An indicator of the effect of solar activity on HF frequencies. The T index is an indicator of the highest frequencies able to be refracted from regions in the ionosphere. The higher the T index, the higher the frequencies able to be refracted from an ionospheric region.

It is caused by tangential stress between the solar wind and the Earth's field, that drags the Earth's field lines and plasma antisunward, forming a long magnetic tail behind the Earth. The tail current flows across the midnight meridian in the same direction as the ring current. Its main effect at the surface of the Earth is to reduce the total field.

The two bundles of nearly-parallel magnetic field lines which stretch into the magnetotail, on opposite sides of the plasma sheet. The northern lobe contains field lines entering the north polar region of Earth, while the southern lobe contains lines emerging from the southern polar region.

When referring to RO (SEE Radio Occultation) is the point of path of occultation which is crossed by the line perpendicular to the Earth’s surface. The Tangent Point changes with time because of the satellites positions.

Measured of the mean kinetic energy of the random particle motions.

SEE Inversion Layer.

The power output of the Sun at a wavelength of 10.7 centimeters, frequently used in place of sunspot number as an indicator of solar activity.

It is a fictive line that delimits the illuminated day side and the dark night side of a planetary body. The orientation of the terminator between the northern and southern hemispheres depends on the season.

Planets that have intern composition similar to Earth. The four planets closer from Sun (Mercurial, Venus, Earth and Mars).

Tesla is a unit for the magnetic inductance B (which is also known as "magnetic flux density" or just magnetic field) and on SI denotes 1Volt times second per square meter.

Heliographic Telescope for the Study of Magnetism and Solar Instabilities.

Gravity waves guide in the atmosphere formed by vertical temperature gradient, inside of which a gravity wave can propagate through long distances.

It is located at the top of the thermosphere. The solar constant is expressed in this layer.

It is a layer of Earth which begins about 90 km above the surface and it’s the biggest layer of the atmosphere, directly above the mesosphere and directly below the exosphere. In this layer temperature increases monotonously with altitude due to absorption of highly energetic solar radiation by the small amount of residual oxygen still present.

The number of electrons along a wave path measured in electrons per square centimeter. The TEC is used in determining delay and directional changes of a wave in the ionosphere.

It is a short-lived electrical phenomenon to refer to the various types of electrical-discharge phenomena in the upper atmosphere. TLE’ s include red sprites, sprite halos, blue jets, gigantic jets, and elves.

It is part of the Earth’s mantle, and is located between the lower mantle and the upper mantle, between a depth of 410 and 660 kilometers.

These are wave-like motions in the ionosphere that cause focusing and defocusing of radio waves. The disturbance usually appears at higher frequencies, gradually affecting lower frequencies. Some are associated with magnetic storms and originate in the auroral zone. These may travel great distances. Others appear to be more localized, originating in the troposphere in local weather.

The tropopause is the atmospheric boundary between the troposphere and the stratosphere.

The lowest layer of the Earth's atmosphere extending up to about 13 km in altitude.

It is a fluid regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.