sphero-, spher-, -sphere-
(Greek: ball, round, around; globe, global; body of globular form; by extension, circular zone, circular area)
2. A disturbance that affects ionospheric scatter communications resulting from the penetration of meteors through the D region of the ionospheric layer.
2. A temporal variation in electron concentration in the ionosphere which is caused by solar activity and that makes the heights of the ionosphere layers go beyond the normal limits for a location, date, and time of day.
2. All systematic and random errors caused by the reception of a navigation signal after ionospheric reflection.
2. Propagation of radio waves over long distances by reflection from the ionosphere, useful at frequencies up to about 25 megahertz.
2. A radio device for determining the distribution of virtual height with frequency, and the critical frequencies of the various "layers" of the ionosphere.
A pulse at a certain frequency is transmitted vertically, and the time for its return is recorded on an oscilloscope; another pulse at a different frequency is then transmitted and timed.
The process is repeated until the entire frequency range of interest, usually from about 1 to 25 MHz, has been explored.3. A radio device for determining the distribution of virtual height with frequency, and the critical frequencies of the various layers of the ionosphere.
2. A form of scatter propagation in which radio waves are scattered by the lower E layer of the ionosphere to permit communication over distances from 600 to 1400 miles (1000 to 2250 kilometers) when using the frequency range of about 25 to 100 megahertz.
2. Term used to denote the major changes that take place in the F-region as a result of solar activity.
Ionospheric storms are closely associated with magnetic storms and can lead to severe disruptions of radio-wave propagation, particularly at high latitudes.3. A turbulence in the F region of the ionosphere, usually due to a sudden burst of radiation from the sun.
It is accompanied by a decrease in the density of ionization and an increase in the virtual height of the region.
In general, there are two phases of an ionospheric storm, an initial increase in electron density (the positive phase) lasting a few hours, followed by a decrease lasting a few days.
At low latitudes only the positive phase is usually seen. Individual storms can vary, and their behavior depends on geomagnetic latitude, season, and local time.
2. A radio wave that travels upward into space and may or may not be returned to earth by reflection from the ionosphere.
3. A radio wave that is transmitted around the curved surface of the earth by being reflected back to earth by the ionosphere.
It is made up of six major and several minor tectonic plates that move around on the softer asthenosphere or the relatively plastic layer of the upper mantle of the earth on which the tectonic plates of the lithosphere move.
It is about 55 km (34 mi) thick beneath the oceans and up to about 200 km (124 mi) thick beneath the continents and is composed of rigid plates.
The high velocity with which seismic waves propagate through the lithosphere suggests that it is completely solid.
The movement of the plates of the lithosphere results in convergence, or collisions, that can form mountain belts and subduction zones, and divergence of the plates and the creation of new crust as material wells up from below separating plates. The lithosphere and asthenosphere are distinguished from the crust, mantle and core of the earth on the basis of their mechanical behavior and not their composition.
2. A region between five hundred and several thousand miles above the earth's surface, in which charged particles are trapped by the earth's magnetic field.
2. The solid part of the earth's mantle lying between the asthenosphere and the core.
3. The atmospheric shell between about 28-35 and 50-60 miles (45-55 and 80-95 kilometers), extending from the top of the stratosphere to the mesopause; characterized by a temperature that generally decreases with altitude.
2. Any of various minute globules; such as, the hollow particles used in making lighter plastics or a cell-like structure resembling a proteinoid or a protein-like polypeptide formed abiotically from amino acid mixtures in the presence of heat and which may resemble early evolutionary forms of protein.