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Atmospheric ions created by cosmic rays and natural radioactivity move in the electric field, so a very small current flows through the atmosphere, even away from thunderstorms. Near the surface of the Earth, the magnitude of the field is on average around 100 V/m, [4] oriented such that it drives positive charges down. [5]
Ground conductivity is an extremely important factor in determining the field strength and propagation of surface wave (ground wave) radio transmissions. Low frequency (30–300 kHz) and medium frequency (300–3000 kHz) radio transmissions are particularly reliant on good ground conductivity as their primary propagation is by surface wave. [1]
A global atmospheric electrical circuit is the continuous movement of atmospheric charge carriers, such as ions, between an upper conductive layer (often an ionosphere) and surface. The global circuit concept is closely related to atmospheric electricity , but not all atmospheres necessarily have a global electric circuit. [ 2 ]
Overall, this results in a bulk movement in the direction of the electric field such that a current is able to flow, which is known as the Pedersen Current, with the associated Pedersen Conductivity reaching a maximum when the frequency of collisions is approximately equal to the gyratory frequency so that the charge carriers experience one ...
The worldwide solar-driven wind results in the so-called Sq (solar quiet) current system in the E region of the Earth's ionosphere (ionospheric dynamo region) (100–130 km (60–80 mi) altitude). [citation needed] Resulting from this current is an electrostatic field directed west–east (dawn–dusk) in the equatorial day side of the ionosphere.
The magnetic field of a magnetic dipole has an inverse cubic dependence in distance, so its order of magnitude at the earth surface can be approximated by multiplying the above result with (R outer core ⁄ R Earth) 3 = (2890 ⁄ 6370) 3 = 0.093 , giving 2.5×10 −5 Tesla, not far from the measured value of 3×10 −5 Tesla at the equator.
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.
For antennas near a half-wavelength high (180 electrical degrees [b]) the antenna has a voltage maximum near its base, which results in strong electric fields in the earth above the ground wires near the mast where the displacement current enters the ground. To reduce this loss these antennas often use a conductive copper ground screen under ...