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We analyze continuous multi-point measurements of electromagnetic field waveforms onboard the Cluster spacecraft in order to contribute to the discussion on sources of plasmaspheric hiss, known as ...

Electron cyclotron harmonic (ECH) and whistler chorus waves are recognized as the two mechanisms responsible for the resonant wave‐particle interactions necessary to precipitate plasma sheet electrons into the ionosphere, producing the diffuse Aurora. Previous work has demonstrated ECH waves dominate electron scattering at L shells >8, while whistler chorus dominates scattering at L shells L 1, consistent with electron betatron acceleration. Here, however, we find whistler chorus emissions throughout an interval of fast flows where Te,⊥/Te,||< 1. Parallel electron beams account for the enhanced parallel electron temperature and serve as the instability mechanism for the whistler chorus. The parallel electron beams and associated cigar‐shaped distributions are consistent with Fermi acceleration at dipolarizations in fast flows. We demonstrate that the scattering efficiency of the whistler chorus exceeds that of ECH waves, which THEMIS also detects during the fast flows. The obliquity of the whistler waves permits efficient scattering of lower‐energy electrons into the diffuse aurora. We conclude that Fermi acceleration of electrons provides one important free‐energy source for the wave‐particle interactions responsible for coupling plasma sheet electrons into the diffuse aurora during substorm conditions.

International audience; For the first time an evaluation of the whistler rate around the Earth is performed using results from the neural network aboard the microsatellite DEMETER. It is shown that the rate of whistlers with low dispersion calculated all around the Earth as a function of longitude vary between 1 and 6 s−1 during nighttime (22.30 LT) and between 0.5 and 0.7 s−1 during daytime (10.30 LT). The whistler rate is anticorrelated with the F10.7‐cm solar flux. A decrease by 25% of the solar flux corresponds to an increase of 62% (26%) of the averaged whistler rate calculated for the entire Earth during nighttime (daytime). Using this averaged whistler rate, the global lightning rate is estimated to be of the order of 123 s−1 (27 s−1) during nighttime (daytime). The main conclusion concerns the precipitation of the electrons in the radiation belt by interaction with the whistlers. It is shown that the decrease of the lightning activity at solar minimum (shown with the help of the Schumann resonances) is largely counterbalanced by the increase of the whistler rates in the upper part of the ionosphere due to the decrease of the ionospheric absorption.

The temporal variation of the energetic electron flux distribution caused by whistler mode chorus waves through the cyclotron resonant interaction provides crucial information on how electrons are ...

With a linear theoretical model, we have investigated the properties of whistler waves excited by anisotropic hot electrons with a drift velocity, which is usually neglected in previous studies. It...

Whether or not coherent magnetospheric whistler waves play important roles in the pitch‐angle scattering of energetic particles is a crucial question in magnetospheric physics. The interaction of a thermal distribution of energetic particles with coherent whistler waves is thus investigated. The distribution is prescribed by the Maxwell‐Juttner distribution, which is a relativistic generalization of the Maxwell‐Boltzmann distribution. Coherent whistler waves are modeled by circularly polarized waves propagating parallel to the background magnetic field. It is shown that for parameters relevant to magnetospheric chorus, a significant fraction (1‐5%) of the energetic particle population undergoes drastic, non‐diffusive pitch‐angle scattering by coherent chorus. The scaling of this fraction with the wave amplitude may also explain the association of relativistic microbursts to large‐amplitude chorus. A much improved condition for large pitch‐angle scattering is presented that is related to, but may or may not include the exact resonance condition depending on the particle's initial conditions. The theory reveals a critical mechanism not contained in the widely‐used second‐order trapping theory.

VLF spectrograms registered at Kannuslehto ground station, after cleaning them from strong sferics, reveal VLF noise suppression by whistlers and whistler echo trains, which consists in significant...

