Statistics of Magnetosonic Waves in the Slot Region Observed by Van Allen Probes

Abstract

The slot region, normally located at L = 1.8-3.0 and separating the Earth's inner and outer radiation belts, can be highly dynamic during geomagnetically disturbed periods (Lyons & Thorne, 1973;Meredith et al., 2007). Many previous studies have focused on various physical processes including the evolution of pitch angle distributions (PADs) (Zhao et al., 2014a(Zhao et al., , 2014b, the pitch angle scattering loss (e.g., Hua et al., 2021;Summers et al., 2007;Zhu et al., 2021) and diffusive transports of energetic electrons (Ma et al., 2017) in the slot region. Various plasma waves have been involved in the slot region electron dynamics, such as ULF waves, plasmaspheric hiss, VLF transmitter signals, lightning-generated whistlers, and magnetosonic (MS) waves (

Magnetosonic Waves Above the Lower Hybrid Frequency in Cyclotron Resonance With the Van Allen Radiation Belt Electrons

“…Following strong substorms (SME* > 400 nT), all of the L‐MLT bins with wave amplitudes of 10–30 pT are inside the plasmasphere. The average amplitude of the f > f lh magnetosonic waves is approximately five times smaller than that of the f < f lh magnetosonic waves (Kim & Shprits, 2018; Ma et al., 2019; Teng et al., 2019; Yan et al., 2021). The SME*‐dependence and MLT‐dependence of magnetosonic waves imply that they could be generated by westward drifting protons injected during substorms.…”

“…First, waves with sufficiently strong power spectral densities P B > 10 −8 nT 2 Hz −1 , large normal angles ψ > 75°, and high planarities F B > 0.7 are identified as candidate magnetosonic waves. These criteria are comparable to those used in previous magnetosonic wave statistics (Ma et al, 2019;Teng et al, 2019;Yan et al, 2021). Next, the candidate waves significantly deviating from the theoretical predictions are removed.…”

“…The average amplitude of the f > f lh magnetosonic waves is approximately five times smaller than that of the f < f lh magnetosonic waves (Kim & Shprits, 2018; Vertical dashed lines mark the proton cyclotron frequency f cp and the lower hybrid frequency f lh . Ma et al, 2019;Teng et al, 2019;Yan et al, 2021). The SME*-dependence and MLT-dependence of magnetosonic waves imply that they could be generated by westward drifting protons injected during substorms.…”

“…In contrast to previous statistical studies of magnetosonic waves below f lh (Ma et al., 2013, 2019; Meredith et al., 2008; Němec et al., 2013; Santolík et al., 2004; Teng et al., 2019; Tsurutani et al., 2014; Yan et al., 2021), we focus on the spatiotemporal distribution of magnetosonic waves above f lh . The ambient electron density (Kurth et al., 2015), magnetic field strength, and wave electromagnetic spectral matrix were acquired by the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS; Kletzing et al., 2013) suite onboard the Van Allen Probes mission (Mauk et al., 2013) from November 2012 to July 2019.…”

Electron Lifetimes Measured at LEO: Comparison With RBSP Estimates and Pitch Angle Resolved Lifetimes

“…Fung et al (2006) suggested that the most efficient wave-particle interactions occur off the magnetic equator in the slot region, however more recent studies investigating the individual wave modes responsible for the slot region have found varying results. Magnetosonic waves are typically located near the magnetic equator at |λ m | < 5° (e.g., Ma et al, 2013;Yan et al, 2021). Meredith et al (2018) found that the latitudinal distribution of plasmaspheric hiss intensity has two peaks: one at the magnetic equator and one at high magnetic latitudes (λ m ∼ 40°-50°) with a deep minimum in between.…”