234 results found
Wilder FD, Schwartz SJ, Ergun RE, et al., 2020, Parallel Electrostatic Waves Associated With Turbulent Plasma Mixing in the Kelvin-Helmholtz Instability, GEOPHYSICAL RESEARCH LETTERS, Vol: 47, ISSN: 0094-8276
Starkey M, Fuselier SA, Desai MI, et al., 2020, MMS Observations of Accelerated Interstellar Pickup He(+)Ions at an Interplanetary Shock, ASTROPHYSICAL JOURNAL, Vol: 897, ISSN: 0004-637X
Madanian H, Schwartz SJ, Halekas JS, et al., 2020, Nonstationary Quasiperpendicular Shock and Ion Reflection at Mars, GEOPHYSICAL RESEARCH LETTERS, Vol: 47, ISSN: 0094-8276
Wilson LB, Chen L-J, Wang S, et al., 2020, Electron Energy Partition across Interplanetary Shocks. III. Analysis, ASTROPHYSICAL JOURNAL, Vol: 893, ISSN: 0004-637X
Gingell I, Schwartz SJ, Eastwood JP, et al., 2020, Statistics of reconnecting current sheets in the transition region of earth's bow shock, Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-14, ISSN: 2169-9380
We have conducted a comprehensive survey of burst mode observations of Earth's bow shock by the Magnetospheric Multiscale mission to identify and characterize current sheets associated with collisionless shocks, with a focus on those containing fast electron outflows, a likely signature of magnetic reconnection. The survey demonstrates that these thin current sheets are observed within the transition region of approximately 40% of shocks within the burst mode data set of Magnetospheric Multiscale. With only small apparent bias toward quasi‐parallel shock orientations and high Alfvén Mach numbers, the results suggest that reconnection at shocks is a universal process, occurring across all shock orientations and Mach numbers. On examining the distributions of current sheet properties, we find no correlation between distance from the shock, sheet width, or electron jet speed, though the relationship between electron and ion jet speed supports expectations of electron‐only reconnection in the region. Furthermore, we find that robust heating statistics are not separable from background fluctuations, and thus, the primary consequence of reconnection at shocks is in relaxing the topology of the disordered magnetic field in the transition region.
Hoilijoki S, Ergun RE, Schwartz SJ, et al., 2019, Electron-Scale Magnetic Structure Observed Adjacent to an Electron Diffusion Region at the Dayside Magnetopause, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10153-10169, ISSN: 2169-9380
Ergun RE, Hoilijoki S, Ahmadi N, et al., 2019, Magnetic Reconnection in Three Dimensions: Observations of Electromagnetic Drift Waves in the Adjacent Current Sheet, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10104-10118, ISSN: 2169-9380
Ergun RE, Hoilijoki S, Ahmadi N, et al., 2019, Magnetic Reconnection in Three Dimensions: Modeling and Analysis of Electromagnetic Drift Waves in the Adjacent Current Sheet, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10085-10103, ISSN: 2169-9380
Wilson LB, Chen L-J, Wang S, et al., 2019, Electron Energy Partition across Interplanetary Shocks. II. Statistics, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 245, ISSN: 0067-0049
Schwartz SJ, Andersson L, Xu S, et al., 2019, Collisionless Electron Dynamics in the Magnetosheath of Mars, GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 11679-11688, ISSN: 0094-8276
Starkey MJ, Fuselier SA, Desai M, et al., 2019, Acceleration of Interstellar Pickup He+ at Earth's Perpendicular Bow Shock, GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 10735-10743, ISSN: 0094-8276
Fowler CM, Halekas J, Schwartz S, et al., 2019, The Modulation of Solar Wind Hydrogen Deposition in the Martian Atmosphere by Foreshock Phenomena, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 7086-7097, ISSN: 2169-9380
Shuster JR, Gershman DJ, Chen L-J, et al., 2019, MMS Measurements of the Vlasov Equation: Probing the Electron Pressure Divergence Within Thin Current Sheets, GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 7862-7872, ISSN: 0094-8276
Wilson LB, Chen L-J, Wang S, et al., 2019, Electron Energy Partition across Interplanetary Shocks. I. Methodology and Data Product, ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, Vol: 243, ISSN: 0067-0049
Cohen IJ, Schwartz SJ, Goodrich KA, et al., 2019, High-Resolution Measurements of the Cross-Shock potential, Ion Reflection, and Electron Heating at an Interplanetary Shock by MMS, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 3961-3978, ISSN: 2169-9380
Goodrich KA, Ergun R, Schwartz SJ, et al., 2019, Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 1855-1865, ISSN: 2169-9380
Gingell I, Schwartz SJ, Eastwood JP, et al., 2019, Observations of magnetic reconnection in the ransition region of quasi-parallel hocks, Geophysical Research Letters, Vol: 46, Pages: 1177-1184, ISSN: 0094-8276
Using observations of Earth's bow shock by the Magnetospheric Multiscale mission, we show for the first time that active magnetic reconnection is occurring at current sheets embedded within the quasi‐parallel shock's transition layer. We observe an electron jet and heating but no ion response, suggesting we have observed an electron‐only mode. The lack of ion response is consistent with simulations showing reconnection onset on sub‐ion time scales. We also discuss the impact of electron heating in shocks via reconnection.
