We evaluate the location, extent, and energy range of electron precipitation driven by ElectroMagnetic Ion Cyclotron (EMIC) waves using coordinated multisatellite observations from near‐equatorial and Low‐Earth‐Orbit (LEO) missions. Electron precipitation was analyzed using the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD‐II) CubeSats, in conjunction either with typical EMIC‐driven precipitation signatures observed by Polar Orbiting Environmental Satellites (POES) or with in situ EMIC wave observations from Van Allen Probes. The multievent analysis shows that electron precipitation occurred in a broad region near dusk (16–23 MLT), mostly confined to 3.5–7.5 L‐shells. Each precipitation event occurred on localized radial scales, on average ∼0.3 L. Most importantly, FIREBIRD‐II recorded electron precipitation from ∼200 to 300 keV to the expected ∼MeV energies for most cases, suggesting that EMIC waves can efficiently scatter a wide energy range of electrons.

This study investigates the energy spectrum of electron microbursts observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics II (FIREBIRD‐II, henceforth FIREBIRD) CubeSats. FIREBIRD is a pair of CubeSats, launched in January 2015 into a low Earth orbit, which focuses on studying electron microbursts. High‐resolution electron data from FIREBIRD‐II consist of 5 differential energy channels between 200 keV and 1 MeV and a 1 MeV integral channel. This covers an energy range that has not been well studied from low Earth orbit with good energy and time resolution. This study aims to improve the understanding of the scattering mechanism behind electron microbursts by investigating their spectral properties and their relationship with the equatorial electron population under different geomagnetic conditions. Microbursts are identified in the region of the North Atlantic where FIREBIRD only observes electrons in the bounce loss cone. The electron flux and exponential energy spectrum of each microburst are calculated using a FIREBIRD instrument response modeled in GEANT4 (GEometry ANd Tracking) and compared with the near‐equatorial electron spectra measured by the Van Allen Probes. Microbursts occurring when the Auroral Electrojet (AE) index is enhanced tend to carry more electrons with relatively higher energies. The microburst scattering mechanism is more efficient at scattering electrons with lower energies; however, the difference in scattering efficiency between low and high energy is reduced during periods of enhanced AE.

We present observations that provide the strongest evidence yet that discrete whistler mode chorus packets cause relativistic electron microbursts. On 20 January 2016 near 1944 UT the low Earth orbiting CubeSat Focused Investigations of Relativistic Electron Bursts: Intensity, Range, and Dynamics (FIREBIRD II) observed energetic microbursts (near L = 5.6 and MLT = 10.5) from its lower limit of 220 keV, to 1 MeV. In the outer radiation belt and magnetically conjugate, Van Allen Probe A observed rising‐tone, lower band chorus waves with durations and cadences similar to the microbursts. No other waves were observed. This is the first time that chorus and microbursts have been simultaneously observed with a separation smaller than a chorus packet. A majority of the microbursts do not have the energy dispersion expected for trapped electrons bouncing between mirror points. This confirms that the electrons are rapidly (nonlinearly) scattered into the loss cone by a coherent interaction with the large amplitude (up to ∼900 pT) chorus. Comparison of observed time‐averaged microburst flux and estimated total electron drift shell content at L = 5.6 indicate that microbursts may represent a significant source of energetic electron loss in the outer radiation belt.

We propose a mission called SADE, the Starspot And Dynamo Explorer, to study dynamo activity in nearby late-type stars. The onboard instruments will be a Ca-K telescope for magnetically dominated chromospheric emission, and an X-ray grazing incidence telescope to study coronal emission. We design the mission for a life-time of 15 years or longer to capture a full activity cycle for most solar-type stars. We aim to firmly establish the spectrum of the relation between chromospheric and corona' emission in late-type stars, and capture one or more stars going into or coming out of a Maunder type minimum. Operation costs will be kept to a minimum by automating mission operations to a maximum, and have the science operations be carried out by students at Montana State University.

