SUDDEN IONOSPHERIC DISTURBANCES AND THE PROPAGATION OF VERY-LOW- FREQUENCY RADIO WAVES
Abstract
The changes in VLF radio noise accompanying a solar flare and its associated sudden ionospheric disturbance (SID) are surveyed. The onset time of the effects is about 10 minutes, but may be less than 2 minutes for perhaps 5 percent of the incidents. The alteration in propagation conditions implies an increase in noise on frequencies exceeding 20 kc and a decrease below 10 kc. If a local thunderstorm develops, the time phasing is very similar to that of an SID incident, but noise at all frequencies is enhanced. A detailed examination of the formative processes of the lower ionosphere is made. Values of the rate coefficients for attachement, detachment (photo, collisional, and associative), electron-ion recombination, and ion-ion recombination, are deduced for heights from 40 to 100 km. The balance equations for the lower ionosphere are solved for the cases of equilibrium conditions and of the departure from equilibrium associated with the approach of night. Two specific examples indicate that contours of electron density, and therefore of ionospheric conductivity, are far from parallel to the surface of the earth. It follows that the attenuation coefficient for VLF propagation by day can differ according to the solar zenith angle by as much as 20% from the mean daytime value.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1963
- Accession Number
- AD0428169
Entities
People
- Edward T. Pierce
- Helen R. Arnold
Organizations
- SRI International