Bibliography

Characteristics of Electron Precipitation During 40 Energetic Electron Injections Inferred via Subionospheric VLF Signal Propagation

Energetic electron injection events are associated with energetic electron precipitation (EEP) through possible resonant wave-particle interactions. Previous studies confirm the impacts of injection-driven precipitation on observed amplitude/phase of subionospheric VLF (very low frequency) signals transmitted from distant artificial transmitters. Currently, there are substantial uncertainties on precipitation characteristics and flux during injection events. In this work we study 40 injection events selected by Van Allen Probes particle data to investigate the changes in amplitude and phase of VLF signals at ground receivers across Canada during particle injection events. We model the ionospheric effect of the EEP flux to find its impact on VLF propagation and characterize the injection events. Typically, we find a clear phase advance of ~40° in the received VLF signal at Fort Smith (Canada, L = 8) transmitted from U.S. Navy communication transmitter NAA at Maine (USA). Comparing to other VLF transmitter-receiver paths in North America leads us to conclude that effects are only seen on paths with adequately large range ≫200 km) through L > 7. Modeling the VLF phase change indicates that in the majority of events (>90\%), less than 10\% of the strong scattering limit inferred from particle flux measurements at the Van Allen Probes is required to obtain the observed VLF phase signature. The median precipitating flux during energetic particle injections is less than 4 × 106 el/cm2 s sr (<10\% of the strong scattering rate) for electrons above ~40 keV extracted from trapped particles energy spectrum. This implies that strong scattering is not typical for these 40 selected energetic electron injection events.

Ghaffari, R.; Cully, C.; Turner, D.; Reeves, G.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2019JA027233

Van Allen Probes

Correlated Pc4-5 ULF waves, whistler-mode chorus and pulsating aurora observed by the Van Allen Probes and ground-based systems

Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch-angle scattering of 10\textquoterights keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and 10\textquoterights keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4-5 compressional pulsations and modulation of whistler-mode chorus using THEMIS. In the current study, we present simultaneous in-situ observations of structured chorus waves and an apparent field line resonance (in the Pc4-5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4-5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth\textquoterights atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. Such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades, and may be a result of nonlinear chorus wave interactions in the equatorial region.

Jaynes, A.; Lessard, M.; Takahashi, K.; Ali, A.; Malaspina, D.; Michell, R.; Spanswick, E.; Baker, D.; Blake, J.; Cully, C.; Donovan, E.; Kletzing, C.; Reeves, G.; Samara, M.; Spence, H.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 07/2015

YEAR: 2015     DOI: 10.1002/2015JA021380

aurora; precipitation; pulsating aurora; substorms; ULF waves; Van Allen Probes; VLF waves

Wave normal angles of whistler-mode chorus rising and falling tones

We present a study of wave normal angles (θk) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (\textpm20\textdegree), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-θk histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/fc,e≈0.5 (f is the chorus frequency, fc,e is the local electron cyclotron frequency) and at θk\~40\textdegree. Below θk\~40\textdegree, the average value for θk is predominantly field aligned, but slightly increasing with frequency toward half of fc,e (θk up to 20\textdegree). Above half of fc,e, the average θk is again decreasing with frequency. Above θk\~40\textdegree, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for θk>40\textdegree and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at θk>40\textdegree, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane.

Taubenschuss, Ulrich; Khotyaintsev, Yuri; ik, Ondrej; Vaivads, Andris; Cully, Christopher; Le Contel, Olivier; Angelopoulos, Vassilis;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014JA020575

Chorus; wave normal

The Electric Field and Waves (EFW) Instruments on the Radiation Belt Storm Probes Mission

The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by \~15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the \textquotedbllefthighest quality\textquotedblright events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).

Wygant, J.; Bonnell, J; Goetz, K.; Ergun, R.E.; Mozer, F.; Bale, S.D.; Ludlam, M.; Turin, P.; Harvey, P.R.; Hochmann, R.; Harps, K.; Dalton, G.; McCauley, J.; Rachelson, W.; Gordon, D.; Donakowski, B.; Shultz, C.; Smith, C.; Diaz-Aguado, M.; Fischer, J.; Heavner, S.; Berg, P.; Malaspina, D.; Bolton, M.; Hudson, M.; Strangeway, R.; Baker, D.; Li, X.; Albert, J.; Foster, J.C.; Chaston, C.C.; Mann, I.; Donovan, E.; Cully, C.M.; Cattell, C.; Krasnoselskikh, V.; Kersten, K.; Brenneman, A; Tao, J.;

Published by: Space Science Reviews      Published on: 11/2013

YEAR: 2013     DOI: 10.1007/s11214-013-0013-7

RBSP; Van Allen Probes