VLF electric field observations in the magnetosphere

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188

An intense band of electromagnetic noise is frequently observed near the magnetic equatorial plane at radial distance from about 2 to 5 RE. Recent wide band wave form measurements with the Imp 6 and Hawkeye 1 satellites have shown that the equatorial noise consists of a complex superposition of many harmonically spaced lines. Several distinctly different frequency spacings are often evident in the same spectrum. The frequency spacing typically ranges from a few hertz to a few tens of hertz. The purpose of this paper is to suggest that these waves are interacting with energetic protons, alpha particles, and other heavy ions trapped near the magnetic equator. The possible role that these waves play in controlling the distribution of the energetic ions is considered.

Section: Discussionmentioning

confidence: 99%

Plasma wave interactions with energetic ions near the magnetic equator

Gurnett¹

1976

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188

“…The strong pitch angle diffusion is believed to be caused by electrostatic electron cyclotron waves [Kennel et al, 1970 andLyons, 1974]. The theory has been reviewed by Kennel and Ashour-Abdalla [1982].…”

Section: Introductionmentioning

confidence: 99%

Particle and wave dynamics during plasma injections

Koons¹,

Fennell²

1983

The SCATHA satellite measures particle and wave parameters as it moves outbound on the duskside from the plasmasphere into the plasma sheet. In many cases, plasma waves are not observed in the quiescent plasma sheet prior to a plasma injection. The electron distribution function prior to entry into the plasma sheet is a nearly isotropic soft spectrum, J(E) ∼ 1/E. Just inside the plasma sheet the spectrum begins to harden and becomes anisotropic, J⊥ > J∥. As the satellite penetrates deeper into the plasma sheet, the spectrum further hardens, especially near α0 ∼ 90°. At the injection the electron spectrum drastically hardens and often becomes peaked in the keV energy range. The pitch angle anisotropy is further enhanced in favor of J⊥. The plasma wave emissions onset occurred at the time of the injection. Whistler mode waves are observed below the electron cyclotron frequency. Electrostatic waves are detected in bands between the electron cyclotron frequency harmonics.

“…The first approach, by Fredricks [1971], addressed both the topside-sounder diffuse resonances (to be specific, D 1 in the present notation) and the magnetospheric "(n + 1/2)fce" emissions first reported by Kennel et al [1970] as seen in the OGO 5 data. This approach considered both the D1 resonance and the 3/2 fce magnetospheric emission in terms of the same plasma wave instability of electrostatic ECH waves in the frequency region below the upper hybrid frequency band, i.e., where the dispersion curves cover the entire range between nfc e harmonics and have shapes similar to the one in the band labeled low band 1 in Figure 2 (more bands of this type appear as O)pe/O)ce increases [Crawford, 1965] The Qn emissions were attributed to an incoherent process involving a near-Maxwellian plasma distribution with a small population of non thermal high-energy electrons.…”

Section: Introductionmentioning

confidence: 99%

An interpretation of banded magnetospheric radio emissions

Benson¹,

Osherovich²,

Fainberg³

et al. 2001

Abstract. Recently published Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) banded magnetospheric emissions, commonly referred to as "(n + 1/2)fee" emissions, where fee is the electron gyrofrequency, are analyzed by treating them as analogous to sounder-stimulated ionospheric emissions. We show that both individual spectra of magnetospheric banded emissions and a statistically derived spectra observed over the 2-year lifetime of the mission can be interpreted in a self-consistent manner. The analysis, which predicts all spectral peaks within 4% of the observed peaks, interprets the higher-frequency emissions as due to low group velocity Bernsteinmode waves and interprets the lower-frequency emissions as eigenmodes of cylindrical-electromagnetic plasma oscillations. The demarcation between these two classes of emissions is the electron plasma frequency fpe where an emission is often observed. This fpe emission is not necessarily the strongest. None of the observed banded emissions were attributed to the upper hybrid frequency. We present Alouette 2 and ISIS 1 plasma resonance data and model electron temperature (Te) values to support the argument that the frequency spectrum of ionospheric sounder-stimulated emissions is not strongly temperature dependent and thus that the interpretation of these emissions in the ionosphere is relevant to other plasmas (such as the magnetosphere) where N e and T e can be quite different but where the ratio fpe/fee is identical. The N e values deduced from the spectral interpretation do not agree with the values determined from the AMPTEB_RM three-dimensional plasma instrument. The latter, which represent a lower •ound, are found to be higher than the former by a factor of 3.2 -3.5. All values were less than 1 cm-, a domain known for measurement difficulties. One possible explanation is that the wave and plasma techniques respond to different components of a non-Maxwellian magnetospheric electron distribution.