Johlander A, Vaivads A, Khotyaintsev YV, et al., 2018, Shock ripples observed by the MMS spacecraft: ion reflection and dispersive properties, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 60, ISSN: 0741-3335
Schwartz SJ, Avanov L, Turner D, et al., 2018, Ion kinetics in a hot flow anomaly: MMS observations, Geophysical Research Letters, Vol: 45, Pages: 11520-11529, ISSN: 0094-8276
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.
Goodrich KA, Ergun R, Schwartz SJ, et al., 2018, MMS Observations of Electrostatic Waves in an Oblique Shock Crossing, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 123, Pages: 9430-9442, ISSN: 2169-9380
Bandyopadhyay R, Chasapis A, Chhiber R, et al., 2018, Solar Wind Turbulence Studies Using MMS Fast Plasma Investigation Data, ASTROPHYSICAL JOURNAL, Vol: 866, ISSN: 0004-637X
Turner DL, Wilson LB, Liu TZ, et al., 2018, Autogenous and efficient acceleration of energetic ions upstream of Earth's bow shock, NATURE, Vol: 561, Pages: 206-+, ISSN: 0028-0836
Gingell IL, Schwartz SJ, Gershman DJ, et al., 2018, Production of negative hydrogen ions within MMS Fast Plasma Investigation due to solar wind bombardment, Journal of Geophysical Research: Space Physics, Vol: 123, Pages: 6161-6170, ISSN: 2169-9380
The particle data delivered by Fast Plasma Investigation (FPI) instrument aboard NASA's Magnetospheric Multiscale (MMS) mission allows for exceptionally high-resolution examination of the electron and ion phase space in the near-Earth plasma environment. It is necessary to identify populations which originate from instrumental effects. Using FPI's Dual Electron Spectrometers (DES) we isolate a high energy (~keV) beam, present while the spacecraft are in the solar wind, which exhibits an azimuthal drift with period associated with the spacecraft spin. We show that this population is consistent with negative hydrogen ions H- generated by a double charge exchange interaction between the incident solar wind H+ ions and the metallic surfaces within the instrument. This interaction is likely to occur at the deflector plates close to the instrument aperture. The H- density is shown to be approximately 0.2-0.4% of the solar wind ion density, and the energy of the negative ion population is shown to be 70% of the incident solar wind energy. These negative ions may introduce errors in electron velocity moments on the order of 0.2-0.4% of the solar wind velocity, and significantly higher errors in the electron temperature.
Chen L-J, Wang S, Wilson LB, et al., 2018, Electron Bulk Acceleration and Thermalization at Earth's Quasiperpendicular Bow Shock., Phys Rev Lett, Vol: 120
Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating.
Eastwood J, Mistry R, Phan TD, et al., 2018, Guide field reconnection: exhaust structure and heating, Geophysical Research Letters, Vol: 45, Pages: 4569-4577, ISSN: 0094-8276
Magnetospheric Multiscale (MMS) observations are used to probe the structure and temperature profile of a guide field reconnection exhaust ~100 ion inertial lengths downstream from the X‐line in the Earth's magnetosheath. Asymmetric Hall electric and magnetic field signatures were detected, together with a density cavity confined near one edge of the exhaust and containing electron flow toward the X‐line. Electron holes were also detected both on the cavity edge and at the Hall magnetic field reversal. Predominantly parallel ion and electron heating was observed in the main exhaust but within the cavity, electron cooling and enhanced parallel ion heating was found. This is explained in terms of the parallel electric field, which inhibits electron mixing within the cavity on newly reconnected field lines, but accelerates ions. Consequently, guide field reconnection causes inhomogeneous changes in ion and electron temperature across the exhaust.
