Accession Number : AD0666532

Title :   SOLAR FLARE EFFECTS AND VLF RADIO WAVE OBSERVATIONS OF THE LOWER IONOSPHERE.

Descriptive Note : Technical rept.,

Corporate Author : ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (ENGLAND)

Personal Author(s) : Burgess,B. ; Jones,T. B.

Report Date : AUG 1967

Pagination or Media Count : 23

Abstract : The observed changes of phase and signal amplitude of VLF radio waves, propagated over distances varying between 1000 and 10000 km, which accompany solar flares have been studied for the period 1961-1964. In general the phase of the received signal advances and the signal amplitude increases during the onset of a solar flare. However observations of the GBR transmissions at Rome (1500 km path) show that for this particular path the phase of the received signal retards in contrast to all other paths studied. Assuming that the conductivity of the lower ionosphere varies exponentially with height under both quiet and disturbed conditions, it is possible to evaluate the waveguide mode characteristics of VLF propagation over large distances. Using this theoretical approach it has been shown that the observations can only be interpreted if both the D region electron density profile is lowered and the gradient of ionisation density increased. The magnitude of the flare produced changes in ionisation density profiles of the lower ionosphere have been evaluated analytically from solar X-ray data. These profile changes are consistent with the lowering of the D region and increase in ionisation gradient that is required to explain the VLF radio wave observations. (Author)

Descriptors :   (*SOLAR FLARES, *IONOSPHERIC PROPAGATION), IONOSPHERIC DISTURBANCES, PHASE SHIFT CIRCUITS, IONIZATION, ELECTRON DENSITY, X RAYS, SOLAR DISTURBANCES, RADIO WAVES, COSMIC RAYS, VERY LOW FREQUENCY

Subject Categories : Atmospheric Physics
      Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE