Evidence of Sub‐MeV EMIC‐Driven Trapped Electron Flux Dropouts From GPS Observations

Hendry, Aaron T.; Rodger, Craig J.; Clilverd, Mark A.; Morley, S.

doi:10.1029/2021gl092664

Cited by 10 publications

(19 citation statements)

References 55 publications

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“…In our investigations of the GPS data, we use Roederer's generalized L-parameter L* as opposed to McIlwain's L, calculated using SpacePy with a Tsyganenko-2005 magnetic field and the LANLstar neural network model (Hendry et al, 2021;Morley et al, 2011Morley et al, , 2019Yu et al, 2012).…”

Section: Gps Particle Observationsmentioning

confidence: 99%

“…One example of this approach is the use of superposed epoch analysis to focus electron flux decreases termed “dropouts,” seen in GPS data, following high speed streams (Morley et al., 2010), and subsequently examined using low‐Earth POES observations (Meredith et al., 2011, Hendry et al., 2012). The value of similar approaches has been demonstrated more recently in multiple studies, examples being: using Van Allen Probes to investigate the impact of differing drivers (Katsavrias, Daglis, & Li, 2019) and separating adiabatic and nonadiabatic effects (Murphy et al., 2018), MLT‐resolved dynamics using POES measurements around substorm cluster events (Rodger et al., 2019), GPS‐measured changes in electron fluxes during EMIC scattering events (Hendry et al., 2021), and BD‐IES observed electron flux variations during high speed streams (Yin et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

“…demonstrated more recently in multiple studies, examples being: using Van Allen Probes to investigate the impact of differing drivers (Katsavrias, Daglis, & Li, 2019) and separating adiabatic and nonadiabatic effects (Murphy et al, 2018), MLT-resolved dynamics using POES measurements around substorm cluster events (Rodger et al, 2019), GPS-measured changes in electron fluxes during EMIC scattering events (Hendry et al, 2021), and BD-IES observed electron flux variations during high speed streams (Yin et al, 2019).…”

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confidence: 99%

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Examination of Radiation Belt Dynamics During Substorm Clusters: Activity Drivers and Dependencies of Trapped Flux Enhancements

et al. 2022

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It has long been recognized that electron fluxes in the outer radiation belt are highly dynamic. This high dynamism is thought to be due to competing drivers causing acceleration, loss, and transport, with growing evidence regarding the importance of nonlinear processes (see, e.g., the review, Ripoll et al., 2020). Typically, the occurrence and magnitude of the differing drivers are dependent upon distance from the Earth (expressed, e.g., through the L-shell), particularly due to the changing cold plasma density and the strong gradients around the plasmapause. At the same time, these driving processes also depend very strongly on magnetic local time (MLT). The drive to understand the spatial and temporal dynamism of the outer radiation belts encapsulates the primary science questions around that physical system.A long-term focus for the radiation belt physics has been predicting the variation of trapped energetic and relativistic electron fluxes by understanding the physical processes driving the rapid, large magnitude changes seen in experimental data. About 15 years ago it was common for the community to try and understand changes occurring during very large geomagnetic disturbances, often looking at times around very large Dst changes. Unfortunately, this hampered deeper physical understanding of the processes occurring in the radiation belts, due to the combination of multiple large amplitude drivers competing during such large storms (Reeves et al., 2003). This focus on case studies during the largest disturbances has been described as the "Dst mistake" (Denton et al., 2009;, summarized by Geoff Reeves with the expression "If you have seen one storm, you have seen one storm" (Koskinen, 2011, p. 323). Following the "Dst mistake," there has been a stronger focus on trying to understand the "typical" or "consistent" variations in trapped fluxes when processes occur. One example of this approach is the use of superposed epoch analysis to focus electron flux decreases termed "dropouts," seen in GPS data, following high speed streams , and subsequently examined using low-Earth POES observations (Meredith et al., 2011, Hendry et al., 2012. The value of similar approaches has been

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Section: Gps Particle Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Examination of Radiation Belt Dynamics During Substorm Clusters: Activity Drivers and Dependencies of Trapped Flux Enhancements

et al. 2022

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“…EMIC waves play an important role in radiation belt dynamics (e.g., Capannolo et al, 2018;Thorne, 2010;Yu et al, 2022). They can not only resonate with tens of keV protons but also cause efficient pitch angle scattering loss of MeV electrons (Kurita et al, 2018;Ma et al, 2015Ma et al, , 2019Meredith et al, 2003;Miyoshi et al, 2008;Shoji et al, 2011;Shprits et al, 2017;Thorne et al, 2006;Thorne & Kennel, 1971;Tian et al, 2022;Usanova et al, 2014), as well as sub-MeV electrons (Capannolo et al, 2019(Capannolo et al, , 2021Hendry et al, 2017Hendry et al, , 2019Hendry et al, , 2021. Enhancements in solar wind dynamic pressure can increase the temperature anisotropy of ring current protons through magnetospheric compression, which may excite EMIC waves (Anderson & Hamilton, 1993;Jun et al, 2021;Keika et al, 2013;Remya et al, 2018;Usanova et al, 2008;Xue et al, 2021;Yue et al, 2011Yue et al, , 2016.…”

