The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission

Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi‐perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency ∼100 Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi‐perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05–0.2fce by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first‐time 3‐D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi‐linear pitch angle diffusion and possible signatures of nonlinear interaction with high‐amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes

Electron-scale measurements of magnetic reconnection in space

Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using very high time resolution measurements, NASA’s Magnetospheric Multiscale Mission (MMS) has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth’s magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy, (ii) measured the electric field and current, which together cause the dissipation of magnetic energy, and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region

Parker solar probe observations of solar wind energetic proton beams produced by magnetic reconnection in the near‐sun heliospheric current sheet

We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 Rs and 20 Rs, respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. Furthermore, protons were energized to super-thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust

Lower-hybrid drift waves and electromagnetic electron space-phase holes associated with dipolarization fronts and field-aligned currents observed by the Magnetospheric Multiscale mission during a substorm

We analyse two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on August 10, 2016. The first event corresponds to a fast dawnward flow with an anti-parallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower-hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing, and with a smaller lower-hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet, we cannot rule out the possibility that the drift waves are produced by the anti-parallel current associated with the fast flows, leaving the source for the electron holes unexplained

Relative efficacy of sildenafil compared to other treatment options for erectile dysfunction

Objective, We examined and compared the efficacy of sildenafil in patients previously using other agents or devices for erectile dysfunction (ED) treatment

Ion kinetics in a hot flow anomaly: MMS observations

Hot Flow Anomalies (HFAs) are transients observed at planetary bow shocks, formed by the shock interaction with a convected interplanetary current sheet. The primary interpretation relies on reflected ions channeled upstream along the current sheet. The short duration of HFAs has made direct observations of this process difficult. We employ high resolution measurements by NASA's Magnetospheric Multiscale Mission to probe the ion microphysics within a HFA. Magnetospheric Multiscale Mission data reveal a smoothly varying internal density and pressure, which increase toward the trailing edge of the HFA, sweeping up particles trapped within the current sheet. We find remnants of reflected or other backstreaming ions traveling along the current sheet, but most of these are not fast enough to out-run the incident current sheet convection. Despite the high level of internal turbulence, incident and backstreaming ions appear to couple gyro-kinetically in a coherent manner

MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause

©2016. American Geophysical Union. All Rights Reserved.We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earths magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (di) width) current sheet (at ~12 di downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection

Wave-particle energy exchange directly observed in a kinetic Alfven-branch wave

Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA’s Magnetospheric Multiscale (MMS) mission, we utilize Earth’s magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations