First multipoint in situ observations of electron microbursts: Initial results from the NSF FIREBIRD II mission

Crew, A. B.; Spence, H. E.; Blake, J. B.; Klumpar, D. M.; Larsen, B.; O’Brien, T. P.; Driscoll, Stephanie C.; Handley, Matthew; Legere, Jason S.; Longworth, S.; Mashburn, K.; Mosleh, Ehson; Ryhajlo, Nicholas; Smith, S. S.; Springer, Larry; Widholm, M.

doi:10.1002/2016ja022485

Cited by 75 publications

(96 citation statements)

References 46 publications

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“…After the main phase ends, the convection electric field and substorm activity subside. Since chorus waves are linked to causing microbursts (Breneman et al, 2017;Crew et al, 2016), understanding the source, spatial extent, and power of recovery phase chorus is important to understanding radiation belt dynamics. Chorus waves are generated via the instability created by the temperature anisotropy of these hot electrons, and we present evidence that the spatial location of chorus wave power follows the changing access and drift history of these source electrons.…”

Section: Discussionmentioning

confidence: 99%

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

et al. 2019

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Whistler mode chorus waves influence the dynamics of the Earth's radiation belts and the inner magnetosphere through gyroresonant wave particle interactions. Chorus waves are generated by anisotropic hot electrons from a few to tens of keV, called source electrons, which have increased access from the nightside plasma sheet to the inner magnetosphere during geomagnetic storms. The primary drivers of geomagnetic storms are coronal mass ejections (CMEs) and corotating interaction regions (CIRs). Through differences in their characteristic physical parameters, they can each impact the nightside plasma sheet differently. Using Van Allen Probes observations, we have conducted a superposed epoch analysis of chorus wave activity and source electron development across all local times between L = 2–6 during 25 CME‐ and 35 CIR‐driven storms. The superposed epoch analysis shows that chorus wave power follows the storm phase‐dependent access of the source electron population. Chorus waves and source electrons are observed on the dawnside during the main phase, when open drift path access via eastward convective drift from the plasma sheet is enhanced. During the recovery phase, chorus waves and source electrons are observed at all magnetic local times with low intensities, exemplifying the formation of a weak symmetric, trapped electron population. A linear theory approximation for wave growth from source electron observations shows that increased wave growth follows the enhanced source electrons during each storm phase. CME and CIR storms display similar behavior and levels of average wave power; however, chorus wave activity reaches lower L‐shells during CME storms on average.

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Section: Discussionmentioning

confidence: 99%

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

et al. 2019

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“…[, ])—and to process the spatial scale of τ decay. These scales presumably determine spatial and temporal parameters for discrete localized pulsating auroral events [ Nishimura et al ., , ] and microburst precipitation events [ Crew et al ., ], if such events are driven by chorus waves.…”

Section: Introductionmentioning

confidence: 98%

Chorus whistler wave source scales as determined from multipoint Van Allen Probe measurements

Agapitov

Blum

Mozer

et al. 2017

Geophysical Research Letters

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Whistler mode chorus waves are particularly important in outer radiation belt dynamics due to their key role in controlling the acceleration and scattering of electrons over a very wide energy range. The key parameters for both nonlinear and quasi‐linear treatment of wave‐particle interactions are the temporal and spatial scales of the wave source region and coherence of the wave field perturbations. Neither the source scale nor the coherence scale is well established experimentally, mostly because of a lack of multipoint VLF waveform measurements. We present an unprecedentedly long interval of coordinated VLF waveform measurements (sampled at 16384 s−1) aboard the two Van Allen Probes spacecraft—9 h (0800–1200 UT and 1700–2200 UT) during two consecutive apogees on 15 July 2014. The spacecraft separations varied from about 100 to 5000 km (mostly radially); measurements covered an L shell range from 3 to 6; magnetic local time 0430–0900, and magnetic latitudes were ~15 and ~5° during the two orbits. Using time‐domain correlation techniques, the single chorus source spatial extent transverse to the background magnetic field has been determined to be about 550–650 km for upper band chorus waves with amplitudes less than 100 pT and up to 800 km for larger amplitude, lower band chorus waves. The ratio between wave amplitudes measured on the two spacecraft is also examined to reveal that the wave amplitude distribution within a single chorus element generation area can be well approximated by a Gaussian exp(−0.5 · r2/r02), with the characteristic scale r0 around 300 km. Waves detected by the two spacecraft were found to be coherent in phase at distances up to 400 km.

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“…However, precise measurements of the electron precipitation characteristics are not easy to make [e.g., Rodger et al , ; Nesse Tyssøy et al ., ; Crew et al , ]. There are three main techniques that are used: satellite detectors, high‐altitude balloon‐lofted platforms, and ground‐based instrumentation.…”

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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First multipoint in situ observations of electron microbursts: Initial results from the NSF FIREBIRD II mission

Cited by 75 publications

References 46 publications

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

Chorus whistler wave source scales as determined from multipoint Van Allen Probe measurements

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

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