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confidence: 99%

Prompt Appearance of Large‐Amplitude EMIC Waves Induced by Solar Wind Dynamic Pressure Enhancement and the Subsequent Relativistic Electron Precipitation

et al. 2023

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Electromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron dynamics. In this study, we find a large‐amplitude EMIC wave event induced by the prompt enhancement of solar wind dynamic pressure on 6 November 2015. These large‐amplitude EMIC waves are simultaneously observed by multiple satellites over 13 hr in magnetic local time (MLT) with a peak amplitude of ∼4 nT. Satellites at different locations observed different bands of EMIC waves, implying the importance of background plasma density in EMIC wave generation. Electron pitch angle distributions show obvious responses to EMIC wave activities. During EMIC wave appearance, the fluxes of relativistic electrons with pitch angles around 90° increase, while the fluxes of field‐aligned relativistic electrons decrease, showing distinct “bite‐out” signatures, indicating pitch angle scattering by EMIC waves, and the scattering efficiency depends on the amplitude and polarization of EMIC waves. Combined with phase space density profiles of electrons that are nearly constant at energies below the minimum resonant energy of electrons (Emin) but show dropout at energies above the Emin after EMIC wave activities, we conclude that large‐amplitude EMIC waves can cause rapid electron loss down to several hundred keV. In addition, simultaneous observations of hundreds of keV electron precipitation and tens of keV proton precipitation by Polar Operational Environmental Satellites near the region where EMIC waves are observed, provide direct evidence of relativistic electron precipitation caused by the large‐amplitude EMIC waves, ultimately driven by solar wind structures.

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“…EMIC waves have been observed as possible causes of relativistic (MeV) electron pitch angle scattering (e.g., Bortnik et al, 2006;Sigsbee et al, 2020) and subsequent precipitation into the atmosphere (e.g., Qin et al, 2018;Rodger et al, 2015). More recent studies provide evidence of sub-MeV EMIC precipitation (Blum et al, 2015;Clilverd et al, 2015;Hendry et al, 2017Hendry et al, , 2021Hendry et al, , 2019, suggesting that EMIC scattering is not exclusive to MeV energies, but act over a larger range. However, there are studies providing evidence that EMIC activity can be enhanced without subsequent precipitation (e.g., Engebretson et al, 2015;Usanova et al, 2014).…”

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confidence: 99%

Statistical Comparison of Electron Loss and Enhancement in the Outer Radiation Belt During Storms

et al. 2022

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The near‐relativistic electron population in the outer Van Allen radiation belt is highly dynamic and strongly coupled to geomagnetic activity such as storms and substorms, which are driven by the interaction of the magnetosphere with the solar wind. The energy, content, and spatial extent of electrons in the outer radiation belt can vary on timescales of hours to days, dictated by the continuously evolving influence of acceleration and loss processes. While net changes in the electron population are directly observable, the relative influence of different processes is far from fully understood. Using a continuous 12 year data set from the Proton Electron Telescope on board the Solar Anomalous Magnetospheric Particle Explorer, we statistically compare the relative variations of trapped electrons to those in the bounce loss cone (BLC). Our results show that there is a proportional increase in flux entering the BLC outside the plasmapause during storm main phase and early recovery phase. Loss enhancement is sustained on the dawnside throughout the recovery phase while loss on the duskside is enhanced around minimum Sym‐H and quickly diminishes. Spatial variations are also examined in relation to geomagnetic activity, making comparisons to possible causal wave modes such as whistler‐mode chorus and plasmaspheric hiss.

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Evidence of Sub‐MeV EMIC‐Driven Trapped Electron Flux Dropouts From GPS Observations

Cited by 10 publications

References 55 publications

Examination of Radiation Belt Dynamics During Substorm Clusters: Activity Drivers and Dependencies of Trapped Flux Enhancements

Examination of Radiation Belt Dynamics During Substorm Clusters: Activity Drivers and Dependencies of Trapped Flux Enhancements

Prompt Appearance of Large‐Amplitude EMIC Waves Induced by Solar Wind Dynamic Pressure Enhancement and the Subsequent Relativistic Electron Precipitation

Statistical Comparison of Electron Loss and Enhancement in the Outer Radiation Belt During Storms

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