A. Breneman

Energetic electron injections deep into the inner magnetosphere associated with substorm activity

From a survey of the first nightside season of NASAs Van Allen Probes mission (December 2012 to September 2013), 47 energetic (tens to hundreds of keV) electron injection events were found at L shells ≤ 4, all of which are deeper than any previously reported substorm-related injections. Preliminary details from these events are presented, including how all occurred shortly after dipolarization signatures and injections were observed at higher L shells, how the deepest observed injection was at L ~ 2.5, and, surprisingly, how L ≤ 4 injections are limited in energy to ≤250 keV. We present a detailed case study of one example event revealing that the injection of electrons down to L ~ 3.5 was different from injections observed at higher L and likely resulted from electrons interacting with a fast magnetosonic wave in the Pi2 frequency range inside the plasmasphere. These observations demonstrate that injections occur at very low L shells and may play an important role for inner zone electrons.

The properties of large amplitude whistler mode waves in the magnetosphere: Propagation and relationship with geomagnetic activity

using waveform capture data from the Wind spacecraft. Weobserved 247 whistler mode waves with at least one electricfield component (105/247 had≥80 mV/m peak!to!peakamplitudes) and 66 whistler mode waves with at least onesearch coil magnetic field component (38/66 had≥0.8 nTpeak!to!peak amplitudes). Wave vectors determined fromevents with three magnetic field components indicate that30/46 propagate within 20° of the ambient magnetic field,though some are more oblique (up to ∼50°). No relationshipwas observed between wave normal angle and GSM lati-tude. 162/247 of the large amplitude whistler mode waveswere observed during magnetically active periods (AE >200 nT). 217 out of 247 total whistler mode waves exam-ined were observed inside the radiation belts. We presenta waveform capture with the largest whistler wave magneticfield amplitude (^8nTpeak!to!peak) ever reported in theradiation belts. The estimated Poynting flux magnitude asso-ciated with this wave is ^300 mW/m

Statistics of multispacecraft observations of chorus dispersion and source location

We report emission characteristics of 52 chorus events on 23 August 2003 and10 events on three other days, modeled with a ray tracing technique. Chorus waves have acharacteristic frequency/time variation that is a combination of frequency separation bypropagation dispersion and a time-dependent source frequency emission drift. A cross-correlation technique comparing data from multiple Cluster spacecraft quantifies thefrequency variation owing to propagation dispersion. The comparison of the datacross correlations with the simulated cross correlations allows the identification of acorrelation region which has at least one common point with the chorus source region.Any remaining frequency/time variation in the single-spacecraft spectrograms notaccounted for by the cross correlations is then used to determine the time-dependentsource frequency emission drift. The final modeled correlation region and sourcefrequency emission drift for each chorus event is consistent with both the cross-correlationand single-spacecraft data. The modeled correlation regions are located near the magneticequator and are, in general, more extended parallel to the Earth’s magnetic field thanperpendicular to it. It is found that waves with frequencies above and below 1/2 theequatorial electron cyclotron frequency on the magnetic field line of the spacecraft (lowerand upper band, respectively) are emitted in a broad spectrum of wave normal angles.There is also some preference for lower band waves observed at the spacecraft tohave been emitted near the Gendrin angle and at earthward-pointing wave normal anglesof between 20 and 30 . The latter result is close to the range of wave normal anglesshown recently to be connected with chorus that propagates into the plasmasphereand evolves into the incoherent plasmaspheric hiss spectrum, known to be connectedto pitch angle scattering and loss of electrons in the electron slot region. Finally, thetime-dependent source frequency emission drift for these eventsranges from 1to20 kHz/s.For most events these rates account for at least 2/3 of the chorus frequency/time variationwith the rest being due to propagation dispersion.

Observation of relativistic electron microbursts in conjunction with intense radiation belt whistler-mode waves

We present multi-satellite observations indicating a strong correlation between large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. The microburst precipitation exhibits a bursty temporal structure similar to that of the observed large amplitude wave packets, suggesting a connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave--particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

THEMIS observations of the magnetopause electron diffusion region: Large amplitude waves and heated electrons

Received 14 April 2013; revised 9 May 2013; accepted 14 May 2013; published 18 June 2013. [1 ]W e present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described byScudderet al.[2012]atthe subsolarmagnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (~30keV) within the electron diffusion region have anisotropic distributions with Te! /Tek > 1t hat may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the “X-line” along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves. Citation: Tang, X., C. Cattell, J. Dombeck, L. Dai, L. B. Wilson III, A. Breneman, and A. Hupach (2013), THEMIS observations of the magnetopause electron diffusion region: Large amplitude waves and heated electrons, Geophys. Res. Lett., 40 ,2 884‐2890, doi:10.1002/ grl.50565.

Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss.

Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high plasma density called the plasmasphere, within four to five Earth radii, arises largely from interaction with an electromagnetic plasma wave called plasmaspheric hiss. This interaction strongly influences the evolution of the radiation belts during a geomagnetic storm, and over the course of many hours to days helps to return the radiation-belt structure to its ‘quiet’ pre-storm configuration. Observations have shown that the long-term electron-loss rate is consistent with this theory but the temporal and spatial dynamics of the loss process remain to be directly verified. Here we report simultaneous measurements of structured radiation-belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated by hiss-scattered electrons colliding with the Earths atmosphere after removal from the radiation belts. Our results show that changes of up to an order of magnitude in the dynamics of electron loss arising from hiss occur on timescales as short as one to twenty minutes, in association with modulations in plasma density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. This nearly global-scale coherence was not predicted and may affect the short-term evolution of the radiation belts during active times.

Observations of electromagnetic whistler precursors at supercritical interplanetary shocks

] We present observations of electromagnetic precursorwaves, identified as whistler mode waves, at supercriticalinterplanetary shocks using the Wind search coil magneto-meter. The precursors propagate obliquely with respect tothe local magnetic field, shock normal vector, solar windvelocity, and they are not phase standing structures. All areright-hand polarized with respect to the magnetic field(spacecraft frame), and all but one are right-hand polarizedwith respect to the shock normal vector in the normal inci-dence frame. They have rest frame frequencies f

Observations of kinetic scale field line resonances

We identify electromagnetic field variations from the Van Allen Probes which have the properties of Doppler shifted kinetic scale Alfvenic field line resonances. These variations are observed during injections of energetic plasmas into the inner magnetosphere. These waves have scale sizes perpendicular to the magnetic field which are determined to be of the order of an ion gyro-radius (ρi) and less. Cross-spectral analysis of the electric and magnetic fields reveals phase transitions at frequencies correlated with enhancements and depressions in the ratio of the electric and magnetic fields. Modeling shows that these observations are consistent with the excitation of field-line resonances over a broad range of wave numbers perpendicular to the magnetic field (k⊥) extending to k⊥ρi ≫ 1. The amplitude of these waves is such that E/Bo ≳ Ωi/k⊥ (E, Bo, and Ωi are the wave amplitude, background field strength, and ion gyro-frequency, respectively) leading to ion demagnetization and acceleration for multiple transitions through the wave potential.

Storm time occurrence and spatial distribution of Pc4 poloidal ULF waves in the inner magnetosphere: A Van Allen Probes statistical study

Poloidal ULF waves are capable of efficiently interacting with energetic particles in the ring current and the radiation belt. Using Van Allen Probes (Radiation Belt Storm Probes (RBSP)) data from October 2012 to July 2014, we investigate the spatial distribution and storm time occurrence of Pc4 (7-25mHz) poloidal waves in the inner magnetosphere. Pc4 poloidal waves are sorted into two categories: waves with and without significant magnetic compressional components. Two types of poloidal waves have comparable occurrence rates, both of which are much higher during geomagnetic storms. The noncompressional poloidal waves mostly occur in the late recovery phase associated with an increase of Dst toward 0, suggesting that the decay of the ring current provides their free energy source. The occurrence of dayside compressional Pc4 poloidal waves is found correlated with the variation of the solar wind dynamic pressure, indicating their origin in the solar wind. Both compressional and noncompressional waves preferentially occur on the dayside near noon at L similar to 5-6. In addition, compressional poloidal waves are observed at magnetic local time 18-24 on the nightside. The location of the Pc4 poloidal waves relative to the plasmapause is investigated. The RBSP statistical results may shed light on the in-depth investigations of the generation and propagation of Pc4 poloidal waves.

Evidence for injection of relativistic electrons into the Earth's outer radiation belt via intense substorm electric fields

Observation and model results accumulated in the last decade indicate that substorms can promptly inject relativistic ‘killer’ electrons (≥MeV) in addition to 10–100 keV subrelativistic populations. Using measurements from Cluster, Polar, LANL, and GOES satellites near the midnight sector, we show in two events that intense electric fields, as large as 20 mV/m, associated with substorm dipolarization are associated with injections of relativistic electrons into the outer radiation belt. Enhancements of hundreds of keV electrons at dipolarization in the magnetotail can account for the injected MeV electrons through earthward transport. These observations provide evidence that substorm electric fields inject relativistic electrons by transporting magnetotail electrons into the outer radiation belt. In these two events, injected relativistic electrons dominated the substorm timescale enhancement of MeV electrons as observed at geosynchronous orbit.