The zone of the earth's upper atmosphere, between 80- and 500-km altitude, where charged subatomic particles (chiefly protons and electrons) are trapped by the earth's magnetic field. ~ See Also: Van Allen belts.
an ionized (converted into ions)region of the atmosphere above the stratosphere, extending to about 1000 km above the earth's surface and able to reflect radio waves for long-distance transmission round the earth.
The upper layer of the atmosphere above the stratosphere, from a distance of about 80 kilometers from the earth's surface. Incoming solar radiation is sufficiently intense to cause the ionization of the sparse gas molecules present. By absorbing the more intense frequencies in the solar radiation (x-rays and above), the ionosphere protects living beings from their harmful effects.