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The ionosphere is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth.
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynamo.
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The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the thermosphere thus constitutes the larger part of the ionosphere. Taking its name from the Greek θερμός meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to 2,000 °C (3,630 °F) or more. Radiation causes the atmospheric particles in this layer to become electrically charged, enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375 mi) above sea level, the atmosphere turns into space, although, by the judging criteria set for the definition of the Kármán line, the thermosphere itself is part of space. The border between the thermosphere and exosphere is known as the thermopause.
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The impact of the solar wind onto the magnetosphere generates an electric field within the inner magnetosphere - the convection field-. Its general direction is from dawn to dusk. The co-rotating thermal plasma within the inner magnetosphere drifts orthogonal to that field and to the geomagnetic field Bo. The generation process is not yet completely understood. One possibility is viscous interaction between solar wind and the boundary layer of the magnetosphere (magnetopause). Another process may be magnetic reconnection. Finally, a hydromagnetic dynamo process in the polar regions of the inner magnetosphere may be possible. Direct measurements via satellites have given a fairly good picture of the structure of that field. A number of models of that field exists.
In the height region between about 85 and 200 km altitude on Earth, the ionospheric plasma is electrically conducting. Atmospheric tidal winds due to differential solar heating or due to gravitational lunar forcing move the ionospheric plasma against the geomagnetic field lines thus generating electric fields and currents just like a dynamo coil moving against magnetic field lines. That region is therefore called ionospheric dynamo region. The magnetic manifestation of these electric currents on the ground can be observed during magnetospheric quiet conditions. They are called Sq-variations and L-variations (L=lunar) of the geomagnetic field. Additional electric currents are generated by the varying magnetospheric electric convection field. These are the DP1-currents and the polar DP2-currents. Finally, a polar-ring current has been derived from the observations which depends on the polarity of the interplanetary magnetic field. These geomagnetic variations belong to the so-called external part of the geomagnetic field. Their amplitudes reach at most about 1% of the main internal geomagnetic field Bo.
Solar phenomena are the natural phenomena occurring within the outer atmosphere of the Sun. These phenomena take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots.
References
- ↑ Ratcliffe, J A (1972). An Introduction to Ionosphere and Magnetosphere . CUP Archive. p. 86. ISBN 978-0-521-08341-6.
- ↑ White, Marvin L. (1957), "On the atmospheric dynamo theory", Journal of Geophysical Research, 62 (2): 329–330, Bibcode:1957JGR....62..329W, doi:10.1029/JZ062i002p00329
- ↑ NASA – Sounding Rockets Study How Winds In Space Drive Currents in the Upper Atmosphere
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