Proton gyrofrequency band emissions observed aboard OGO 2

The propagation characteristics of nonpotential ion cyclotron waves traveling at very large angles to the unperturbed magnetic field are discussed. The wave dispersion relationship is derived in situations in which we can use a power series or an asymptotic expansion for the plasma dispersion function, namely, when the phase velocity is less than the electron thermal speed, or when the phase velocity is greater than the electron thermal speed. When the phase velocity is less than the electron thermal speed, it is shown that the analysis includes not only the electrostatic wave investigated by W. E. Drummond and M. N. Rosenbluth, but also a slightly damped nonpotential ion cyclotron mode for any ratio of the plasma pressure to magnetic pressure β. When the phase velocity is greater than the electron thermal speed only the nonpotential ion cyclotron modes exist. These waves have (E • k)/(E ⋏ k)≳1 near the cyclotron harmonics, i.e., at large values of kz (wave number parallel to the magnetic field). At smaller values of kz the ion cyclotron modes tend to be mostly longitudinal. Numerical solutions of the wave dispersion relationship are obtained, and application is made to some relevant space observations. It is shown that the fine structure of the proton whistlers recently observed by D. A. Gurnett and others is well explained by the propagation characteristics of ion (O+) harmonic waves through the ionosphere. Attention is also paid to the recent satellite observations of proton harmonic waves. Finally, the properties of these slow waves near the lower hybrid frequency are discussed.

supporting

confidence: 60%

Nonpotential ion harmonic waves

Stéfant¹

1970

“…A comparison with the observations and conclusions of previous papers on ELF hiss is restricted by the fact that most of them deal with high-latitude and/or high-altitude hiss. Guthart et al [1968] interpreted the ELF hiss observed on Ogo 2 in terms of electrostatic waves. However, for an amplitude of -50 db 7 (on a 40-Hz bandwidth), they need an electrostatic field of 40 v/m.…”

Section: Muzzlo and Angeramimentioning

confidence: 99%

Ogo 4 observations of extremely low frequency hiss

Muzzio¹,

Angerami²

1972

An ELF hiss band with characteristics not previously identified has been observed in data from the Stanford University VLF experiment on Ogo 4. The band exhibits the typical low‐frequency cutoff characteristic of downward‐propagating hiss and also a peculiar upper cutoff in the vicinity of 600 Hz, which is nearly independent of the satellite altitude (∼430 to 900 km) and latitude above ∼15°. This band‐limited ELF hiss (BLH) is observed from ∼10° up to 55° dipole latitude, where the nearly constant upper cutoff and the increasing (with latitude) lower cutoff merge. Around ∼10° dipole latitude, the BLH exhibits a sloping upper cutoff decreasing in frequency toward the equator (equatorial erosion). The BLH is seen most frequently from ∼0600 to ∼2200 LT, although some examples have been found between 0200 and 0500 LT, with less intensity. In the range 0 to 3 kHz and up to ∼55° dipole latitude, the BLH is the strongest signal observed. Its peak amplitude may reach 2 × 10−4 γ²sol;Hz between 40° and 50° dipole latitude during daytime (∼1000 LT). After prolonged periods of low magnetic activity (Kp ≤ 2), the upper cutoff may decrease to as low as 420 Hz but recovers about one day after a sharp increase in magnetic activity, such as a sudden commencement. The decrease and smearing of the lower cutoff of the background hiss, observed at latitudes greater than about 58°, is an indication of the light ion trough. A source location in the equatorial region near L = 4 was found adequate to explain the characteristics of the BLH, as well as some of the observations of ELF hiss previously reported. Two possible generation mechanisms are briefly examined (Cerenkov and Doppler‐shifted cyclotron), but for either a certain amount of emission coherency or amplification is necessary to obtain the observed power fluxes.

“…Similar ELF noise has been reported by Guthart et al [1968] from OGO 2 data and by Burns [1966] and Gurnett and Burns [1968] from Injun 3 data. Guthart et al [1968] have proposed an explanation for such a noise band. They coneluded from observations of the low frequency cutoff near the gyrofrequency that electrostatic proton cyclotron harmonic waves (hereafter, proton CH waves) were involved.…”

Section: Introductionmentioning

confidence: 99%

Evidence of electrostatic proton cyclotron harmonic waves from Alouette 2 satellite data

Harvey¹

1969

An ELF noise band observed by the Alouette 2 receiver has been analyzed using digital power spectrum techniques. Detailed spectra indicate that for altitudes 500–3000 km and all geomagnetic latitudes sharp lower frequency cutoffs of the noise band occur very near to the calculated proton gyrofrequency. Further spectral characteristics are pointed out. All aspects of the noise band are interpreted in terms of ambient electrostatic proton cyclotron harmonic waves. In particular, this hypothesis explains such features of the noise spectra as the upper and lower cutoffs of the noise band at harmonics of the gyrofrequency and the changing character of cutoffs due to changing accessibility conditions and Doppler shifting.