Meteor Ionization

ionization in the upper atmosphere caused by the intrusion of meteoric matter. Active meteor ionization takes place chiefly in collisions of evaporated and detached meteor atoms with air molecules. The average number of free electrons produced by one meteor atom is approximately proportional to the fourth power of its velocity and, in the range of meteor velocities from 11 to 73 km/sec, varies from 0.001 to 1. Active meteor ionization is most intensive at altitudes of 80–120 km, where most meteoroids are vaporized. Above 120 km, active meteor ionization is caused by detached meteor atoms and atmospheric molecules that rebound on impact with the meteoroid. Another source of ions of meteoric origin is the ionization of meteor atoms that are constantly present in the upper atmosphere by the action of solar radiation and as a result of ion charge exchange.

Such meteor ions as Mg⁺, Si⁺, Ca⁺, and Fe+ have been found at altitudes of 80–180 km by means of mass-spectrometric measurements conducted from rockets of the ion composition of the upper atmosphere. The highest concentration of meteor ions (10²–10⁴ per cm³) is observed at altitudes of 80–120 km, where it may be comparable to the concentration of the principal atmospheric ions NO⁴ and O₂⁺. The recombination of atomic meteor ions takes place much more slowly than the recombination of molecular atmospheric ions, and therefore meteor ionization plays a significant role in maintaining nighttime ionization in the E region of the ionosphere; it is also important in the formation of sporadic E_s layers (in E_s layers with a high electron concentration meteor ions may be dominant). Meteor ionization is due primarily to sporadic meteoroids and increases only insignificantly during the time of action of annual meteor streams. However, it increases sharply during meteor showers; for example, the formation of an E_s layer was observed during the Draconids meteor shower of Oct. 10, 1946.

A trail of ionization up to several tens of kilometers in length with an initial diameter of up to a few meters remains in the wake of a meteor. The ionized meteor trail expands rapidly by diffusion. The electron concentration in the trail also decreases as a result of the recombination of electrons and the capture of electrons by neutral atoms in the atmosphere. Ionized meteor trails reflect radio waves in the ultrashort and shortwave regions; this fact is used in meteoric-scatter radio communication systems and for radar studies of meteors and the upper atmosphere.