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The Effects of Ions on Very‐Low‐Frequency Propagation During Polar‐Cap Absorption Events
Author(s) -
Field E. C.
Publication year - 1970
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/rs005i003p00591
Subject(s) - daytime , ionosphere , attenuation , computational physics , very low frequency , physics , absorption (acoustics) , range (aeronautics) , atmospheric sciences , geophysics , polar , optics , materials science , astronomy , composite material
The propagation of electromagnetic waves in the VLF range in the earth‐ionosphere waveguide has been theoretically analyzed. The results of full‐wave calculations indicate that transpolar VLF waves suffer considerably more attenuation during a moderately strong polarcap absorption (PCA) event than during the undisturbed daytime. Computed height profiles of dissipation and field strengths show clearly that this increased attenuation is due mainly to ohmic losses associated with ion heating. Calculations based on a model of a relatively weak PCA event indicate no pronounced increase in attenuation at most VLF frequencies. For this model, ions are found not to be an important factor. The calculations do not include the possible effects of the Greenland ice cap. During a moderately strong PCA event, the height range over which long‐path VLF waves interact strongly with the ionosphere is substantially lower than in the undisturbed daytime. For all ionospheric models considered, the width of the height range of substantial wave‐ionosphere interaction at a given frequency was less than about 20 km. VLF probing experiments must therefore use several frequencies and incidence angles if a broader ionospheric height range is to be sampled effectively.