Publication Date:
1997-01-01
Description:
A new approach toward an understanding of the nature of ULF-ultra low frequency-em. waves observed in the magnetosphere is given in this paper. The work is based upon results derived from detailed studies of the Fourier spectra of experimental magnetic field data obtained at a number of different geomagnetic locations around the world: Cascade (L = 2.9; Iowa, U.S.A.), Iqaluit - NP (L= 13; Northwest Territories, Canada), Amundsen-Scott Station - SP (L = 13; Antarctica), and also at Tuckerton (L = 2.6; New Jersey), and Point Arena (L = 2.6; California). The frequency band of the examined oscillations is F ≅ (0.7·10-3-5·10-2) Hz and overlaps the frequencies of the so-called (Pc2-Pc5) micropulsations. We show that the em. oscillations of these packets of waves exist in any time both in quite and disturbed conditions in the em. background of the magnetosphere. They appear to be resonance oscillations occurring in the magnetosphere on the whole or on its parts. During the intervals studied, in the examined frequency range 12 fundamental resonance frequencies were found in the spectra of the NP and SP data and more than 20-25 resonance frequencies in the Tuckerton and Point Arena data.* The other resonance maxima disappear in the weak oscillations of the noise. In general, the em. background of the magnetosphere is of a “lined” structure. It is composed of the resonance oscillations (frequency maxima of its spectra), and by more weak oscillations-by noise. All these oscillations can be set swinging, producing isolated, short-lived packets of waves. The conditions for producing the swinging can be impulse/shock-excitations of the magnetospheric plasmas, swinging of the background oscillations by gyro-resonance instability, dynamic effects such as changes in the neutral winds, etc. Thus, the wellknown multiple manifestations of hydromagnetic ULF waves and wave packets observed in the magnetosphere are considered to be the result of a single physical phenomenon: the fundamental em. oscillatory nature of the background magnetospheric plasma environment.
Print ISSN:
0022-1392
Topics:
Geosciences
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