Continuous burst mode VLF measurements were recorded on the RBSP/Van Allen Probes satellites and are analyzed to detect pulses from the Russian Alpha (RSDN-20) ground-based navigational system. Based on the wave characteristics of these pulses and on the position of the spacecraft, the signals propagated mostly in ducted mode in the plasmasphere. Knowledge of the propagation path allowed us to carry out a monochromatic wave propagation inversion to obtain plasmaspheric electron densities. We compared the obtained densities with independent in-situ measurements on the spacecraft. The results show good agreement, validating our inversion process. This contributes to validating the field-aligned density profile model routinely used in the inversion of whistlers detected on the ground. Furthermore, our method can provide electron densities at regimes where no alternative measurements are available on the spacecraft. This raises the possibility of using this method as an additional tool to measure and monitor plasmaspheric electron densities., Comment: 21 pages, 5 figures, accepted by Journal of Geophysical Research

We investigate the influence of lightning‐generated whistlers on the overall intensity of electromagnetic waves measured by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions spacecraft (2004–2010, quasi Sun‐synchronous polar orbit with an altitude of about 700 km) at frequencies below 18 kHz. Whistler occurrence rate evaluated using an onboard neural network designed for automated whistler detection is used to distinguish periods of high and low whistler occurrence rates. It is shown that especially during the night and particularly in the frequency‐geomagnetic latitude intervals with a low average wave intensity, contribution of lightning‐generated whistlers to the overall wave intensity is significant. At frequencies below 1 kHz, where all six electromagnetic wave components were measured during specific intervals, the study is accompanied by analysis of wave propagation directions. When we limit the analysis only to fractional‐hop whistlers, which propagate away from the Earth, we find a reasonable agreement with results obtained from the whole data set. This also confirms the validity of the whistler occurrence rate analysis at higher frequencies.

Both ray theory and full-wave models of Very Low Frequency transmission through the ionospheric D-layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low-inclination Communication/Navigation Outage Forecast System satellite to test this semi-quantitatively, for broadband Very Low Frequency emissions from lightning. Approximate ground-truthing of the incident wavefields in the Earth Ionosphere Waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes < 26 deg. Thus our conclusions, too, must be limited to the near-equatorial region, and are not necessarily predictive of mid-latitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of Very Low Frequency lightning emissions through the D-layer, at a level exceeding model predictions by at least an order-of-magnitude. We show that kilometric-scale D-layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D-layer transmission for transmission from powerful man-made radio beacons.

Recently, the generation of rising-tone chorus has been implemented with one-dimensional (1-D) particle-in-cell (PIC) simulations in an inhomogeneous background magnetic field, where both the propagation of waves and motion of electrons are simply forced to be parallel to the background magnetic field. In this paper, we have developed a two-dimensional(2-D) general curvilinear PIC simulation code, and successfully reproduced rising-tone chorus waves excited from an anisotropic electron distribution in a 2-D mirror field. Our simulation results show that whistler waves are mainly generated around the magnetic equator, and continuously gain growth during their propagation toward higher-latitude regions. The rising-tone chorus waves are formed off the magnetic equator, which propagate quasi-parallel to the background magnetic field with the wave normal angle smaller than 25°. Due to the propagating effect, the wave normal angle of chorus waves is increasing during their propagation toward higher-latitude regions along an enough curved field line. The chirping rate of chorus waves are found to be larger along a field line with a smaller curvature.

Whistler mode waves play a major role in the energy dynamics of the Earth's magnetosphere. Numerical raytracing has been used for many years to determine the propagation trajectories of whistler mode waves from various sources, both natural and anthropogenic. Previous work has been under the ideal cold plasma assumption even though temperatures of the background ions and electrons are in the range of several eV. We perform numerical raytracing with the inclusion of finite electron and ion temperatures to more accurately model the plasma environment of the Earth's magnetosphere. Finite temperature effects are found to play a significant role in the whistler mode refractive index surface only when the wave frequency is near the lower hybrid resonance frequency and the wave normal angle is oblique. In such cases, the primary effect on whistler mode propagation is to lower the refractive index magnitude and increase the group velocity with slight modifications to the ray trajectories. Landau damping is shown to increase slightly with the inclusion of finite temperature.

We develop a Bayesian spectral analysis technique that calculates the probability distribution functions of a superposition of wave modes each described by a linear growth rate, a frequency, and a chirp rate. The Bayesian framework has a number of advantages, including (1) reducing the parameter space by integrating over the amplitude and phase of the wave, (2) incorporating the data from each channel to determine the model parameters such as frequency which leads to high-resolution results in frequency and time, (3) the ability to consider the superposition of waves where the wave parameters are closely spaced, (4) the ability to directly calculate the expectation value of wave parameters without resorting to ensemble averages, and (5) the ability to calculate error bars on model parameters. We examine one rising-tone chorus element in detail from a disturbed time on 14 November 2012 using burst mode waveform data of the three components of the electric and magnetic field from the EMFISIS instrument on board NASA's Van Allen Probes. The results demonstrate that subelements are likely composed of almost linear waves that are nearly parallel propagating with continuously changing wave parameters such as frequency and wave vector. Between subelements the wave parameters of the dominant mode undergoes a discrete change in frequency and wave vector. Near the boundary of subelements multiple waves are observed such that the evolution of the waves is reminiscent of wave-wave processes such as parametric decay or nonlinear induced scattering by particles. These nonlinear processes may affect the saturation of the whistler mode chorus instability.

