An interpretation of banded magnetospheric radio emissions

Abstract

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.

Enhanced high‐altitude polar cap plasma and magnetic field values in response to the interplanetary magnetic cloud that caused the great storm of 31 March 2001: A case study for a new magnetospheric index

“…They were determined simultaneously both on the disturbed day of 31 March and, as a point of comparison, on the quiet day of 30 March. As in the work of Benson et al [2001], we stress the importance of the nondimensional magnetospheric parameter f pe / f ce . Our goal is to relate this parameter to a new nondimensional heliospheric index, i.e., the solar wind QI [ Osherovich et al , 1999b], in order to characterize the impact of a magnetic cloud on the magnetosphere.…”

“…The difficulty in making reliable magnetospheric N e measurements is well known, particularly under low‐density conditions, e.g., N e < 1 cm −3 , as has been summarized in section 5 of Benson et al [2001]. Here we determine N e from accurate measurements of the electron plasma frequency f pe , i.e., within a few percent, during active Radio Plasma Imager (RPI) resonance soundings from the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) satellite [ Burch , 2000] as described by [ Benson et al , 2003] …”

CLUSTER and IMAGE: New Ways to Study the Earth’s Plasmasphere

“…The figure shows that the model f ce delimits the upper frequency extant of the low frequency whistler noise band. Also visible are multiple n + 1 2 emission bands (Benson et al 2001) between the continuum edge and the whistler noise band, which occur at approximately (n + 1 2 )f ce where n = 1, 2, . .…”

One-dimensional particle-in-cell simulations of electrostatic Bernstein waves in plasmas with kappa velocity distributions

“…These emissions are generally attributed to electron Bernstein waves, although alternative interpretations exist. 5 On the other hand, enhanced magnetic and electric field fluctuations at frequencies between the ion cyclotron and lower hybrid frequencies, at propagation directions nearly perpendicular to the magnetic field, are also observed near the equatorial plane of the terrestrial magnetosphere. These enhanced fluctuations were initially referred to as equatorial noise, 6 but more recently, have been termed as magnetosonic waves, 7,8 or more appropriately, for low proton beta b p ( 1, are described by the ion Bernstein instability.…”