Electromagnetic ion cyclotron (EMIC) waves at large L shells were observed away from the magnetic equator by the Magnetospheric MultiScale (MMS) mission nearly continuously for over four hours on 28 ...October 2015. During this event, the wave Poynting vector direction systematically changed from parallel to the magnetic field (toward the equator), to bidirectional, to antiparallel (away from the equator). These changes coincide with the shift in the location of the minimum in the magnetic field in the southern hemisphere from poleward to equatorward of MMS. The local plasma conditions measured with the EMIC waves also suggest that the outer magnetospheric region sampled during this event was generally unstable to EMIC wave growth. Together, these observations indicate that the bidirectionally propagating wave packets were not a result of reflection at high latitudes but that MMS passed through an off‐equator EMIC wave source region associated with the local minimum in the magnetic field.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) waves are a fundamental plasma instability in space environments. In near‐Earth space, these waves act as one mechanism for energetic electrons in the radiation belts to be lost to the atmosphere. Because EMIC waves are important for the transport of energy throughout the magnetosphere, understanding where and how these waves are generated, as well as how the waves move along a magnetic field line, is necessary for understanding the full cycle of energization and loss of plasma. The two previous case studies of EMIC waves at high latitudes in the outer magnetosphere were not able to determine if the waves were generated at those high latitudes or if the wave signatures were due to reflection of the waves back toward the magnetic equator, which has important implications for waves seen from the ground. The observations presented here show EMIC waves in the outer magnetosphere away from the equator nearly continuously over several hours. Using the wave Poynting flux direction (which indicates how the waves are moving along the magnetic field), we show unambiguously for the first time that these EMIC waves are from a local source region at higher latitudes.
Key Points
Several hours of EMIC wave activity were observed off‐equator in the outer magnetosphere with plasma conditions favorable for local growth
Changes in direction of the wave Poynting vector indicate transition of source region from poleward, to local, to equatorward of spacecraft
Observations confirm association of EMIC wave source region with local minimum‐B of the field line, possibly related to Shabansky orbits
We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft ...partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.
Understanding the physical mechanisms responsible for the cross‐scale energy transport and plasma heating from solar wind into the Earth's magnetosphere is of fundamental importance for ...magnetospheric physics and for understanding these processes in other places in the universe with comparable plasma parameter ranges. This paper presents observations from the Magnetosphere Multiscale (MMS) mission at the dawn‐side high‐latitude dayside boundary layer on February 25, 2016 between 18:55 and 20:05 UT. During this interval, MMS encountered both the inner and outer boundary layers with quasiperiodic low frequency fluctuations in all plasma and field parameters. The frequency analysis and growth rate calculations are consistent with the Kelvin‐Helmholtz instability (KHI). The intervals within the low frequency wave structures contained several counter‐streaming, low‐ (0–200 eV) and mid‐energy (200 eV–2 keV) electrons in the loss cone and trapped energetic (70–600 keV) electrons in alternate intervals. The counter‐streaming electron intervals were associated with large‐magnitude field‐aligned Poynting fluxes. Burst mode data at the large Alfvén velocity gradient revealed a strong correlation between counter streaming electrons, enhanced parallel electron temperatures, strong anti‐field aligned wave Poynting fluxes, and wave activity from sub‐proton cyclotron frequencies extending to electron cyclotron frequency. Waves were identified as Kinetic Alfvén waves but their contribution to parallel electron heating was not sufficient to explain the >100 eV electrons, and rapid nonadiabatic heating of the boundary layer as determined by the characteristic heating frequency, derived here for the first time.
Plain Language Summary
Electrons, The Riders of the Space Hurricane: Earth's magnetic field forms a barrier in the solar wind, called the magnetosphere, which provides some shielding against solar radiation and galactic cosmic rays. However, this shield can be penetrated by process called magnetic reconnection, and secondary processes created by giant "fluid‐scale" space hurricanes (typically 20,000–36,000 km in wave length) aka Kelvin‐Helmholtz (KH) waves that are whipped along the magnetic barrier by solar wind flow. One of the puzzling problems of the Earth's magnetosphere is that it is so hot: both electrons and ions are heated to tens of millions of degrees when they get transported from solar wind through the Earth's magnetic barrier. This article shows observations of multiscale wave structures, spanning the fluid‐scales, ion scales and electron scales detected by the NASA's magnetosphere multiscale mission consisting of four satellites. We show how these large‐scale waves contain ion and electron scale waves that are able to produce some of the observed electron heating and acceleration. We "fingerprint" the exact plasma wave modes (tornadoes) inside the space hurricane that are responsible for resonantly whipping and transferring the wave energy to the electrons surfing the wave.
