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Spacecraft observations of man‐made whistler‐mode signals near the electron gyrofrequency
Author(s) -
Dunckel N.,
Helliwell R. A.
Publication year - 1977
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs012i005p00821
Subject(s) - plasmasphere , physics , whistler , magnetosphere , ionosphere , electron , electron precipitation , van allen radiation belt , earth's magnetic field , equator , geomagnetic latitude , computational physics , plasma oscillation , rocket (weapon) , substorm , plasma , geophysics , magnetic field , latitude , astronomy , quantum mechanics , aerospace engineering , engineering
Whistler‐mode signals from low‐frequency ground‐based transmitters in the 60–100 kHz range are observed by the OGO‐1 satellite at frequencies unusually close to the local electron gyrofrequency, ƒ H . The intensity of signals observed on outbound passes near 40° geomagnetic latitude remains high until the decrease in ƒ H causes the normalized frequency ƒ/ƒ H to approach 0.9. Here the signal disappears abruptly into the background noise, a change of at least 20 dB. Ray‐tracing calculations provide a simple explanation for the sudden loss of signal. Rays in this frequency range which are launched just inside the plasmapause reach an altitude where ƒ/ƒ H ≃ 0.9 before abruptly bending inward toward the earth's equator. Rays launched outside the plasmapause are reflected in the form of a “Spitze” at the point where the plasma frequency decreases to the wave frequency. Thus the primary features of the observed LF propagation in the magnetosphere can be explained using classical cold‐plasma expressions for the refractive index.