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The radio window is the region of the radio spectrum that penetrate the Earth's atmosphere. Typically, the lower limit of the radio window's range has a value of about 10 MHz (λ ≈ 30 m); the best upper limit achievable from optimal terrestrial observation sites is equal to approximately 1 THz (λ ≈ 0.3 mm).
An atmospheric window is a region of the electromagnetic spectrum that can pass through the atmosphere of Earth. The optical , infrared and radio windows comprise the three main atmospheric windows. [ 2 ]
Relationship of the atmosphere and ionosphere. The ionosphere (/ aɪ ˈ ɒ n ə ˌ s f ɪər /) [1] [2] is the ionized part of the upper atmosphere of Earth, from about 48 km (30 mi) to 965 km (600 mi) above sea level, [3] a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar ...
A fragmented part of the 'window' spectrum (one might say a louvred part of the 'window') can also be seen in the visible to mid-wavelength infrared between 0.2 and 5.5 μm. The infrared atmospheric window is an atmospheric window in the infrared spectrum where there is relatively little absorption of terrestrial thermal radiation by ...
The ions make the air weakly conductive; different locations, and meteorological conditions have different electrical conductivity. Fair weather describes the atmosphere away from thunderstorms where this weak electrical current between the ionosphere and the ground flows. [7]
St. Elmo's Fire and normal sparks both can appear when high electrical voltage affects a gas. St. Elmo's fire is seen during thunderstorms when the ground below the storm is electrically charged, and there is high voltage in the air between the cloud and the ground. The voltage tears apart the air molecules and the gas begins to glow.
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.
Scientific experiments have been conducted to induce airglow by directing high-power radio emissions at the Earth's ionosphere. [8] These radiowaves interact with the ionosphere to induce faint but visible optical light at specific wavelengths under certain conditions. [9] The effect is also observable in the radio frequency band, using ionosondes.