Publications
225 results found
Eastwood J, Phan T, Cassak PA, et al., 2016, Ion-scale secondary flux-ropes generated by magnetopause reconnection as resolved by MMS, Geophysical Research Letters, Vol: 43, Pages: 4716-4724, ISSN: 1944-8007
New Magnetospheric Multiscale (MMS) observations of small-scale (~ 7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10 km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multi-spacecraft techniques, allowing them to be identified as flux ropes, whose flux content is small (~22 kWb). The current density, calculated using plasma and magnetic field measurements independently, is found to be filamentary. Inter-comparison of the plasma moments with electric and magnetic field measurements reveals structured non-frozen-in ion behavior. The data are further compared with a particle-in-cell simulation. It is concluded that these small-scale flux ropes, which are not seen to be growing, represent a distinct class of FTE which is generated on the magnetopause by secondary reconnection.
Farrugia CJ, Lavraud B, Torbert RB, et al., 2016, Magnetospheric Multiscale Mission observations and non-force free modeling of a flux transfer event immersed in a super-Alfvénic flow, Geophysical Research Letters, Vol: 43, Pages: 6070-6077, ISSN: 0094-8276
We analyze plasma, magnetic field, and electric field data for a flux transfer event (FTE) to highlight improvements in our understanding of these transient reconnection signatures resulting from high-resolution data. The ∼20 s long, reverse FTE, which occurred south of the geomagnetic equator near dusk, was immersed in super-Alfvénic flow. The field line twist is illustrated by the behavior of flows parallel/perpendicular to the magnetic field. Four-spacecraft timing and energetic particle pitch angle anisotropies indicate a flux rope (FR) connected to the Northern Hemisphere and moving southeast. The flow forces evidently overcame the magnetic tension. The high-speed flows inside the FR were different from those outside. The external flows were perpendicular to the field as expected for draping of the external field around the FR. Modeling the FR analytically, we adopt a non-force free approach since the current perpendicular to the field is nonzero. It reproduces many features of the observations.
Ergun RE, Holmes JC, Goodrich KA, et al., 2016, Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause, Geophysical Research Letters, Vol: 43, Pages: 5626-5634, ISSN: 0094-8276
We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E||) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (<10 eV) plasma in the magnetosphere with warm (~100 eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause.
Krupar V, Eastwood JP, Kruparova O, et al., 2016, An analysis of interplanetary solar radio emissions associated with a coronal mass ejection, Astrophysical Journal Letters, Vol: 823, ISSN: 2041-8205
Coronal mass ejections (CMEs) are large-scale eruptions of magnetized plasma that may cause severe geomagnetic storms if Earth directed. Here, we report a rare instance with comprehensive in situ and remote sensing observations of a CME combining white-light, radio, and plasma measurements from four different vantage points. For the first time, we have successfully applied a radio direction-finding technique to an interplanetary type II burst detected by two identical widely separated radio receivers. The derived locations of the type II and type III bursts are in general agreement with the white-light CME reconstruction. We find that the radio emission arises from the flanks of the CME and are most likely associated with the CME-driven shock. Our work demonstrates the complementarity between radio triangulation and 3D reconstruction techniques for space weather applications.
Lavraud B, Zhang YC, Vernisse Y, et al., 2016, Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause, Geophysical Research Letters, Vol: 43, Pages: 3042-3050, ISSN: 1944-8007
Based on high-resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field-aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field-aligned potentials).
Phan TD, Shay MA, Eastwood JP, et al., 2016, Establishing the Context for Reconnection Diffusion Region Encounters and Strategies for the Capture and Transmission of Diffusion Region Burst Data by MMS, Space Science Reviews, Vol: 199, Pages: 631-650, ISSN: 0038-6308
© 2015, The Author(s). This paper describes the efforts of our Inter-Disciplinary Scientist (IDS) team to (a) establish the large-scale context for reconnection diffusion region encounters by MMS at the magnetopause and in the magnetotail, including the distinction between X-line and O-line encounters, that would help the identification of diffusion regions in spacecraft data, and (b) devise possible strategies that can be used by MMS to capture and transmit burst data associated with diffusion region candidates. At the magnetopause we suggest the strategy of transmitting burst data from all magnetopause crossings so that no magnetopause reconnection diffusion regions encountered by the spacecraft will be missed. The strategy is made possible by the MMS mass memory and downlink budget. In the magnetotail, it is estimated that MMS will be able to transmit burst data for all diffusion regions, all reconnection jet fronts (a.k.a. dipolarization fronts) and separatrix encounters, but less than 50 % of reconnection exhausts encountered by the spacecraft. We also discuss automated burst trigger schemes that could capture various reconnection-related phenomena. The identification of candidate diffusion region encounters by the burst trigger schemes will be verified and improved by a Scientist-In-The-Loop (SITL). With the knowledge of the properties of the region surrounding the diffusion region and the combination of automated burst triggers and further optimization by the SITL, MMS should be able to capture most diffusion regions it encounters.
