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Schematic of the Birkeland or Field-Aligned Currents and the ionospheric current systems they connect to, Pedersen and Hall currents. [1]A Birkeland current (also known as field-aligned current, FAC) is a set of electrical currents that flow along geomagnetic field lines connecting the Earth's magnetosphere to the Earth's high latitude ionosphere.
A current sheet is an electric current that is confined to a surface, rather than being spread through a volume of space. Current sheets feature in magnetohydrodynamics (MHD), a model of electrically conductive fluids : if there is an electric current through part of the volume of such a fluid, magnetic forces tend to expel it from the fluid ...
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.
A transport equation, usually of heat (sometimes of light element concentration): = + where T is temperature, = / is the thermal diffusivity with k thermal conductivity, heat capacity, and density, and is an optional heat source. Often the pressure is the dynamic pressure, with the hydrostatic pressure and centripetal potential removed.
Since d 2 = 0, the 3-form J satisfies the conservation of current (continuity equation): = = The current 3-form can be integrated over a 3-dimensional space-time region. The physical interpretation of this integral is the charge in that region if it is spacelike, or the amount of charge that flows through a surface in a certain amount of time ...
The radial current in the circuit is on the order of 3 × 10 9 amperes. [2] As a comparison with other astrophysical electric currents, the Birkeland currents that supply the Earth's aurora are about a thousand times weaker at a million amperes. The maximum current density in the sheet is on the order of 10 −10 A/m 2 (10 −4 A/km 2).
This template should be used to present information on both intrinsic and induced planetary magnetospheres belonging to both Solar System and extrasolar planets. For the parameters see example template on the right.
A rendering of the magnetic field lines of the magnetosphere of the 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. [1] [2] It is created by a celestial body with an active interior dynamo.