Key Points
Magnetosphere multiscale observed periodic low frequency waves, likely Kelvin‐Helmholtz instability, at the dawn‐flank high‐latitude boundary layer
Higher frequency waves within the low frequency waves were associated with enhanced Poynting flux and parallel electron heating
Waves close to proton cyclotron frequency were identified as Kinetic Alfvén waves, and were evaluated to provide partial heating
We report Magnetospheric Multiscale observations of reconnection in a thin current sheet at the interface of interlinked flux tubes carried by converging reconnection jets at Earth's magnetopause. ...The ion skin depth‐scale width of the interface current sheet and the non‐frozen‐in ions indicate that Magnetospheric Multiscale crossed the reconnection layer near the X‐line, through the ion diffusion region. Significant pileup of the reconnecting component of the magnetic field in this and three other events on approach to the interface current sheet was accompanied by an increase in magnetic shear and decrease in Δβ, leading to conditions favorable for reconnection at the interface current sheet. The pileup also led to enhanced available magnetic energy per particle and strong electron heating. The observations shed light on the evolution and energy release in 3‐D systems with multiple reconnection sites.
Plain Language Summary
The Earth and the solar wind magnetic fields interconnect through a process called magnetic reconnection. The newly reconnected magnetic field lines are strongly bent and accelerate particles, similar to a rubber band in a slingshot. In this paper we have used observations from NASA's Magnetospheric MultiScale spacecraft to investigate what happens when two of these slingshot‐like magnetic field lines move toward each other and get tangled up. We found that the two bent magnetic field lines tend to orient themselves perpendicular to each other as they become interlinked and stretched, similar to what rubber bands would do. This reorientation allows the interlinked magnetic fields to reconnect again, releasing part of the built‐up magnetic energy as strong electron heating. The results are important because they show how interlinked magnetic fields, which occur in many solar and astrophysics contexts, reconnect and produce enhanced electron heating, something that was not understood before.
Key Points
Magnetic flux pileup observed upstream of reconnecting current sheet at the interface of converging reconnection jets
Magnetic flux pileup was accompanied by increase in magnetic shear and decrease in Δβ, leading to conditions favorable for reconnection
Magnetic flux pileup leads to enhanced available magnetic energy per particle and strong electron heating
Factors related to two sources of energy input to the ionosphere, the Poynting flux associated with both quasistatic fields (Sdc) and Alfvénic fluctuations (Sac), and the soft electron precipitation, ...are investigated to evaluate their correlations with the O+ and the H+ outflows in the dayside cusp region by using recalibrated FAST/Time‐of‐Flight Energy, Angle, and Mass Spectrograph (TEAMS) data during the 24–25 September 1998 geomagnetic storm studied by Strangeway et al. (2005, https://doi.org/10.1029/2004JA010829). The Poynting flux and the soft electron precipitation are well correlated with ion outflow flux in the dayside cusp region. Sdc shows the highest correlation with the O+ outflows, while it is the electron number flux that correlates best with the H+ outflows. The Alfvénic waves play an essential role in accelerating outflows. The averaged O+/H+ flux ratio is 3.0 and is positively correlated to the Poynting flux, suggesting that the O+ flux increases more strongly with the energy input.
Plain Language Summary
Ionospheric outflows are a major plasma source for the Earth's magnetosphere, especially during geomagnetic storms. Various parameters related to the electromagnetic energy input, the electron precipitation, and the extremely low frequency plasma waves are used to investigate their correlations with ion outflows in the dayside cusp region during the 24–25 September 1998 geomagnetic storm. We first recalibrated the data from the FAST/Time‐of‐Flight Energy, Angle, and Mass Spectrograph (TEAMS) instrument before using it. The electromagnetic energy has the highest correlations with the oxygen ion outflows, while it is the electron precipitation for proton outflows. The energy input associated with Alfvén waves also shows strong correlations. Maxima of the energy input show better correlations than the averages. The oxygen ion is the dominant outflow species in this storm with an average flux ratio of 3.0 to proton outflows. A higher ratio is observed with more energy input to the Earth's ionosphere.
Key Points
The best controlling factor for driving O+ and H+ outflows is quasistatic Poynting flux and soft electron precipitation, respectively
The averaged O+/H+ flux ratio is 3.0 over the cusp region. The ratio is positively correlated to energy input to the ionosphere
The Poynting flux associated with Alfvén waves also shows strong correlation with outflows in the dayside cusp region
Data acquired by the Fast Auroral Snapshot (FAST) Small Explorer during the 24–25 September 1998 geomagnetic storm have been used to determine the controlling parameters for ionospheric outflows. The ...data were restricted to dayside magnetic local times. Two primary sources of ion outflows are considered: ion heating through dissipation of downward Poynting flux and electron heating through soft electron precipitation. Ion outflows are shown to be correlated with both, although ion outflows have a higher correlation with soft electrons, measured by the density of precipitating electrons. At 4000 km altitude it is found that fi = 1.022 × 109±0.341nep2.200±0.489, where fi is the ion flux in cm−2 s−1 and nep is precipitating electron density, with a correlation coefficient r = 0.855, based on log‐log regression. This scaling law can be mapped to other altitudes by scaling the flux and density with the magnetic field magnitude. The ion flux is also correlated with the Poynting flux, fi = 2.142 × 107±0.242S1.265±0.445, where S is the Poynting flux at 4000 km altitude in mW m−2 and r = 0.721. Either of these two scaling laws can be used specify ion outflow fluxes, since there is a strong intercorrelation between the various parameters. In particular the present study cannot completely eliminate either of the two candidate processes (ion versus electron heating in the ionosphere, corresponding to Poynting flux versus soft electron precipitation). Soft electron precipitation does have a higher correlation coefficient, however, and if possible the precipitating electron density scaling law should be used. Since Poynting flux may be more easily specified in global simulations, for example, this scaling law is a useful alternate. For the interval under study the ion outflows were dominated by oxygen ions, predominantly in the form of ion conics, with a characteristic energy of order 10–30 eV.
The Magnetospheric Multiscale (MMS) mission was designed to make observations in the very small electron diffusion region (EDR), where magnetic reconnection takes place. From a data set of over 4500 ...magnetopause crossings obtained in the first phase of the mission, MMS had encounters near or within 12 EDRs. These 12 events and associated magnetopause crossings are considered as a group to determine if they span the widest possible range of external and internal conditions (i.e., in the solar wind and magnetosphere). In addition, observations from MMS are used to determine if there are multiple X‐lines present and also to provide information on X‐line location relative to the spacecraft. These 12 events represent nearly the widest possible range of conditions at the dayside magnetopause. They occur over a wide range of local times and magnetic shear angles between the magnetosheath and magnetospheric magnetic fields. Most show evidence for multiple reconnection sites.
Key Points
MMS X‐line events cover a wide range of external conditions
Almost all X‐line events are associated with multiple X‐lines at the magnetopause
Reconnection between the magnetosheath and an existing boundary layer is required for KH instability
We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including ...Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m approximately 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single-frequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with step-like frequency changes along L. Each discrete L shell has a steady wave frequency and spans about 1 RE, suggesting that there exist a discrete number of drift-bounce resonance regions across L shells during storm times.
The recalibrated FAST/TEAMS data is used to study the response of O+ and H+ outflow to energy inputs in the nightside aurora during the 24–25 September 1998 geomagnetic storm, the same storm studied ...by Strangeway et al. (2005), https://doi.org/10.1029/2004JA010829. In contrast to the cusp, the Poynting flux and electron precipitation energy input are not as well correlated on the nightside, so their effects on outflow can be differentiated. The O+ outflow shows a strong correlation with both the Alfvénic Poynting flux (r = 0.71) and the soft electron precipitation (r = 0.69), while the H+ outflow only correlates well with the electron number flux (r = 0.74). This indicates that the auroral H+ outflow is close to its limiting flux without additional wave acceleration, while the outflow for the heavier O+ ion is increased by additional wave acceleration.
Plain Language Summary
Geomagnetic activity can cause electrons to precipitate into the ionosphere in the nightside auroral region. It can also deliver electromagnetic wave energy to the same region. The electron precipitation can both heat and further ionize the ionosphere, leading to ions moving up along the field line. The wave energy can further accelerate the ions. If the ions are accelerated enough by these processes, they will flow out along the magnetic field, escaping the ionosphere. This paper finds that the H+ outflow increases with increased precipitating electrons in the nightside aurora. The O+ outflow increases with both electron precipitation and wave acceleration.
Key Points
Electron precipitation and Poynting flux are less correlated on the nightside than the cusp, so their effects on outflow can be distinguished
O+ outflow is correlated with both Poynting flux and electron precipitation, while H+ is only correlated with electron precipitation
Parameterization of the outflow dependence is consistent between the dayside cusp and the nightside auroral regions
Plasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed ...using distribution functions comprising up to six drifting bi‐Maxwellian distributions. In both events electron crescent‐shaped distributions are shown to be responsible for upper hybrid waves near the X‐line. In an adjacent location within the 3 July event a monodirectional field‐aligned electron beam drove parallel‐propagating beam‐mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper‐hybrid and beam‐mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions.
Plain Language Summary
Magnetic reconnection is a process that occurs throughout the universe in ionized gases (plasmas) containing embedded magnetic fields. This process converts magnetic energy to electron and ion energy, causing phenomena such as solar flares and auroras. The NASA Magnetospheric Multiscale mission has shown that in magnetic reconnection regions there are intense electric field oscillations or waves and that electrons form crescent and beam‐like populations propagating both along and perpendicular to the magnetic field. This study shows that the observed electron populations are responsible for high‐frequency waves including their propagation directions and frequency ranges.
Key Points
Electron crescent‐shaped distributions produce upper hybrid waves in magnetotail reconnection events
Field‐aligned electron beams generate parallel electrostatic waves through the beam‐mode
Multiple crescent and convecting core distributions act together to produce broad frequency spectra as observed by MMS
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