Mistry R, Eastwood JP, Hietala H, 2015, Development of bifurcated current sheets in solar wind reconnection exhausts, Geophysical Research Letters, Vol: 42, Pages: 10513-10520, ISSN: 1944-8007
Petschek-type reconnection is expected to result in bifurcations of reconnection current sheets. In contrast, Hall reconnection simulations show smooth changes in the reconnecting magnetic field. Here we study three solar wind reconnection events where different spacecraft sample oppositely directed reconnection exhausts from a common reconnection site. The spacecraft's relative separations and measurements of the exhaust width are used to geometrically calculate each spacecraft's distance from the X line. We find that in all cases spacecraft farthest from the X line observe clearly bifurcated reconnection current sheets, while spacecraft nearer to the X line do not. These observations suggest that clear bifurcations of reconnection current sheets occur at large distances from the X line (~1000 ion skin depths) and that Petschek-type signatures are less developed close to the reconnection site. This may imply that fully developed bifurcations of reconnection current sheets are unlikely to be observed in the near-Earth magnetotail.
Russell AJB, Yeates AR, Eastwood JP, 2015, Magnetic reconnection now and in the future, Astronomy and Geophysics, Vol: 56, ISSN: 1366-8781
Arridge CS, Eastwood J, Jackman CM, et al., 2015, Cassini in situ observations of long duration magnetic reconnection in Saturn’s magnetotail, Nature Physics, Vol: 12, Pages: 268-271, ISSN: 1745-2481
Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy1, 2, 3, 4. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field5, 6. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn’s magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn6. This counters the view of reconnection as a transient method of internal plasma loss at Saturn5, 7. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies.
Palmroth M, Archer M, Vainio R, et al., 2015, ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 8782-8798, ISSN: 2169-9380
Hietala H, Drake JF, Phan TD, et al., 2015, Ion temperature anisotropy across a magnetotail reconnection jet, Geophysical Research Letters, Vol: 42, Pages: 7239-7247, ISSN: 1944-8007
A significant fraction of the energy released by magnetotail reconnection appears to go into ion heating, but this heating is generally anisotropic. We examine ARTEMIS dual-spacecraft observations of a long-duration magnetotail exhaust generated by anti-parallel reconnection in conjunction with Particle-In-Cell simulations, showing spatial variations in the anisotropy across the outflow far (> 100di) downstream of the X-line. A consistent pattern is found in both the spacecraft data and the simulations: Whilst the total temperature across the exhaust is rather constant, near the boundaries Ti,|| dominates. The plasma is well-above the firehose threshold within patchy spatial regions at |BX| ∈ [0.1, 0.5]B0, suggesting that the drive for the instability is strong and the instability is too weak to relax the anisotropy. At the mid-plane (|BX|0.1 B0), Ti,⊥ > Ti,|| and ions undergo Speiser-like motion despite the large distance from the X-line.
Eastwood J, 2015, Observing Magnetic Reconnection: The Influence of Jim Dungey, Magnetospheric Plasma Physics: The Impact of Jim Dungey’s Research, Editors: Southwood, Cowley, Mitton, Publisher: Springer, Pages: 181-197, ISBN: 9783319183589
This book makes good background reading for much of modern magnetospheric physics.
Horbury TS, Archer MO, Brown P, et al., 2015, The MAGIC of CINEMA: First in-flight science results from a miniaturised anisotropic magnetoresistive magnetometer, Annales Geophysicae, Vol: 33, Pages: 725-735, ISSN: 1432-0576
We present the first in-flight results from a novel miniaturised anisotropic magnetoresistive space magnetometer, MAGIC (MAGnetometer from Imperial College), aboard the first CINEMA (CubeSat for Ions, Neutrals, Electrons and MAgnetic fields) spacecraft in low Earth orbit. An attitude-independent calibration technique is detailed using the International Geomagnetic Reference Field (IGRF), which is temperature dependent in the case of the outboard sensor. We show that the sensors accurately measure the expected absolute field to within 2% in attitude mode and 1% in science mode. Using a simple method we are able to estimate the spacecraft's attitude using the magnetometer only, thus characterising CINEMA's spin, precession and nutation. Finally, we show that the outboard sensor is capable of detecting transient physical signals with amplitudes of ~ 20–60 nT. These include field-aligned currents at the auroral oval, qualitatively similar to previous observations, which agree in location with measurements from the DMSP (Defense Meteorological Satellite Program) and POES (Polar-orbiting Operational Environmental Satellites) spacecraft. Thus, we demonstrate and discuss the potential science capabilities of the MAGIC instrument onboard a CubeSat platform.
Balogh A, Bykov A, Eastwood J, et al., 2015, Multi-scale Structure Formation and Dynamics in Cosmic Plasmas, SPACE SCIENCE REVIEWS, Vol: 188, Pages: 1-2, ISSN: 0038-6308
Eastwood JP, Hietala H, Toth G, et al., 2015, What Controls the Structure and Dynamics of Earth's Magnetosphere?, SPACE SCIENCE REVIEWS, Vol: 188, Pages: 251-286, ISSN: 0038-6308
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- Citations: 36
Eastwood JP, Goldman MV, Hietala H, et al., 2015, Ion reflection and acceleration near magnetotail dipolarization fronts associated with magnetic reconnection, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 511-525, ISSN: 2169-9402
Dipolarization fronts (DFs) are often associated with the leading edge of earthward bursty bulk flows in the magnetotail plasma sheet. Here multispacecraft Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations are used to show that a spatially limited region of counterpropagating ion beams, whose existence is not evident in either the plasma moments or the electric field, is observed on the low-density side of DFs. The THEMIS magnetic field data are used to establish appropriate comparison cuts through a particle-in-cell simulation of reconnection, and very good agreement is found between the observed and simulated ion distributions on both sides of the DF. Self-consistent back tracing shows that the ion beams originate from the thermal component of the preexisting high-density plasma into which the DF is propagating; they do not originate from the inflow region in the traditional sense. Forward tracing shows that some of these ions can subsequently overtake the DF and pass back into the high-density preexisting plasma sheet with an order-of-magnitude increase in energy; this process is distinct from other ion reflection processes that occur directly at the DF. The interaction of the reconnection jet with the preexisting plasma sheet therefore occurs over a macroscopic region, rather than simply being limited to the thin DF interface. A more general consequence of this study is the conclusion that reconnection jets are not simply fed by plasma inflow across the separatrices but are also fed by plasma from the region into which the jet is propagating; the implications of this finding are discussed.
Eastwood JP, Kiehas SA, 2015, Origin and Evolution of Plasmoids and Flux Ropes in the Magnetotails of Earth and Mars, Magnetotails in the Solar System, Pages: 269-287, ISBN: 9781118842348
This chapter discusses the origin and evolution of plasmoids and flux ropes in Earth's magnetotail, providing an overview of author's current understanding based on recent multipoint and multimission data analysis. It also presents recent results concerning observations of flux ropes in the vicinity of Mars. Understanding the Mars solar wind interaction is very important for determining its atmospheric history, and recent discoveries show that magnetic reconnection-generated structures may play a significant role, particularly in the vicinity of the crustal field regions. The chapter briefly discusses some of the different terms used to describe reconnection-generated structures. It describes the production of islands, plasmoids, and secondary islands by antiparallel reconnection.
Eastwood JP, Kataria DO, McInnes CR, et al., 2015, Sunjammer, WEATHER, Vol: 70, Pages: 27-30, ISSN: 0043-1656
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- Citations: 10
Brown P, Whiteside BJ, Beek TJ, et al., 2014, Space magnetometer based on an anisotropic magnetoresistive hybrid sensor, Review of Scientific Instruments, Vol: 85, ISSN: 1089-7623
Mistry R, Eastwood JP, Hietala H, 2014, Detection of small-scale folds at a solar wind reconnection exhaust, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 30-42, ISSN: 2169-9402
Observations of reconnection in the solar wind over the last few years appear to indicate that the majority of large-scale reconnecting current sheets are roughly planar, and that reconnection itself is quasi-steady. Most studies of solar wind exhausts have used spacecraft with large separations and relatively low time cadence ion measurements. Here we present multipoint Cluster observations of a reconnection exhaust and the associated current sheet at ACE and Wind, enabling it to be studied on multiple length scales and at high time resolution. While analysis shows that on large scales the current sheet is planar, detailed measurements using the four closely spaced Cluster spacecraft show that the trailing edge of the reconnection jet is nonplanar with folds orthogonal to the reconnection plane, with length scales of approximately 230 ion inertial lengths. Our findings thus suggest that while solar wind current sheets undergoing reconnection may be planar on large scales, they may also exhibit complex smaller-scale structure. Such structure is difficult to observe and has rarely been detected because exhausts are rapidly convected past the spacecraft in a single cut; there is therefore a limited set of spacecraft trajectories through the exhaust which would allow the nonplanar features to be intercepted. We consider how such nonplanar reconnection current sheets can form and the processes which may have generated the 3-D structure that was observed.
Archer MO, Turner DL, Eastwood JP, et al., 2014, Global impacts of a Foreshock Bubble: Magnetosheath, magnetopause and ground-based observations, Planetary and Space Science, Vol: 106, Pages: 56-66, ISSN: 1873-5088
Using multipoint observations we show, for the first time, that Foreshock Bubbles (FBs) have a global impact on Earth׳s magnetosphere. We show that an FB, a transient kinetic phenomenon due to the interaction of backstreaming suprathermal ions with a discontinuity, modifies the total pressure upstream of the bow shock showing a decrease within the FB׳s core and sheath regions. Magnetosheath plasma is accelerated towards the intersection of the FB׳s current sheet with the bow shock resulting in fast, sunward, flows as well as outward motion of the magnetopause. Ground-based magnetometers also show signatures of this magnetopause motion simultaneously across at least 7 h of magnetic local time, corresponding to a distance of 21.5RE transverse to the Sun–Earth line along the magnetopause. These observed global impacts of the FB are in agreement with previous simulations and in stark contrast to the known localised, smaller scale effects of Hot Flow Anomalies (HFAs).
Genestreti KJ, Fuselier SA, Goldstein J, et al., 2014, The location and rate of occurrence of near-Earth magnetotail reconnection as observed by Cluster and Geotail, JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS, Vol: 121, Pages: 98-109, ISSN: 1364-6826
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- Citations: 28
Phan TD, Drake JF, Shay MA, et al., 2014, Ion bulk heating in magnetic reconnection exhausts at Earth's magnetopause: Dependence on the inflow Alfven speed and magnetic shear angle, GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 7002-7010, ISSN: 0094-8276
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- Citations: 65
Archer MO, Turner DL, Eastwood JP, et al., 2014, The role of pressure gradients in driving sunward magnetosheath flows and magnetopause motion, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 8117-8125, ISSN: 2169-9380
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- Citations: 39
Oieroset M, Sundkvist D, Chaston CC, et al., 2014, Observations of plasma waves in the colliding jet region of amagnetic flux rope flanked by two active X lines at the subsolar magnetopause, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, ISSN: 2169-9380
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- Citations: 28
Jackman CM, Slavin JA, Kivelson MG, et al., 2014, Saturn's dynamic magnetotail: A comprehensive magnetic field and plasma survey of plasmoids and traveling compression regions and their role in global magnetospheric dynamics, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 5465-5494, ISSN: 2169-9380
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- Citations: 63
Selzer LA, Hnat B, Osman KT, et al., 2014, TEMPERATURE ANISOTROPY IN THE PRESENCE OF ULTRA LOW FREQUENCY WAVES IN THE TERRESTRIAL FORESHOCK, ASTROPHYSICAL JOURNAL LETTERS, Vol: 788, ISSN: 2041-8205
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- Citations: 5
Hietala H, Eastwood JP, Isavnin A, 2014, Sequentially released tilted flux ropes in the Earth's magnetotail, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 56, ISSN: 0741-3335
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- Citations: 17
Goldman MV, Newman DL, Lapenta G, et al., 2014, Cerenkov Emission of Quasiparallel Whistlers by Fast Electron Phase-Space Holes during Magnetic Reconnection, PHYSICAL REVIEW LETTERS, Vol: 112, ISSN: 0031-9007
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- Citations: 47
Eastwood JP, Phan TD, Oieroset M, et al., 2013, Influence of asymmetries and guide fields on the magnetic reconnection diffusion region in collisionless space plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 55, ISSN: 0741-3335
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- Citations: 42
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