First observation of fluid-like eddy-dominant bursty bulk flow turbulence in the Earth's tail plasma sheet

Turbulence is a ubiquitous phenomenon in neutral and conductive fluids. According to classical theory, turbulence is a rotating flow containing vortices of different scales. Eddies play a fundamental role in the nonlinear cascade of kinetic energy at different scales in turbulent flow. In conductive fluids, the Alfvénic/kinetic Alfvénic wave (AW/KAW) is the new "cell" of magnetohydrodynamic (MHD) turbulence (frozen-in condition). Wave energy, which has equal kinetic and magnetic energy, is redistributed among multiple-scale Fourier modes and transferred from the large MHD scale to the small kinetic scale through the collision of counter-propagating Alfvénic wave packages propagating along the magnetic field line. Fluid-like eddy-dominant plasma flow turbulence has never been found in space since the launch of the first satellite in 1957. In this paper, we report the first observation of eddy-dominant turbulence within magnetic reconnection-generated fast flow in the Earth's tail plasma sheet by the Magnetospheric Multiscale Spacecraft (MMS). In eddy-dominant turbulent reconnection jet, ions dominate the flow field while electrons dominate current and magnetic fluctuations. Our findings shed new light on the nonlinear kinetic and magnetic energy cascade in MHD turbulence.

Turbulent current sheet frozen in bursty bulk flow: observation and model

Utilizing four-point joint observations by Magnetospheric Multiscale Spacecraft (MMS), we investigate the main features of the current sheet frozen in (CSFI) the bursty bulk flow. Typical event on the steady long-lasting BBF on July 23, 2017 shows the enhanced dawn-dusk current (Jy₀) in the CSFI (β ~ 10). The magnitude of the Jy₀ in the CSFI is about 5.5 nA/m². The CSFI is highly turbulent, with the ratio of ∆J/J₀ of ~ 2 (where ∆J is perturbed J). The turbulent CSFI is characterized by intermittent current coherent structures. The magnitude of the spiky-J at coherent structures is typically above 30 nA/m². Spectrum analysis exhibits that BBF turbulence follows distinct dissipation laws inside and outside the CSFI. Based on MMS observations, we propose a new model of the BBF in the framework of magnetohydrodynamics. In this model, the BBF is depicted as a closed plasma system with the localized current sheet frozen at the center of the flow (Taylor’s hypothesis). In the light of principle of Helmholtz-decomposition, the BBF motion in the tail plasma sheet is explained. The model also predicts the thermal expansion of the BBF after leaving the reconnection source region.

Automated Detection Algorithm for Mesoscale Heated Regions in TWINS Ion Temperature Maps

Earth's magnetotail plays a critical role in the dynamics of the magnetosphere, particularly during intervals of geomagnetic activity. To improve our understanding of the ion dynamics in this region, energetic neutral atom (ENA) imaging can provide global measurements to place in situ measurements in context and validate simulations. The NASA Two Wide-angle Imaging Neutral-atom Spectrometers mission provided near-continuous observations using ENA imagers. ENA data can be used to calculate maps of equatorial ion temperatures that often show observations of regions of enhanced temperatures associated with phenomena in the magnetotail such as magnetic reconnection and narrow flow channels. We present an algorithm that can be used to search through a collection of these maps to identify intervals with such enhancements for further study. The algorithm results are validated against two sets of related phenomena: (a) a database of dipolarizing flux bundle (DFB) measurements from THEMIS and (b) a list of substorm onsets from SuperMAG. We demonstrate that the algorithm is very good at identifying intervals when there are DFB measurements or substorm onsets as long as there sufficient ENA data. We discuss some potential scientific studies that can result from use of the algorithm. We also show a preliminary application of the algorithm to simulation output to demonstrate the usefulness for other datasets, facilitate comparative studies, and introduce a new method for model validation.

Characteristics of Plasma Dynamics in Current Sheets Formed in Helium Plasma

The characteristic features of plasma acceleration in the current sheets are discussed on the basis of an analysis of the structure of electrodynamic forces at successive stages of the evolution of the current sheets formed in the plasma with helium ions. Of particular interest is the generation of reverse currents at the side edges of the sheet and the appearance of forces, which are braking previously accelerated plasma flows.

