Sporadic E propagation is a relatively rare form of propagation where a radio wave bounces off a sporadic E cloud, notated as E_s in the E layer region of the ionosphere. Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ...

The E region of the ionosphere is located about 90 to 160 km in altitude. The height can vary a little, and, along with electron (ionization) density, depends on solar zenith angle and solar activity. During daylight hours, electron density (a measure of the ionization level) can reach 10⁵ electrons/cm³. At night, when the supply of x-rays from the sun is cut off, ionization levels drop to 10³ e/cm³. These ionization densities are expected under normal conditions, absent of sporadic E. Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ... 20 years of solar irradiance data from satellites Solar variation refers to fluctuation in the amount of energy emitted by the Sun. ...

A precise definition of E_s can be found in the book titled "Worldwide Occurrence of Sporadic E", written by Ernest K. Smith, Ph.D., 1957. He defines Sporadic E as "a comparatively strong and protracted transmission (several minutes to several hours) "returned" from the E region of the ionosphere by some mechanism other than the normal reflection process from the daytime E layer." Doctor of Philosophy (Ph. ...

Single "clouds" or multiple layers of "clouds" have been observed to form, usually spaced by about 6 km. The mechanisms for how these clouds form is still not precisely known. Some possible theorized mechanisms include upper level wind shears and geomagnetic activity. The cause of Earths magnetic field (the surface magnetic field) is not known for certain, but is possibly explained by dynamo theory. ...

Communication distances of 500–1400 miles are common from a single Es cloud. The distance variability of Es propagation is due to cloud height and density. Depending on the density of the ionization, frequencies from 27–110 MHz are most common (USA TV channels 2-6, all USA FM channels (88–106 MHz), amateur radio bands 10, and 6 meters). With strong events, frequencies up through 250 MHz have been reflected off the clounds (USA TV Channel 7, amateur bands 144 MHz and 220 MHz). MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... Braun HF 1, Germany, 1958. ... Mrs. ...

Unsolved problems in physics: How do E layer "clouds" form?