We show observations of whistler mode waves in both the low-latitude boundary layer (LLBL) and on closed magnetospheric field lines during a crossing of the dayside reconnecting magnetopause by the ...

Quasi-linear diffusion coefficients are considered for highly oblique whistler mode waves, which exhibit a singular “resonance cone” in cold plasma theory. The refractive index becomes both very large and rapidly varying as a function of wave parameters, making the diffusion coefficients difficult to calculate and to characterize. Since such waves have been repeatedly observed both outside and inside the plasmasphere, this problem has received renewed attention. Here the diffusion equations are analytically treated in the limit of large refractive index μ. It is shown that a common approximation to the refractive index allows the associated “normalization integral” to be evaluated in closed form and that this can be exploited in the numerical evaluation of the exact expression. The overall diffusion coefficient formulas for large μ are then reduced to a very simple form, and the remaining integral and sum over resonances are approximated analytically. These formulas are typically written for a modeled distribution of wave magnetic field intensity, but this may not be appropriate for highly oblique whistlers, which become quasi-electrostatic. Thus, the analysis is also presented in terms of wave electric field intensity. The final results depend strongly on the maximum μ (or μ∥) used to model the wave distribution, so realistic determination of these limiting values becomes paramount.

The solar wind electron temperature anisotropy is regulated by a number of physical processes, which include adiabatic expansion, electron Coulomb collisions, and microinstabilities. In the collisionless limit, the measured electron temperature anisotropy is constrained by the marginal threshold conditions for whistler (electromagnetic electron cyclotron or EMEC) and firehose instabilities, which are excited by excessive perpendicular and parallel temperature anisotropies, respectively. In the literature, these thresholds are expressed as inverse relationships between the electron temperature ratio and parallel beta, which are constructed on the basis of linear stability analysis and empirical fitting. In the present paper, macroscopic quasi-linear kinetic theory of whistler (or EMEC) instability is employed in order to investigate the time development of the instability. One-dimensional particle-in-cell (PIC) simulation is also carried out, and it is found that PIC simulation confirms the validity of the macroscopic quasi-linear approach. It is also found that the saturation stage of the instability naturally corresponds to the threshold condition, thus confirming the inverse relationship. The present finding shows that the macroscopic quasi-linear kinetic theory may be a valid theoretical tool for dynamical description of the solar wind.

We present observations from the Van Allen Probes spacecraft that identify a region of intense whistler mode activity within a large density enhancement outside of the plasmasphere. We speculate that this density enhancement is part of a remnant plasmaspheric plume, with the observed wave being driven by a weakly anisotropic electron injection that drifted into the plume and became nonlinearly unstable to whistler emission. Particle measurements indicate that a significant fraction of thermal (

The environmental impact of power line emission and power line harmonic radiation (PLHR) in near-Earth space has become an increasing concern. In the years 2004–2010, based on the data of microsatellite DEMETER, 133 PLHR events are detected in near-Earth space above China. PLHR has a close correlation with the development of China's electric power network. Its central frequency appears to depend on the latitude. The geographic distribution of the events occurs in clusters. Several events take place continuously above specific regions. PLHR shows no significant dependence on geomagnetic activity. There are more events in daytime than in nighttime and more in winter than in summer. The differences of naturally generated whistlers and power consumption between day and night and the strong thunderstorms in local summer may lead to such diurnal and seasonal differences of PLHR.

The evolution of the whistler anisotropy instability relevant to whistler-mode chorus waves in the Earth's inner magnetosphere is studied using kinetic simulations and is compared with satellite observations. The electron distribution is constrained by the whistler anisotropy instability to a marginal stability state and presents an upper bound of electron anisotropy, which agrees with satellite observations. The electron beta β∥e separates whistler waves into two groups: (i) quasi-parallel whistler waves for β∥e≳0.02 and (ii) oblique whistler waves close to the resonance cone for β∥e≲0.02. Landau damping is important in the saturation and relaxation stage of the oblique whistler wave growth. The saturated magnetic field energy of whistler waves roughly scales with the electron beta β∥e2, shown in both simulations and satellite observations. These results suggest the critical role of electron beta β∥e in determining the whistler wave properties in the inner magnetosphere.