Electrostatic Solitary Structures in Space Plasmas: Soliton Perspective

Occurrence of electrostatic solitary waves (ESWs) is ubiquitous in space plasmas, e.g., solar wind, Lunar wake and the planetary magnetospheres. Several theoretical models have been proposed to interpret the observed characteristics of the ESWs. These models can broadly be put into two main categories, namely, Bernstein–Green–Kruskal (BGK) modes/phase space holes models, and ion- and electron- acoustic solitons models. There has been a tendency in the space community to favor the models based on BGK modes/phase space holes. Only recently, the potential of soliton models to explain the characteristics of ESWs is being realized. The idea of this review is to present current understanding of the ion- and electron-acoustic solitons and double layers models in multi-component space plasmas. In these models, all the plasma species are considered fluids except the energetic electron component, which is governed by either a kappa distribution or a Maxwellian distribution. Further, these models consider the nonlinear electrostatic waves propagating parallel to the ambient magnetic field. The relationship between the space observations of ESWs and theoretical models is highlighted. Some specific applications of ion- and electron-acoustic solitons/double layers will be discussed by comparing the theoretical predictions with the observations of ESWs in space plasmas. It is shown that the ion- and electron-acoustic solitons/double layers models provide a plausible interpretation for the ESWs observed in space plasmas.

Network community structure of substorms using SuperMAG magnetometers

Geomagnetic substorms are a global magnetospheric reconfiguration, during which energy is abruptly transported to the ionosphere. Central to this are the auroral electrojets, large-scale ionospheric currents that are part of a larger three-dimensional system, the substorm current wedge. Many, often conflicting, magnetospheric reconfiguration scenarios have been proposed to describe the substorm current wedge evolution and structure. SuperMAG is a worldwide collaboration providing easy access to ground based magnetometer data. Here we show application of techniques from network science to analyze data from 137 SuperMAG ground-based magnetometers. We calculate a time-varying directed network and perform community detection on the network, identifying locally dense groups of connections. Analysis of 41 substorms exhibit robust structural change from many small, uncorrelated current systems before substorm onset, to a large spatially-extended coherent system, approximately 10 minutes after onset. We interpret this as strong indication that the auroral electrojet system during substorm expansions is inherently a large-scale phenomenon and is not solely due to many meso-scale wedgelets.

Mesoscale Structures in Earth's Magnetotail Observed Using Energetic Neutral Atom Imaging

Mesoscale structures in Earth's magnetotail are a primary feature of particle transport to the inner magnetosphere during storms and substorms. We demonstrate that such structures can be observed in energetic neutral atom (ENA) data which can provide remote, global images of the magnetosphere. In particular, we present localized regions of increased ion temperatures that appear in equatorial ion temperature maps calculated from Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) ENA data. These regions are associated with a dipolarization front with bursty ion flows measured by Magnetospheric MultiScale (MMS) and are concurrent with substorm features observed in field aligned currents (FAC) from Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements. We conduct a magnetohydrodynamics simulation of the same event and show simulated ion temperatures, ion flows, and FACs that agree with the measurements. However, the observed plasma heating is less intense in the simulated results than in the TWINS and MMS data, indicating that some heating processes may be missing from the model.

Behavior of compressed plasmas in magnetic fields

Plasma in the earth’s magnetosphere is subjected to compression during geomagnetically active periods and relaxation in subsequent quiet times. Repeated compression and relaxation is the origin of much of the plasma dynamics and intermittency in the near-earth environment. An observable manifestation of compression is the thinning of the plasma sheet resulting in magnetic reconnection when the solar wind mass, energy, and momentum floods into the magnetosphere culminating in the spectacular auroral display. This phenomenon is rich in physics at all scale sizes, which are causally interconnected. This poses a formidable challenge in accurately modeling the physics. The large-scale processes are fluid-like and are reasonably well captured in the global magnetohydrodynamic (MHD) models, but those in the smaller scales responsible for dissipation and relaxation that feed back to the larger scale dynamics are often in the kinetic regime. The self-consistent generation of the small-scale processes and their feedback to the global plasma dynamics remains to be fully explored. Plasma compression can lead to the generation of electromagnetic fields that distort the particle orbits and introduce new features beyond the purview of the MHD framework, such as ambipolar electric fields, unequal plasma drifts and currents among species, strong spatial and velocity gradients in gyroscale layers separating plasmas of different characteristics, etc. These boundary layers are regions of intense activity characterized by emissions that are measurable. We study the behavior of such compressed plasmas and discuss the relaxation mechanisms to understand their measurable signatures as well as their feedback to influence the global scale plasma evolution.

Contribution of Bursty Bulk Flows to the Global Dipolarization of the Magnetotail During an Isolated Substorm

This paper addresses the question of the contribution of azimuthally localized flow channels and magnetic field dipolarizations embedded in them in the global dipolarization of the inner magnetosphere during substorms. We employ the high-resolution Lyon-Fedder-Mobarry global magnetosphere magnetohydrodynamic model and simulate an isolated substorm event, which was observed by the geostationary satellites and by the Magnetospheric Multiscale spacecraft. The results of our simulations reveal that plasma sheet flow channels (bursty bulk flows, BBFs) and elementary dipolarizations (dipolarization fronts, DFs) occur in the growth phase of the substorm but are rare and do not penetrate to the geosynchronous orbit. The substorm onset is characterized by an abrupt increase in the occurrence and intensity of BBFs/DFs, which penetrate well earthward of the geosynchronous orbit during the expansion phase. These azimuthally localized structures are solely responsible for the global (in terms of the magnetic local time) dipolarization of the inner magnetosphere toward the end of the substorm expansion. Comparison with the geostationary satellites and Magnetospheric Multiscale data shows that the properties of the BBFs/DFs in the simulation are similar to those observed, which gives credence to the above results. Additionally, the simulation reveals many previously observed signatures of BBFs and DFs, including overshoots and oscillations around their equilibrium position, strong rebounds and vortical tailward flows, and the corresponding plasma sheet expansion and thinning.

Explosive Magnetotail Activity

Modes and manifestations of the explosive activity in the Earth's magnetotail, as well as its onset mechanisms and key pre-onset conditions are reviewed. Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection. Reconnection onset may require stretching and thinning of the sheet down to electron scales. It may also start in thicker sheets in regions with a tailward gradient of the equatorial magnetic field B z ; in this case it begins as an ideal-MHD instability followed by the generation of bursty bulk flows and dipolarization fronts. Indeed, remote sensing and global MHD modeling show the formation of tail regions with increased B z , prone to magnetic reconnection, ballooning/interchange and flapping instabilities. While interchange instability may also develop in such thicker sheets, it may grow more slowly compared to tearing and cause secondary reconnection locally in the dawn-dusk direction. Post-onset transients include bursty flows and dipolarization fronts, micro-instabilities of lower-hybrid-drift and whistler waves, as well as damped global flux tube oscillations in the near-Earth region. They convert the stretched tail magnetic field energy into bulk plasma acceleration and collisionless heating, excitation of a broad spectrum of plasma waves, and collisional dissipation in the ionosphere. Collisionless heating involves ion reflection from fronts, Fermi, betatron as well as other, non-adiabatic, mechanisms. Ionospheric manifestations of some of these magnetotail phenomena are discussed. Explosive plasma phenomena observed in the laboratory, the solar corona and solar wind are also discussed.

Transport and Loss of Ring Current Electrons Inside Geosynchronous Orbit During the 17 March 2013 Storm

Ring current electrons (1-100 keV) have received significant attention in recent decades, but many questions regarding their major transport and loss mechanisms remain open. In this study, we use the four-dimensional Versatile Electron Radiation Belt code to model the enhancement of phase space density that occurred during the 17 March 2013 storm. Our model includes global convection, radial diffusion, and scattering into the Earth's atmosphere driven by whistler-mode hiss and chorus waves. We study the sensitivity of the model to the boundary conditions, global electric field, the electric field associated with subauroral polarization streams, electron loss rates, and radial diffusion coefficients. The results of the code are almost insensitive to the model parameters above 4.5 R E R E, which indicates that the general dynamics of the electrons between 4.5 R E and the geostationary orbit can be explained by global convection. We found that the major discrepancies between the model and data can stem from the inaccurate electric field model and uncertainties in lifetimes. We show that additional mechanisms that are responsible for radial transport are required to explain the dynamics of ≥40-keV electrons, and the inclusion of the radial diffusion rates that are typically assumed in radiation belt studies leads to a better agreement with the data. The overall effect of subauroral polarization streams on the electron phase space density profiles seems to be smaller than the uncertainties in other input parameters. This study is an initial step toward understanding the dynamics of these particles inside the geostationary orbit.

Kinetic Equilibrium of Dipolarization Fronts

The unprecedented high-resolution data from the Magnetospheric Multi-Scale (MMS) satellites is revealing the physics of dipolarization fronts created in the aftermath of magnetic reconnection in extraordinary detail. The data shows that the fronts contain structures on small spatial scales beyond the scope of fluid framework. A new kinetic analysis, applied to MMS data here, predicts that global plasma compression produces a unique particle distribution in a narrow boundary layer with separation of electron and ion scale physics. Layer widths on the order of an ion gyro-diameter lead to an ambipolar potential across the magnetic field resulting in strongly sheared flows. Gradients along the magnetic field lines create a potential difference, which can accelerate ions and electrons into beams. These small-scale kinetic effects determine the plasma dynamics in dipolarization fronts, including the origin of the distinctive broadband emissions.

A diagnosis of the plasma waves responsible for the explosive energy release of substorm onset

During geomagnetic substorms, stored magnetic and plasma thermal energies are explosively converted into plasma kinetic energy. This rapid reconfiguration of Earth's nightside magnetosphere is manifest in the ionosphere as an auroral display that fills the sky. Progress in understanding of how substorms are initiated is hindered by a lack of quantitative analysis of the single consistent feature of onset; the rapid brightening and structuring of the most equatorward arc in the ionosphere. Here, we exploit state-of-the-art auroral measurements to construct an observational dispersion relation of waves during substorm onset. Further, we use kinetic theory of high-beta plasma to demonstrate that the shear Alfven wave dispersion relation bears remarkable similarity to the auroral dispersion relation. In contrast to prevailing theories of substorm initiation, we demonstrate that auroral beads seen during the majority of substorm onsets are likely the signature of kinetic Alfven waves driven unstable in the high-beta magnetotail.

Energetic Ion Injections Inside Geosynchronous Orbit: Convection- and Drift-Dominated, Charge-Dependent Adiabatic Energization (W = qEd)

Particle injection, a major mode of plasma transport and energization throughout the magnetosphere, has been studied for decades. Nonetheless, the physical processes that lead to the acceleration and transport of very energetic ions in the inner magnetosphere during injection events are still under debate. In this paper, we analyze several injection events occurring near the Van Allen Probes apogee. Our analysis shows that the highest energy of an injected ion population depends on the charge state of that population. We show that most of the helium injected is doubly ionized (He++), while oxygen charge states are consistent with the presence of both ionospheric (O+) and solar wind (O6+) source populations. Based on the findings of our data analysis and with the use of a simple model, we demonstrate that the behavior of each injection of energetic ions near the Van Allen Probes apogee (5 < L < 7 R E) is well explained by simple adiabatic or nearly adiabatic transport within flow channels from higher L (≥10 R E) with velocities at 10 R E ranging between ~200 and 2,000 km/s and falling with inward transport consistent with fixed potential drops across the flow channels. Gradient/curvature drift during transport limits the highest energy/charge observed for each injection at the Van Allen Probes. Even at the highest measured ion energies where gyroradius and scattering effects might be expected to appear, energization depends on charge state but not on ion mass.

Magnetotail Fast Flow Occurrence Rate and Dawn-Dusk Asymmetry at XGSM ∼ -60 RE

As a direct result of magnetic reconnection, plasma sheet fast flows act as primary transporter of mass, flux, and energy in the Earth's magnetotail. During the last decades, these flows were mainly studied within X_GSM>-60R_E , as observations near or beyond lunar orbit were limited. By using 5 years (2011-2015) of ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moons Interaction with the Sun) data, we statistically investigate earthward and tailward flows at around 60 R_E downtail. A significant fraction of fast flows is directed earthward, comprising 43% (v_x >400 km/s) to 56% (v_x >100 km/s) of all observed flows. This suggests that near-Earth and midtail reconnection are equally probable of occurring on either side of the ARTEMIS downtail distance. For fast convective flows (v_⊥x >400 km/s), this fraction of earthward flows is reduced to about 29%, which is in line with reconnection as source of these flows and a downtail decreasing Alfvén velocity. More than 60% of tailward convective flows occur in the dusk sector (as opposed to the dawn sector), while earthward convective flows are nearly symmetrically distributed between the two sectors for low AL (>-400 nT) and asymmetrically distributed toward the dusk sector for high AL (<-400 nT). This indicates that the dawn-dusk asymmetry is more pronounced closer to Earth and moves farther downtail during high geomagnetic activity. This is consistent with similar observations pointing to the asymmetric nature of tail reconnection as the origin of the dawn-dusk asymmetry of flows and other related observables. We infer that near-Earth reconnection is preferentially located at dusk, whereas midtail reconnection (X >- 60R_E ) is likely symmetric across the tail during weak substorms and asymmetric toward the dusk sector for strong substorms, as the dawn-dusk asymmetric nature of reconnection onset in the near-Earth region progresses downtail.

Large-scale energy budget of impulsive magnetic reconnection: Theory and simulation

We evaluate the large-scale energy budget of magnetic reconnection utilizing an analytical time-dependent impulsive reconnection model and a numerical 2-D MHD simulation. With the generalization to compressible plasma, we can investigate changes in the thermal, kinetic, and magnetic energies. We study these changes in three different regions: (a) the region defined by the outflowing plasma (outflow region, OR), (b) the region of compressed magnetic fields above/below the OR (traveling compression region, TCR), and (c) the region trailing the OR and TCR (wake). For incompressible plasma, we find that the decrease inside the OR is compensated by the increase in kinetic energy. However, for the general compressible case, the decrease in magnetic energy inside the OR is not sufficient to explain the increase in thermal and kinetic energy. Hence, energy from other regions needs to be considered. We find that the decrease in thermal and magnetic energy in the wake, together with the decrease in magnetic energy inside the OR, is sufficient to feed the increase in kinetic and thermal energies in the OR and the increase in magnetic and thermal energies inside the TCR. That way, the energy budget is balanced, but consequently, not all magnetic energy is converted into kinetic and thermal energies of the OR. Instead, a certain fraction gets transfered into the TCR. As an upper limit of the efficiency of reconnection (magnetic energy → kinetic energy) we find η_eff=1/2. A numerical simulation is used to include a finite thickness of the current sheet, which shows the importance of the pressure gradient inside the OR for the conversion of kinetic energy into thermal energy.

A comparative study of dipolarization fronts at MMS and Cluster

We present a statistical study of dipolarization fronts (DFs), using magnetic field data from MMS and Cluster, at radial distances below 12 R_E and 20 R_E , respectively. Assuming that the DFs have a semicircular cross section and are propelled by the magnetic tension force, we used multispacecraft observations to determine the DF velocities. About three quarters of the DFs propagate earthward and about one quarter tailward. Generally, MMS is in a more dipolar magnetic field region and observes larger-amplitude DFs than Cluster. The major findings obtained in this study are as follows: (1) At MMS ∼57 % of the DFs move faster than 150 km/s, while at Cluster only ∼35 %, indicating a variable flux transport rate inside the flow-braking region. (2) Larger DF velocities correspond to higher B_z  values directly ahead of the DFs. We interpret this as a snow plow-like phenomenon, resulting from a higher magnetic flux pileup ahead of DFs with higher velocities.

Near-Earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeVelectron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L ∼ 5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ∼40 s and a dispersionless injection of electrons up to ∼3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons.

