Accession Number : AD0682492

Title :   VLF MODES BELOW AN IDEALIZED ANISOTROPIC IONOSPHERE.

Descriptive Note : Research rept.,

Corporate Author : SYLVANIA ELECTRONIC SYSTEMS-EAST WALTHAM MASS APPLIED RESEARCH LAB

Personal Author(s) : Galejs,J.

Report Date : JAN 1969

Pagination or Media Count : 53

Abstract : The cylindrical shell between the earth and a homogeneous or exponentially varying ionosphere model is excited by vertically or horizontally polarized line sources, and these fields are related to dipole fields in a spherical shell. Because of ionospheric anisotropy, the vertically polarized source excites also TM field components with wave numbers corresponding to TE modes; and a horizontally polarized source excites TE fields corresponding to TM modes, particularly for the higher frequencies at nighttime and for propagation towards west. Among the field components tangential to the ground surface, TM fields tend to dominate with the exception of TE modes at daytime and for lower frequencies also at night. TM modes dominate in the nighttime mode sum (or interference pattern) for propagation towards east, but the two lower TE modes contribute significantly if propagation is towards west. Simplified computational models which neglect the radial component of the earth's static magnetic field are justified under daytime conditions. At nighttime such calculations provide extreme changes in the attenuation rates and phase velocity variations, which are opposite to the ones observed with a dipping static magnetic field. The direction dependence of the phase velocity is eliminated by decreasing the strength of the static magnetic field. (Author)

Descriptors :   (*IONOSPHERIC PROPAGATION, VERY LOW FREQUENCY), ATMOSPHERE MODELS, ANISOTROPY, ATTENUATION, DIURNAL VARIATIONS

Subject Categories : Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE