BARREL observations of an ICME‐shock impact with the magnetosphere and the resultant radiation belt electron loss

Halford, A. J.; McGregor, S. L.; Murphy, K. R.; Millan, R. M.; Hudson, M. K.; Woodger, L. A.; Cattel, C. A.; Breneman, A. W.; Mann, I. R.; Kurth, W. S.; Hospodarsky, G. B.; Gkioulidou, M.; Fennell, J. F.

doi:10.1002/2014ja020873

Cited by 38 publications

(81 citation statements)

References 39 publications

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“…Since ULF wave time scales are of order minutes, we can assume that the first and second adiabatic invariants are conserved, but the third is not. Previous studies have investigated how conserving the first and second invariants affects the change in pitch angle and loss cone, under the assumption of a relatively dipolar magnetic field (e.g., Foster et al, ; Halford et al, ; Li et al, ; Wygant et al, ). For example, Halford et al () showed that the change in the equatorial pitch angle of a particle in a slowly changing and dipolar magnetic field configuration was independent of mass or energy and could be written as

sin α_{eq,f} = - \frac{L_{f}^{\frac{1}{2}} {cos}^{2} α_{eq 0}}{2 L_{0}^{\frac{1}{2}} sin α_{eq 0}} + \frac{1}{2} {(\frac{L_{f} {cos}^{4} α_{eq 0}}{L_{0} {sin}^{2} α_{eq 0}} + 4)}^{\frac{1}{2}}

where α eq0 and α eq,f are the initial and final equatorial pitch angles and L 0 and L f are the initial and final L values of the particle in dipolar L .…”

Section: What Processes Could Drive Localized Ulf‐modulated Precipitamentioning

confidence: 99%

The Role of Localized Compressional Ultra‐low Frequency Waves in Energetic Electron Precipitation

et al. 2018

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Typically, ultra‐low frequency (ULF) waves have historically been invoked for radial diffusive transport leading to acceleration and loss of outer radiation belt electrons. At higher frequencies, very low frequency waves are generally thought to provide a mechanism for localized acceleration and loss through precipitation into the ionosphere of radiation belt electrons. In this study we present a new mechanism for electron loss through precipitation into the ionosphere due to a direct modulation of the loss cone via localized compressional ULF waves. We present a case study of compressional wave activity in tandem with riometer and balloon‐borne electron precipitation across keV‐MeV energies to demonstrate that the experimental measurements can be explained by our new enhanced loss cone mechanism. Observational evidence is presented demonstrating that modulation of the equatorial loss cone can occur via localized compressional wave activity, which greatly exceeds the change in pitch angle through conservation of the first and second adiabatic invariants. The precipitation response can be a complex interplay between electron energy, the localization of the waves, the shape of the phase space density profile at low pitch angles, ionospheric decay time scales, and the time dependence of the electron source; we show that two pivotal components not usually considered are localized ULF wave fields and ionospheric decay time scales. We conclude that enhanced precipitation driven by compressional ULF wave modulation of the loss cone is a viable candidate for direct precipitation of radiation belt electrons without any additional requirement for gyroresonant wave‐particle interaction. Additional mechanisms would be complementary and additive in providing means to precipitate electrons from the radiation belts during storm times.

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sin α_{eq,f} = - \frac{L_{f}^{\frac{1}{2}} {cos}^{2} α_{eq 0}}{2 L_{0}^{\frac{1}{2}} sin α_{eq 0}} + \frac{1}{2} {(\frac{L_{f} {cos}^{4} α_{eq 0}}{L_{0} {sin}^{2} α_{eq 0}} + 4)}^{\frac{1}{2}}

where α eq0 and α eq,f are the initial and final equatorial pitch angles and L 0 and L f are the initial and final L values of the particle in dipolar L .…”

Section: What Processes Could Drive Localized Ulf‐modulated Precipitamentioning

confidence: 99%

The Role of Localized Compressional Ultra‐low Frequency Waves in Energetic Electron Precipitation

et al. 2018

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“…Two models for electron spectra were considered: the first is exponential and the second is mono‐energetic. The peaked character of the mono‐energetic energy spectrum is representative of the sort of electron precipitation spectra potentially driven by EMIC waves, using insight gained from the analysis of Van Allen Probes electron spectra, and fits to similar BARREL observations [ Millan et al , ; Li et al , ; Woodger et al , ; Halford et al , ]. Figure presents an example of model evaluation.…”