Two states of magnetotail dipolarization fronts: A statistical study

We study the ion density and temperature in the predipolarization and postdipolarization plasma sheets in the Earth's magnetotail using 9 years (2001-2009) of Cluster data. For our study we selected cases when Cluster observed dipolarization fronts (DFs) with an earthward plasma flow greater than 150km/s. We perform a statistical study of the temperature and density variations during the DF crossings. Earlier studies concluded that on average, the temperature increases while the density decreases across the DF. Our statistical results show a more diverse picture: While ∼54% of the DFs follow this pattern (category A), for ∼28% the temperature decreases while the density increases across the DF (category B). We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of category B showed no clear pattern in the pressure change. Both categories are associated with earthward plasma flows but with some difference: (1) category A flows are faster than category B flows, (2) the observations indicate that category B flows are directed perpendicular to the current in the near-Earth current sheet while category A flows are tilted slightly duskward from this direction, and (3) the background Bz of category B is higher than that of category A. Based on these results, we hypothesize that after reconnection takes place, a bursty bulk flow emerges with category A characteristics, and as it travels earthward, it further evolves into category B characteristics, which is in a more dipolarized region with slower plasma flow (closer to the flow-braking region).

Rapid acceleration of protons upstream of earthward propagating dipolarization fronts

[1] Transport and acceleration of ions in the magnetotail largely occurs in the form of discrete impulsive events associated with a steep increase of the tail magnetic field normal to the neutral plane (Bz ), which are referred to as dipolarization fronts. The goal of this paper is to investigate how protons initially located upstream of earthward moving fronts are accelerated at their encounter. According to our analytical analysis and simplified two-dimensional test-particle simulations of equatorially mirroring particles, there are two regimes of proton acceleration: trapping and quasi-trapping, which are realized depending on whether the front is preceded by a negative depletion in Bz . We then use three-dimensional test-particle simulations to investigate how these acceleration processes operate in a realistic magnetotail geometry. For this purpose we construct an analytical model of the front which is superimposed onto the ambient field of the magnetotail. According to our numerical simulations, both trapping and quasi-trapping can produce rapid acceleration of protons by more than an order of magnitude. In the case of trapping, the acceleration levels depend on the amount of time particles stay in phase with the front which is controlled by the magnetic field curvature ahead of the front and the front width. Quasi-trapping does not cause particle scattering out of the equatorial plane. Energization levels in this case are limited by the number of encounters particles have with the front before they get magnetized behind it.

Plasma jet braking: energy dissipation and nonadiabatic electrons

We report in situ observations by the Cluster spacecraft of wave-particle interactions in a magnetic flux pileup region created by a magnetic reconnection outflow jet in Earth's magnetotail. Two distinct regions of wave activity are identified: lower-hybrid drift waves at the front edge and whistler-mode waves inside the pileup region. The whistler-mode waves are locally generated by the electron temperature anisotropy, and provide evidence for ongoing betatron energization caused by magnetic flux pileup. The whistler-mode waves cause fast pitch-angle scattering of electrons and isotropization of the electron distribution, thus making the flow braking process nonadiabatic. The waves strongly affect the electron dynamics and thus play an important role in the energy conversion chain during plasma jet braking.

Solitary electromagnetic pulses detected with super-Alfvénic flows in Earth's geomagnetic tail

Solitary nonlinear (deltaB/B>>1) electromagnetic pulses have been detected in Earth's geomagnetic tail accompanying plasmas flowing at super-Alfvénic speeds. The pulses in the current sheet had durations of approximately 5 s, were left-hand circularly polarized, and had phase speeds of approximately the Alfvén speed in the plasma frame. These pulses were associated with a field-aligned current J(parallel) and observed in low density (approximately 0.3 cm(-3)), high temperature (T(e) approximately T(i) approximately 3x10(7) K), and beta approximately 10 plasma that included electron and ion beams streaming along B. The wave activity was enhanced from below the ion cyclotron frequency to electron cyclotron and upper hybrid frequencies. The detailed properties suggest the pulses are nonlinearly steepened ion cyclotron or Alfvén waves.