Simultaneous Observations of Electromagnetic Ion Cyclotron (EMIC) Waves and Pitch Angle Scattering During a Van Allen Probes Conjunction

Abstract

On 22 December 2015, the two Van Allen Probes observed two sets of electromagnetic ion cyclotron (EMIC) wave bursts during a close conjunction when both Probe A and Probe B were separated by 0.57 to 0.68 R E . The EMIC waves occurred during an active period in the recovery phase of a coronal mass ejection-driven geomagnetic storm. Both spacecraft observed EMIC wave bursts that had similar spatial structure within a 1-2 min time delay. The EMIC waves occurred outside the plasmasphere, within ΔL ≈ 1-2 of the plasmapause and within a few degrees in magnetic latitude of the equatorial plane. The spatial structure of the EMIC wave bursts may have been related to the proton drift paths outside the plasmasphere and influenced by total magnetic field strength variations associated with solar wind pressure enhancements. The EMIC waves were observed in a narrow L shell region from L ≈ 4.55-5.32 between 10 and 11 magnetic local time (MLT) on the outbound halves of the spacecraft orbits and from L ≈ 4.82-5.51 between 13 and 14 MLT on the inbound halves of the spacecraft orbits. However, Pc1 pulsations were observed on the ground over a broad range of local times. The anisotropy of the proton pitch angle distributions was enhanced when the EMIC waves were observed. Although the overall radiation belt response during this storm was dominated by acceleration and transport processes, the EMIC waves produced local pitch angle scattering of 13-15 keV protons and 2.1-2.6 MeV electrons, consistent with calculations of the expected resonant energies.

On the Impacts of Ions of Ionospheric Origin and Their Composition on Magnetospheric EMIC Waves

“…Observational evidence of relativistic electron precipitation in association with EMIC waves has been reported by an increasing number of recent studies (e.g. Rodger et al, 2008;Li et al, 2014;Blum et al, 2015;Blum et al, 2019;Lessard et al, 2019;Qin et al, 2019;Sigsbee et al, 2020;Kim et al, 2021). However, the cold plasma approximation may fail near the He + gyrofrequency, and the warm plasma effect of He + ions on wave growth should be considered.…”

Sensitive Dependence of Ultrarelativistic Electron Precipitation on EMIC Wave Frequency

“…Electromagnetic ion cyclotron (EMIC) waves have long been known to be amplified by energetic (a few to a few tens of keV) ions with , where refer to the ion perpendicular and parallel temperatures relative to the background magnetic field, respectively (Cornwall 1965; C. F. Kennel & Petschek 1966). Recent studies (e.g., J. H. Cho et al., 2017, 2016; Noh et al., 2018; Remya et al., 2018; Sigsbee et al., 2020) have confirmed that substorm injections and solar wind dynamic pressure enhancements can provide an anisotropic ion distribution that is suitable for triggering EMIC waves in the inner magnetosphere.…”

“…F. Kennel & Petschek 1966). Recent studies (e.g., J. H. Cho et al, 2017Cho et al, , 2016Noh et al, 2018;Remya et al, 2018;Sigsbee et al, 2020) have confirmed that substorm injections and solar wind dynamic pressure enhancements can provide an anisotropic ion distribution that is suitable for triggering EMIC waves in the inner magnetosphere.…”

ULF Wave Modeling, Effects, and Applications: Accomplishments, Recent Advances, and Future

“…A few examples of recent advances in EMIC wave research include significantly improved data coverage and statistics (e.g., Allen et al, 2016;Sigsbee et al, 2016Sigsbee et al, , 2020Wang et al, 2017;Engebretson et al, 2018;Lee et al, 2019;Vines et al, 2019Vines et al, , 2021Grison et al, 2021;Jun et al, 2021), investigation of the association of the EMIC waves with injections (e.g., Remya et al, 2018;Jun et al, 2019;Kim et al, 2021), improved understanding of EMIC wave generation (e.g., Lee et al, 2021), exploration of the possibility of sub-MeV electron scattering (e.g., Zhang X. J. et al, 2019;Capannolo et al, 2019;Denton et al, 2019) and quantifying their effect in modeling (e.g., Ma et al, 2016;Drozdov et al, 2017;Cervantes et al, 2020;Wang D. et al, 2020;Drozdov et al, 2020).…”