Cone structure and focusing of VLF and LF electromagnetic waves at high altitudes in the ionosphere
- Harvard Smithsonian Center for Astrophysics, Cambridge, MA (United States)
- NASA/Goddard Space Flight Center, Greenbelt, MD (United States)
The frequency and angle dependencies of the electric field radiated by an electric dipole E = E[sub 0] cos [omega]t are studied through numerical calculations of [vert bar]E[vert bar] in the VLF and LF frequency bands 0.02f[sub b] [le] F [le] 0.5f[sub b] in a model ionosphere over an altitude region of 800-6000 km where the wave frequency and electron gyrofrequency varies between F [approximately]4 - 500 kHz and f[sub b] [approx equal] (1.1 to 0.2) MHz respectively. It is found that the amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth magnetic field line B[sub 0] (it is called the axis field E[sub 0]), in the Storey E[sub St], reversed Storey E[sub RevSt], and resonance E[sub Res] cones. The maximal values of E[sub 0], E[sub Res], and E[sub RevSt] are the most pronounced close to the lower hybrid frequency, F [approximately] F[sub L]. The flux of the electric field is concentrated in very narrow regions, with the apex angles of the cones [delta][beta] [approx equal] (0.1-1) deg. The enhancement and focusing of the electric field increases with altitude starting at Z>800 km. At Z [ge] 1000 up to 6000 km, the relative value of [vert bar]E[vert bar], in comparison with its value at Z = 800 km is about (10[sup 2] to 10[sup 4]) times larger. Thus, the flux of VLF and LF electromagnetic waves generated at high altitudes in the Earth's ionosphere are trapped into very narrow conical beams similar to laser beams. 7 refs., 14 figs., 5 tabs.
- OSTI ID:
- 6720636
- Journal Information:
- Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 99:A1; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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