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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]
The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's magnetic dipole field — about 10 −4 teslas at the surface of the Sun [ citation needed ] — would reduce with the ...
However, it is now known that electromagnetic waves do not require a physical transmission medium, and so can travel through the vacuum of free space. Regions of the insulative vacuum can become conductive for electrical conduction through the presence of free electrons, holes, or ions.
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. [1]: 26‑1 As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. [2]
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]
Artistic rendition of the Earth's magnetopause. The magnetopause is where the pressure from the solar wind and the planet's magnetic field are equal. The position of the Sun would be far to the left in this image. The magnetopause is the abrupt boundary between a magnetosphere and the surrounding plasma.
The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's 10 −4 tesla magnetic dipole field would reduce with the cube of the distance to about 10 −11 tesla.
In the early work on the chemical composition of the sun the only elements that were detected in spectra were hydrogen and various metals, [11]: 23–24 with the term metallic frequently used when describing them. [11]: Part 2 In contemporary usage in astronomy all the extra elements beyond just hydrogen and helium are termed metallic.