We study the problem of energy exchange between waves and particles, which leads to energization of the latter, in an unstable plasma typical of the radiation belts. The ongoing Van Allen Probes space mission brought this problem among the most discussed in space physics. A free energy which is present in an unstable plasma provides the indispensable condition for energy transfer from lower energy particles to higher energy particles via resonant wave-particle interaction. This process is studied in detail by the example of electron interactions with whistler-mode wave packets originated from lightning induced emission. We emphasize that in an unstable plasma, the energy source for electron energization is the energy of other particles, rather than the wave energy as is often assumed. The way by which the energy is transferred from lower to higher energy particles includes two processes that operate concurrently, in the same space-time domain, or sequentially, in different space-time domains, in which a given wave packet is located. In the first process, one group of resonant particles with an unstable distribution gives the energy to the wave. The second process consists in wave absorption by another group of resonant particles with a stable distribution, whose energy therefore increases. We argue that this mechanism represents an efficient means of electron energization in the radiation belts.

Wave-particle interactions with whistler chorus waves are believed to provide a primary acceleration for electrons in the outer radiation belt. Previous models for flux enhancement of the radiation belt have assumed the stochastic process as a diffusion manner of successive random-phase interactions, but physical mechanisms for the acceleration are not fully incorporated in these models because of the lack of a nonlinear scattering process. Here we report rapid increase in relativistic electron flux by using an innovative computer simulation model that incorporates not only diffusive process but also nonlinear scattering processes. The simulations show that three types of scattering simultaneously occur, which are diffusive, phase-trapping, and phase-bunching. It is found that the phase-trapping is the most efficient mechanism to produce the MeV electrons rapidly in the scattering processes. The electrons are accelerated from 400 keV to over 1 MeV in time scale less than 60 seconds. On the other hand, as the phase-trapping is suppressed by the breaking of relative phase angle between waves and gyrating electrons during the interaction, the increase of electron flux at MeV energy is clearly reduced. Our simulations conclude that the phase-trapping process causes a significant effect for the increase in relativistic electron flux, and suggest that a quasi-linear diffusion model is not always valid to fully describe the relativistic electron acceleration.

Whistler waves are believed to play an important role during magnetic reconnection. Here we report the near-simultaneous occurrence of two types of the whistler-mode waves in the magnetotail Hall r ...

Proton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here, we use particle-in-cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron free energy, so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability., Comment: 11 pages, 19 figures

Puzzling satellite observations of butterfly pitch angle distributions and rapid dropouts of 30–150 keV electrons are widespread in the Earth's radiation belts. Several mechanisms have been proposed to explain these observations, such as enhanced outward radial diffusion combined with magnetopause shadowing or scattering by intense magnetosonic waves, but their effectiveness is mainly limited to storm times. Moreover, the scattering of 30–150 keV electrons via cyclotron resonance with intense parallel chorus waves should be limited to particles with equatorial pitch angle smaller than 70°–75°, leaving unaffected a large portion of the population. In this paper, we investigate the possible effects of oblique whistler mode waves, noting, in particular, that Landau resonance with very oblique waves can occur up to ∼89°. We demonstrate that such very oblique chorus waves with realistic amplitudes can very efficiently nonlinearly transport nearly equatorially mirroring electrons toward smaller pitch angles where nonlinear scattering (phase bunching) via cyclotron resonance with quasi-parallel waves can take over and quickly send them to much lower pitch angles

We present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 21 September 2012 to 1 August 2014. We show that statistically, the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (f(sub cP)) has a distinct funnel-shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extra-ordinary (whistler) mode at wave normal angles (theta(sub k)) near 90 deg. Performing polarization analysis on synthetic waveforms composed from a superposition of extra-ordinary mode plane waves with theta(sub k) randomly chosen between 87 and 90 deg, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to theta(sub k) of 60 deg, suggesting that another approach is necessary to estimate the true distribution of theta(sub k). We find that the histograms of the synthetically derived ellipticities and theta(sub k) are consistent with the observations of ellipticities and theta(sub k) derived using polarization analysis.We make estimates of the median equatorial theta(sub k) by comparing observed and model ray tracing frequency-dependent probability occurrence with latitude and give preliminary frequency dependent estimates of the equatorial theta(sub k) distribution around noon and 4 R(sub E), with the median of approximately 4 to 7 deg from 90 deg at f/f(sub cP) = 2 and dropping to approximately 0.5 deg from 90 deg at f/f(sub cP) = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies.