[1] A series of nearly simultaneous cusp crossings by the Polar and Fast Auroral Snapshot (FAST) spacecraft are used to investigate the development of cusp structures such as sudden changes in the energy of cusp precipitating ions. While such changes are generally interpreted as temporal signatures, recent investigations show evidence that such features can also be interpreted as spatial structures. Our analysis of four events during stable solar wind conditions confirms that cusp structures observed by one satellite are remarkably similar to cusp features observed up to several hours later by a second satellite. Using the spatial separation of the Polar and FAST spacecraft, the cusp features could also be traced over several hours in magnetic local time. These similarities led to the conclusion that large- scale cusp structures are spatial structures related to global ionospheric convection pattern set up by magnetic merging and not the result of temporal variations in reconnection parameters.

Ion beams flowing downward, into the ionosphere, along the Earth's magnetic field have frequently been observed by the FAST satellite in the auroral zone. These discrete downward moving ion beams (DFI) have been characterized by Klumpar et al. [1999] who interpreted the horseshoe‐shaped distributions as being consistent with acceleration in a parallel potential drop above the satellite, followed by motion into a region of increased magnetic field strength. The down‐flowing ion beams are associated with an intense narrowband electrostatic emission at the lower hybrid frequency, polarized perpendicular to the geomagnetic field. Hydrogen cyclotron harmonics both above and below the lower hybrid frequency are also very common. These are the first observations of down‐flowing ions and associated waves outside of the cusp, and the physical mechanism producing the ions is very different from the one associated with cusp ion injections. The DFI events that had a monotonic increase in energy were associated with a clear field‐aligned current signature. The DFI densities were usually ∼5–10/cc, whereas the background plasma had densities up to 100/cc. The wave and DFI observations are consistent with linear dispersion relation calculations and simulations with ion ring distributions that show that the instability is due to coupling of the ion Bernstein waves to the lower hybrid wave. In addition, for a few events, electrostatic ion cyclotron waves were observed. Such waves are usually associated with up‐going ion beams and have not previously been seen with DFI, which have a very different shape in the distribution.

FAST satellite observations of spatially localized regions of electron and ion precipitation with concomitant paired upward and downward field‐aligned currents and duskward electric field enhancements at high (> 80° invariant latitude) magnetic latitudes are presented. Each pass of several across the polar cap was made during a period of persistent northward interplanetary magnetic field, and was characterized by the presence of several of these precipitation regions. In each case, the precipitation regions were associated with jets of enhanced antisunward convection, with electron precipitation restricted to the upward current region, and no energetic electron outflow in the downward current region, and ion precipitation spread over broader regions, possibly by time‐of‐flight effects. We compare these low‐altitude features to those expected for source regions lying in a reconnection site at the lobe magnetopause, a bursty bulk flow in the plasma sheet, and a surface wave on the low‐latitude boundary layer (LLBL). We find that the lobe reconnection model successfully describes the observed electrodynamics of the arcs, as well as the electron and ion source temperatures, but can not readily explain the presence of precipitating O+ and He+ in addition to H+ and He++. The plasma sheet source model can explain the composition of the ion precipitation but predicts higher electron and ion source temperatures than are observed, may require the coincidence of bursty bulk flows with extensions of the plasma sheet into the lobe, and may not be consistant with other observations of auroral phenomenology. The LLBL surface wave model does not readily explain the observed electrodynamics of the arcs and is not consistent with the observed offsets between electron and ion precipitation.

FAST particle and wave data for a single nightside auroral zone crossing are utilized to examine the free energy source for electrostatic ion cyclotron (EIC) waves. Comparisons of the unstable wave modes, obtained by an electrostatic linear dispersion relation solver, to the observed waves for two intervals with upflowing ion beams and two with upflowing electron beams are consistent with the conclusion that the observed waves near the cyclotron frequencies are EIC which are driven by the electron drift both in the upgoing ion beam regions and in the upgoing electron regions. A limitation is that the drifting bi‐Maxwellian model used in the dispersion relation is not a good match to the observed upflowing electron distributions. The observed ion beams do not drive EIC waves; however, the relative drift of the various ion species comprising the ion beam can drive low frequency (<∼50 Hz) waves unstable. The electron drift, during some intervals, also destabilizes electron acoustic waves.

We report observations of “fast solitary waves” that are ubiquitous in downward current regions of the mid‐altitude auroral zone. The single‐period structures have large amplitudes (up to 2.5 V/m), travel much faster than the ion acoustic speed, carry substantial potentials (up to ∼100 Volts), and are associated with strong modulations of energetic electron fluxes. The amplitude and speed of the structures distinguishes them from ion‐acoustic solitary waves or weak double layers. The electromagnetic signature appears to be that of an positive charge (electron hole) traveling anti‐earthward. We present evidence that the structures are in or near regions of magnetic‐field‐aligned electric fields and propose that these nonlinear structures play a key role in supporting parallel electric fields in the downward current region of the auroral zone.

FAST satellite observations during two encounters with the Earth's cusps near 4000 km are presented. In addition to precipitating magnetosheath particles with isotropic pitch angle distributions, the energetic particle data reveal upgoing ion beams, ion conics, downgoing “inverted‐V” electron distributions, and very narrow, intense upgoing electron beams. A rich assortment of DC‐coupled electric fields and plasma waves accompany these acceleration processes. In one example, step‐like injections of magnetosheath ions are correlated with bursts of upgoing ion beams and downgoing electrons, suggesting that the currents associated with these injections set up local electric potential structures that subsequently drive the acceleration processes. The observations underscore the fact that the cusp is not merely a conduit for the passage of magnetosheath particles and fields, but contains a dynamic internal electrical structure that accelerates particles locally and may alter the precipitating magnetosheath particle populations themselves.

The Fast Auroral SnapshoT (FAST) satellite has made observations in the Auroral Kilometric Radiation (AKR) source region with unprecedented frequency and time resolution. We confirm the AKR source is in a density depleted cavity and present examples in which cold electrons appeared to have been nearly evacuated (nhot> ncold). Electron distributions were depleted at low‐energies and up‐going ion beams were always present. Source region amplitudes were far greater than previously reported, reaching 2×10−4 (V/m)²/Hz (300 mV/m) in short bursts with bandwidths generally <1 kHz. Intense emissions were often at the edge of the density cavity. Emissions were near or below the cold plasma electron cyclotron frequency in the source region, and were almost entirely electromagnetic. The |E|/|B| ratio was constant as a function of frequency and rarely displayed any features that would identify a cold plasma cutoff or resonance.

Electric field and energetic particle observations by the Fast Auroral Snapshot (FAST) satellite provide convincing evidence of particle acceleration by quasi‐static, magnetic‐field‐aligned (parallel) electric fields in both the upward and downward current regions of the auroral zone. We demonstrate this by comparing the inferred parallel potentials of electrostatic shocks with particle energies. We also report nonlinear electric field structures which may play a role in supporting parallel electric fields. These structures include large‐amplitude ion cyclotron waves in the upward current region, and intense, spiky electric fields in the downward current region. The observed structures had substantial parallel components and correlative electron flux modulations. Observations of parallel electric fields in two distinct plasmas suggest that parallel electric fields may be a fundamental particle acceleration mechanism in astrophysical plasmas.

Upward flowing field‐aligned ion beams over auroral arcs have been observed with the 3‐dimensional ion mass spectrograph TEAMS on FAST. We have performed a statistical study on a sample of 77 ion beams from the auroral campaign in early 1997. All observed beams contain substantial amounts of H+, He+ and O+. A clear ordering of the total energies according to mass is found, with H+ having the lowest and O+ the highest energy. The composition varies significantly from beam to beam, with O+/H+ ratios ranging from ≈ 0.1 to 10. No variation of the energy ratio between species is observed as a function of relative abundance. These results are discussed in the light of earlier observations of higher energies for O+ in statistical studies of beams during solar minimum and attempts to explain this behavior in terms of beam instabilities.

FAST observes signatures of small‐scale downward‐going current at the edges of the inverted‐V regions where the primary (auroral) electrons are found. In the winter pre‐midnight auroral zone these downward currents are carried by upward flowing low‐ and medium‐energy (up to several keV) electron beams. FAST instrumentation shows agreement between the current densities inferred from both the electron distributions and gradients in the magnetic field. FAST data taken near apogee (∼4000‐km altitude) commonly show downward current magnetic field deflections consistent with the observed upward flux of ∼109 electrons cm−2 s−1, or current densities of several µA m−2. The electron, field‐aligned current and electric field signatures indicate the downward currents may be associated with “black aurora” and auroral ionospheric cavities. The field‐aligned voltage‐current relationship in the downward current region is nonlinear.

