Tunneling and mode conversion of fast magnetosonic waves in the magnetospheres of Earth and Mercury

TL;DR

This paper investigates how mode conversion of fast magnetosonic waves in Earth and Mercury's magnetospheres can be used to determine heavy ion concentrations by analyzing resonant wave structures and their efficiency.

Contribution

It identifies conditions for maximum mode conversion efficiency and proposes a method to infer heavy ion concentrations from observed wave spectra.

Findings

Maximized mode conversion occurs under specific plasma conditions.

Resonant wave frequencies reveal heavy ion concentrations.

Method enables remote sensing of magnetospheric plasma composition.

Abstract

Narrow-band linearly polarized waves, having a resonant structure and a peak frequency between the local cyclotron frequency of protons and heavy ions, have been detected in the magnetospheres of Earth and of Mercury. Some of these wave events have been suggested to be driven by linear mode conversion (MC) of the fast magnetosonic waves at the ion-ion hybrid (IIH) resonances. Since the resonant IIH frequency is linked to the plasma composition, solving the inverse problem allows one to infer the concentration of the heavy ions from the measured frequency spectra. In this paper, we identify the conditions when the MC efficiency is maximized in the magnetospheric plasmas and discuss how this can be applied for estimating the heavy ion concentration in the magnetospheres of Earth and Mercury.