Lightning-generated whistler waves are electromagnetic plasma waves in the very low frequency (VLF) band, which play an important role in the dynamics of radiation belt particles. In this paper, we statistically analyze simultaneous waveform data from the Van Allen Probes (Radiation Belt Storm Probes, RBSP) and global lightning data from the World Wide Lightning Location Network (WWLLN). Data were obtained between July to September 2013 and between March and April 2014. For each day during these periods, we predicted the most probable 10 min for which each of the two RBSP satellites would be magnetically conjugate to lightning producing regions. The prediction method uses integrated WWLLN stroke data for that day obtained during the three previous years. Using these predicted times for magnetic conjugacy to lightning activity regions, we recorded high time resolution, burst mode waveform data. Here we show that whistlers are observed by the satellites in more than 80% of downloaded waveform data. About 22.9% of the whistlers observed by RBSP are one-to-one coincident with source lightning strokes detected by WWLLN. About 40.1% more of whistlers are found to be one-to-one coincident with lightning if source regions are extended out 2000 km from the satellites footpoints. Lightning strokes with far-field radiated VLF energy larger than about 100 J are able to generate a detectable whistler wave in the inner magnetosphere. One-to-one coincidences between whistlers observed by RBSP and lightning strokes detected by WWLLN are clearly shown in the L shell range of L = 1–3. Nose whistlers observed in July 2014 show that it may be possible to extend this coincidence to the region of L≥4.

At Earth's dayside magnetopause asymmetric magnetic reconnection occurs between the cold dense magnetosheath plasma and the hot tenuous magnetospheric plasma, which differs significantly from symme ...

Interplanetary shocks in the heliosphere modify the solar wind through which they pass. In particular, shocks play an important role in particle acceleration. During the extended solar minimum (2007–2010) STEREO observed 65 forward shocks driven by stream interactions (SI), with magnetosonic Mach numbers Mms ≈ 1.1–4.0 and shock normal angles θBN ~ 20–87°. We analyze the waves associated with these shocks and find that the region upstream can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) waves (f ~ 10−2–10−1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is most probably associated with local kinetic ion instabilities. We find that when the Mach number (Mms) is low and the shock is quasi-perpendicular ( θBN > 45°) whistler waves remain close to the shock. As Mms increases, the shock profile changes and can develop a foot and overshoot associated with ion reflection and gyration. Whistler precursors can be superposed on the foot region, so that some quasi-perpendicular shocks have characteristics of both subcritical and supercritical shocks. When the shock is quasi-parallel ( θBN

We present observations of the radiation belts from the Helium Oxygen Proton Electron and Magnetic Electron Ion Spectrometer particle detectors on the Van Allen Probes satellites that illustrate the energy dependence and L shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on 1 March in more detail. The observations show the following: (a) at all L shells, lower energy electrons are enhanced more often than higher energies; (b) events that fill the slot region are more common at lower energies; (c) enhancements of electrons in the inner zone are more common at lower energies; and (d) even when events do not fully fill the slot region, enhancements at lower energies tend to extend to lower L shells than higher energies. During enhancement events the outer zone extends to lower L shells at lower energies while being confined to higher L shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L shells for lower energies. Both boundaries are nearly straight in log(energy) versus L shell space. At energies below a few 100 keV, radiation belt electron penetration through the slot region into the inner zone is commonplace, but the number and frequency of “slot filling” events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy‐ and L shell‐dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions., Key Points Radiation belt dynamics are a strong function of energy and L shellEvents that fill the slot region are common at lower energies and rare at higher energiesDuring enhancement events different energies are enhanced in different spatial regions

In a recent paper, Ahmadi et al. (2016) analyze the effect of electron temperature anisotropy on proton mirror instability. They find that the electron whistler instability grows faster and consumes all the available electron free energy so that no anisotropy is left to fuel the proton mirror mode growth. In this comment we present both observational and theoretical arguments about why we think this is incorrect.