previously used by a preceding return stroke and partially through virgin air during its way to the ground. Top

When flares occur, increased absorption of a radio wave in the D region may make part of the HF spectrum unusable. At times, the whole HF spectrum is affected, but normally the lower frequencies are affected most. Only those circuits with daylight sectors may be affected. Top

A tenth portion or band of a set of data. A decile is a proportion of a set of data that has been ranked and divided into ten groups (or bands), where each group contains an equal number of data items. Top

In terrestrial magnetism, at any given location, the angle between the geographical meridian and the magnetic meridian; that is, the angle between true north and magnetic north is the declination. Declination is measured either east or west as the compass needle points to the east or west of the geographical meridian. East is taken as the positive direction. Top

It is a property of each kind of material defined as the rate of mass per unit volume. In the International System of Units (SI) the unit for the mass density is kilograms per cubic meter. Top

Electric current per area unit. Top

When referring to the Electron Density is the function of the density with height. Top

Absorption of a radio wave near the point of refraction. Top

Thermodynamic process where there is exchange heat among the parts of the system. Top

It is an enhancement to Global Positioning System that uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. Top

Refers to the fact that the rotation of the Sun varies with latitude. Rotation of plasma near the equator of the Sun is generally faster. This occurs because the Sun is not a solid body. Top

It is digital device used to determine ionospheric characteristics above the vicinity of the instrument. Top

Describe the geometric strength of satellite configuration on GPS accuracy. Top

It is the angle that the geomagnetic field is tilted with respect to the surface of the Earth. Top

It is a pair of equal and opposite electric charges or magnetic poles separated by a small distance. The electric or magnetic field lines leave a pole and enter in other with opposite polarity. Top

When referring to the Sun, it is the visible hemisphere. Top

Electric fields generated at high latitudes, due to the dynamic interaction between the solar wind and the magnetosphere, which penetrate directly to lower latitudes through the conductivity ionosphere. Top

Through the day. Top

Gravity waves guide in the atmosphere formed by vertical wind gradient in the same wave propagation direction, inside of which a gravity wave can propagate through long distances. Top

Change in the wave frequency due to relative motion between source and observer. Top

The region lying further away from the Sun than the Earth, where the solar wind is downstream from the Earth. Top

(in plasma physics) It is the motion of the guiding center of a particle. Top

The Dst is a geomagnetic index which measure the temporal development and intensity of magnetic storms and the ring current. Top

Dual frequency GPS receivers will provide a faster, more accurate, and more reliable solution than single frequency equipment. Top