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OGO 5 observations of quasi-trapped electromagnetic waves in the solar wind

1970; American Geophysical Union; Volume: 75; Issue: 19 Linguagem: Inglês

10.1029/ja075i019p03735

2156-2202

F. L. Scarf, R. W. Fredricks, I. M. Green, M. Neugebauer,

Geomagnetism and Paleomagnetism Studies

On April 5, 1968, a flare-associated sudden commencement was detected as OGO 5 was outbound through the bow shock region. Several hours later exceptionally high densities (Ne>70/cm³) were encountered, and, when the flux decreased by a moderate factor, large-amplitude 70-kHz noise bursts were sporadically detected on the VLF electric and magnetic sensors. We interpret the oscillations with correlated E and B components as electromagnetic waves that have n²≃1 - ωp²/ω² <1, and direct comparison with the plasma probe density estimate gives an absolute calibration for that instrument. The measured wave amplitudes are also used to evaluate the local density from the relation n = cB/E, thus leading to an absolute calibration for the electric dipole within the streaming plasma. We find that all measured or deduced densities are in agreement and are compatible with the interpretation that the correlated noise bursts represent electromagnetic waves with ω near the local plasma resonance frequency. These observations are related to previous measurements of 20- to 30-kHz electric fields in the solar wind (Zond 3, Venus 2, Pioneer 8 and 9, and Luna 11 and 12), and the problem of distinguishing between electromagnetic waves of this type and electrostatic plasma oscillations is considered.