A technique is developed for analyzing remote measurements made by a single spacecraft of two dimensional disturbances in the ambient magnetosheath or magnetospheric magnetic field, caused, for example, by flux transfer events or pressure pulses. The methodology is based on a recent linear theory for isentropic field‐aligned MHD flow over gently sloping two‐dimensional obstacles (Sonnerup et al., 1992). Using only magnetic field measurements, the analysis technique can provide information about the orientation and actual cross‐sectional shape of the event, as well as information about the spacecraft trajectory relative to the bulge. If three‐dimensional plasma velocity measurements are also available, the technique provides the velocity and size of the event as well, and it allows one to determine whether the current sources causing the disturbance were in fact located on the side of the spacecraft trajectory facing the magnetopause. Analysis of two sample events, one recorded by the spacecraft AMPTE/IRM (Active Magnetospheric Particle Tracer Explorer/Ion Release Module) in the magnetosheath and the other by AMPTE/CCE (Charge Composition Explorer) in the magnetosphere, indicates that the bulges on the magnetopause surface causing the magnetic field and flow perturbations for these events did not have the semicircular cross section suggested in previous work; instead they had a more elongated shape, the dimension tangential to the magnetopause being substantially larger than that normal to it. The calculated invariant axes of the two events were found to differ substantially from the corresponding minimum variance directions of the measured magnetic field. The IRM event was found to move at a speed of 227 km/s away from the subsolar region. For the CCE event, plasma flow data were not available, but it was deduced indirectly that the event moved at a speed of about 90 km/s, presumably away from the subsolar region.

By using AMPTE/CCE energetic particle data, 167 ion injections that are essentially dispersionless over a nominal energy range of 25 keV to 285 keV have been cataloged. The ion, electron, and magnetic field signatures of these events are the kind normally associated with substorms in the near‐Earth magnetotail. We have examined the total magnetic field strength variations over the course of these events to identify the dependence on dipole latitude. The change in is poorly correlated with magnetic latitude. We interpret this result as indicating that during periods of substorm activity, the latitudinal position of the current sheet varies significantly within the 32° wedge centered on the dipole equator traversed by CCE. On the other hand, the changes in are well correlated with the local field properties themselves. This study therefore indicates that even in the near‐Earth magnetotail out to 8.8 RE (CCE apogee), the local field measurements are a better guide to the determination of one's position relative to the current sheet during a substorm than the magnetic latitude. Statistical relationships between Δ and both and |Bx| (in GSM coordinates) are consistent with the changes in that one would expect from a disruption/diversion of the cross‐tail current. The radial gradient of the reduction of the cross‐tail current during substorms appears to be negative, although the evidence is not conclusive. Finally, the local time variation of the statistical relationships is consistent with Birkeland current segments of the substorm current wedge which have a large extent in local time.

The concentrations of O(+) and NO(+) in the dayside high-latitude cleft region of the ionosphere are investigated based on synoptic particle and plasma measurements obtained by the polar orbiting Aeros-B and Isis-2 satellites. At a time when the orbital planes of the satellites are almost at right angles to each other, three maxima in ion temperature are observed, with two of them accompanied by an increased electron temperature and electron density irregularities, and the density of the molecular ions NO(+) and O2(+) is found to increase at the expense of O(+) density. Results are discussed in terms of a theory relating perpendicular electric fields to oxygen atom reaction rates. Systematic analysis of the Aeros data base reveals 14 additional instances of O(+) to NO(+) conversion, with a large variety of forms and structures reflecting the complex structure and dynamics of the high-latitude dayside ionosphere.

The two plasma experiments aboard the AFROS-B satellite determined the main plasma quantities in the height range 220-880km. These complementary instruments, a Retarding Potential Analyser and an Impedance Probe, provided the electron and ion temperatures, the main ion constitutents, the suprathermal electron flux and the plasma density.This paper summarizes a selection of the obtained results. Comparisons of several quantities with other observations demonstrate the high reliability of the AFROS plasma data. As a contribution to sensor theory a dependence of RPA measurements on the magnetic field vector has been established. The ion temperature and composition turn out to undergo a strong latitudinal variation, the highest hydrogen concentration in the upper atmosphere being located at ±20° latitude. Concerning the longitudinal variation of electron density discrepancies between measured data and existing models have been revealed. The statistical relation between the position of the mid-latitude trough and magnetic activity was studied for a fixed local time. First results of a synoptic study of the high latitude day-side ionosphere using AFROS-B and ISIS-II data are presented.