Ergun RE, Goodrich KA, Wilder FD, et al., 2018, Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail, Geophysical Research Letters, Vol: 45, Pages: 3338-3347, ISSN: 0094-8276
We report observations of turbulent dissipation and particle acceleration from large-amplitude electric fields (E) associated with strong magnetic field (B) fluctuations in the Earth's plasma sheet. The turbulence occurs in a region of depleted density with anti-earthward flows followed by earthward flows suggesting ongoing magnetic reconnection. In the turbulent region, ions and electrons have a significant increase in energy, occasionally > 100 keV, and strong variation. There are numerous occurrences of |E| > 100 mV/m including occurrences of large potentials ( > 1 kV) parallel to B and occurrences with extraordinarily large J · E (J is current density). In this event, we find that the perpendicular contribution of J · E with frequencies near or below the ion cyclotron frequency (f ci ) provide the majority net positive J · E. Large-amplitude parallel E events with frequencies above f ci to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration.
Gershman DJ, F-Vinas A, Dorelli JC, et al., 2018, Energy partitioning constraints at kinetic scales in low-beta turbulence, PHYSICS OF PLASMAS, Vol: 25, ISSN: 1070-664X
Broll JM, Fuselier SA, Trattner KJ, et al., 2018, MMS Observation of Shock-Reflected He++ at Earth's Quasi-Perpendicular Bow Shock, GEOPHYSICAL RESEARCH LETTERS, Vol: 45, Pages: 49-55, ISSN: 0094-8276
Mejnertsen L, Eastwood J, Hietala H, et al., 2017, Global MHD simulations of the Earth's bow shock shape and motion under variable solar wind conditions, Journal of Geophysical Research: Space Physics, Vol: 123, Pages: 259-271, ISSN: 2169-9380
Empirical models of the Earth's bow shock are often used to place in situ measurements in context and to understand the global behavior of the foreshock/bow shock system. They are derived statistically from spacecraft bow shock crossings and typically treat the shock surface as a conic section parameterized according to a uniform solar wind ram pressure, although more complex models exist. Here a global magnetohydrodynamic simulation is used to analyze the variability of the Earth's bow shock under real solar wind conditions. The shape and location of the bow shock is found as a function of time, and this is used to calculate the shock velocity over the shock surface. The results are compared to existing empirical models. Good agreement is found in the variability of the subsolar shock location. However, empirical models fail to reproduce the two-dimensional shape of the shock in the simulation. This is because significant solar wind variability occurs on timescales less than the transit time of a single solar wind phase front over the curved shock surface. Empirical models must therefore be used with care when interpreting spacecraft data, especially when observations are made far from the Sun-Earth line. Further analysis reveals a bias to higher shock speeds when measured by virtual spacecraft. This is attributed to the fact that the spacecraft only observes the shock when it is in motion. This must be accounted for when studying bow shock motion and variability with spacecraft data.
Gingell IL, Schwartz SJ, Burgess D, et al., 2017, MMS observations and hybrid simulations of surface ripples at a marginally quasi-parallel shock, Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 11003-11017, ISSN: 2169-9380
Simulations and observations of collisionless shocks have shown that deviations of the nominal local shock normal orientation, i.e. surface waves or ripples, are expected to propagate in the ramp and overshoot of quasi-perpendicular shocks. Here, we identify signatures of a surface ripple propagating during a crossing of Earth's marginally quasi-parallel (θBn∼45∘) or quasi-parallel bow shock shock on 2015-11-27 06:01:44 UTC by the Magnetospheric Multiscale (MMS) mission, and determine the ripple's properties using multi-spacecraft methods. Using two-dimensional hybrid simulations, we confirm that surface ripples are a feature of marginally quasi-parallel and quasi-parallel shocks under the observed solar wind conditions. In addition, since these marginally quasi-parallel and quasi-parallel shocks are expected to undergo a cyclic reformation of the shock front, we discuss the impact of multiple sources of non-stationarity on shock structure. Importantly, ripples are shown to be transient phenomena, developing faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change in properties of the ripple observed by MMS is consistent with the reformation of the shock front over a timescale of an ion gyro-period.
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