Survey of magnetosonic waves and proton ring distributions in the Earth's inner magnetosphere

Abstract

[1] Fast magnetosonic waves can lead to the local acceleration of electrons from $10 keV up to a few MeV on a timescale of 1-2 d and may play an important role in radiation belt dynamics. Here we present a survey of wave and particle data from the Combined Release and Radiation Effects Satellite (CRRES) to determine the global morphology of the waves as a function of magnetic activity, and to investigate the role of proton rings as a potential source mechanism. The intensity of fast magnetosonic waves in the frequency range 0.5 f LHR < f < f LHR increases with increasing magnetic activity suggesting they are related to periods of enhanced convection and/or substorm activity. They are observed at most magnetic local times (MLT) outside the plasmapause but are restricted to the dusk sector inside the plasmapause. The MLT distribution of low energy proton rings (E R < 30 keV) with energies exceeding the Alfvén energy (E R > E A ) required for instability closely matches the distribution of magnetosonic waves on the dusk side, both inside and outside the plasmapause, suggesting that low energy proton rings are a likely source of energy driving the waves. However, intense magnetosonic waves are also observed outside the plasmapause on the dawn-side that do not satisfy (E R > E A ). Although proton rings with E R > 30 keV could drive the instabilities, the source of these waves is yet to be properly identified. Since fast magnetosonic waves can accelerate electrons we suggest that they may provide a significant energy transfer process between the ring current and the outer electron radiation belt.

Multiple harmonic ULF waves in the plasma sheet boundary layer: Instability analysis

“…/T k is reduced to unity for each component, showing that the instability is not driven by the temperature anisotropy, but by the ring-like distribution. Note that equatorial magnetosonic waves [Meredith et al, 2008] at harmonics of W cp are also thought to be driven by a ring-like distribution function. But those waves are predominantly compressional (C B = (dB k ) 2 /(dB) 2 close to unity).…”

Effect of plasma density on diffusion rates due to wave particle interactions with chorus and plasmaspheric hiss: extreme event analysis

“…Interaction between plasmaspheric hiss and energetic electrons is a major loss process inside the plasmapause for electron energies from 0.1 to a few MeV (Lyons and Thorne, 1973;Meredith et al, 2007Meredith et al, , 2009. Magnetosonic waves may also be an important acceleration mechanism Meredith et al, 2008Meredith et al, , 2009Mourenas et al, 2013) and EMIC waves may be an important loss mechanism for MeV electrons Meredith et al, 2003;Jordanova et al, 2008). However, the roles of magnetosonic and EMIC waves in relativistic electron dynamics has yet to be fully assessed, and are not considered further here.…”

Interactions between magnetosonic waves and radiation belt electrons: Comparisons of quasi‐linear calculations with test particle simulations

“…Both observations [Meredith et al, 2008] and simulations [Chen et al, 2010;Liu et al, 2011;Ma et al, 2014] have shown that such equatorial MS waves are preferentially excited by proton ring distributions. The signatures of MS waves include their low ellipticity, which leads to nearly linear polarization, and their nearly perpendicular propagation, which results in much stronger E ⟂ and B ∥ components compared to E ∥ and B ⟂ components, respectively .…”