Section: Barrel Spectral Informationmentioning

confidence: 99%

“…In fact, the best fit to the BARREL X‐ray flux spectrum was a 1350 keV mono‐energetic electron spectrum. Halford et al [] used BARREL observations to study a solar wind shock event and the resultant radiation‐belt electron precipitation. Chorus wave amplitudes from Radiation Belt Storm Probes B (RBSP‐B) were used to calculate the energy‐dependent diffusion coefficients close to the bounce loss cone, which were shown to decrease by an order of magnitude for energies >100 keV.…”

Section: Introductionmentioning

confidence: 99%

Investigating energetic electron precipitation through combining ground‐based and balloon observations

et al. 2017

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A detailed comparison is undertaken of the energetic electron spectra and fluxes of two precipitation events that were observed in 18/19 January 2013. A novel but powerful technique of combining simultaneous ground‐based subionospheric radio wave data and riometer absorption measurements with X‐ray fluxes from a Balloon Array for Relativistic Radiation‐belt Electron Losses (BARREL) balloon is used for the first time as an example of the analysis procedure. The two precipitation events are observed by all three instruments, and the relative timing is used to provide information/insight into the spatial extent and evolution of the precipitation regions. The two regions were found to be moving westward with drift periods of 5–11 h and with longitudinal dimensions of ~20° and ~70° (1.5–3.5 h of magnetic local time). The electron precipitation spectra during the events can be best represented by a peaked energy spectrum, with the peak in flux occurring at ~1–1.2 MeV. This suggests that the radiation belt loss mechanism occurring is an energy‐selective process, rather than one that precipitates the ambient trapped population. The motion, size, and energy spectra of the patches are consistent with electromagnetic ion cyclotron‐induced electron precipitation driven by injected 10–100 keV protons. Radio wave modeling calculations applying the balloon‐based fluxes were used for the first time and successfully reproduced the ground‐based subionospheric radio wave and riometer observations, thus finding strong agreement between the observations and the BARREL measurements.

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“…The different time scales and energy resolution allow for observations of a wide range of precipitation events in both energy and time. Figure (top) is a spectrogram plot of BARREL slow spectra observed on 7–8 January 2014 discussed in Halford et al []. The figure shows various features in the X‐ray data that are from both electron precipitation and other sources [ Halford et al , ].…”

Section: The Barrel Mission Summarymentioning

confidence: 99%

A summary of the BARREL campaigns: Technique for studying electron precipitation

et al. 2015

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The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) studies the loss of energetic electrons from Earth's radiation belts. BARREL's array of slowly drifting balloon payloads was designed to capitalize on magnetic conjunctions with NASA's Van Allen Probes. Two campaigns were conducted from Antarctica in 2013 and 2014. During the first campaign in January and February of 2013, there were three moderate geomagnetic storms with SYM‐H min < −40 nT. Similarly, two minor geomagnetic storms occurred during the second campaign, starting in December of 2013 and continuing on into February of 2014. Throughout the two campaigns, BARREL observed electron precipitation over a wide range of energies and exhibiting temporal structure from hundreds of milliseconds to hours. Relativistic electron precipitation was observed in the dusk to midnight sector, and microburst precipitation was primarily observed near dawn. In this paper we review the two BARREL science campaigns and discuss the data products and analysis techniques as applied to relativistic electron precipitation observed on 19 January 2013.

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BARREL observations of an ICME‐shock impact with the magnetosphere and the resultant radiation belt electron loss

Cited by 38 publications

References 39 publications

The Role of Localized Compressional Ultra‐low Frequency Waves in Energetic Electron Precipitation

The Role of Localized Compressional Ultra‐low Frequency Waves in Energetic Electron Precipitation

Investigating energetic electron precipitation through combining ground‐based and balloon observations

A summary of the BARREL campaigns: Technique for studying electron precipitation

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