128 results found
Akhavan-Tafti M, Slavin JA, Le G, et al., 2018, MMS Examination of FTEs at the Earth's Subsolar Magnetopause, Journal of Geophysical Research: Space Physics, ISSN: 2169-9380
©2018. The Authors. Determining the magnetic field structure, electric currents, and plasma distributions within flux transfer event (FTE)-type flux ropes is critical to the understanding of their origin, evolution, and dynamics. Here the Magnetospheric Multiscale mission's high-resolution magnetic field and plasma measurements are used to identify FTEs in the vicinity of the subsolar magnetopause. The constant-α flux rope model is used to identify quasi-force free flux ropes and to infer the size, the core magnetic field strength, the magnetic flux content, and the spacecraft trajectories through these structures. Our statistical analysis determines a mean diameter of 1,700 ± 400 km (~30 ± 9 d i ) and an average magnetic flux content of 100 ± 30 kWb for the quasi-force free FTEs at the Earth's subsolar magnetopause which are smaller than values reported by Cluster at high latitudes. These observed nonlinear size and magnetic flux content distributions of FTEs appear consistent with the plasmoid instability theory, which relies on the merging of neighboring, small-scale FTEs to generate larger structures. The ratio of the perpendicular to parallel components of current density, R J , indicates that our FTEs are magnetically force-free, defined as R J < 1, in their core regions ( < 0.6 R flux rope ). Plasma density is shown to be larger in smaller, newly formed FTEs and dropping with increasing FTE size. It is also shown that parallel ion velocity dominates inside FTEs with largest plasma density. Field-aligned flow facilitates the evacuation of plasma inside newly formed FTEs, while their core magnetic field strengthens with increasing FTE size.
Good SW, Forsyth RJ, Eastwood JP, et al., 2018, Correlation of ICME Magnetic Fields at Radially Aligned Spacecraft, Solar Physics, ISSN: 0038-0938
Mejnertsen L, Eastwood JP, Hietala H, et al., 2018, 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
Eastwood JP, Biffis E, Hapgood MA, et al., 2017, The Economic Impact of Space Weather: Where Do We Stand?, RISK ANALYSIS, Vol: 37, Pages: 206-218, ISSN: 0272-4332
Eastwood JP, Nakamura R, Turc L, et al., 2017, The Scientific Foundations of Forecasting Magnetospheric Space Weather, Space Science Reviews, Vol: 212, Pages: 1221-1252, ISSN: 0038-6308
© 2017, The Author(s). The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth’s magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.
Ergun RE, Chen L-J, Wilder FD, et al., 2017, Drift waves, intense parallel electric fields, and turbulence associated with asymmetric magnetic reconnection at the magnetopause, GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 2978-2986, ISSN: 0094-8276
Farrugia CJ, Lugaz N, Alm L, et al., 2017, MMS Observations of Reconnection at Dayside Magnetopause Crossings During Transitions of the Solar Wind to Sub-Alfvénic Flow, Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 9934-9951, ISSN: 2169-9380
We present MMS observations during two dayside magnetopause crossings under hithertounexamined conditions: (i) when the bow shock is weakening and the solar wind transitioning tosub-Alfvénic flow and (ii) when it is reforming. Interplanetary conditions consist of a magnetic cloud with (i)a strongB(∼20 nT) pointing south and (ii) a density profile with episodic decreases to values of∼0.3 cm−3followed by moderate recovery. During the crossings the magnetosheath magnetic field is stronger thanthe magnetosphere field by a factor of∼2.2. As a result, during the outbound crossing through the iondiffusion region, MMS observed an inversion of the relative positions of the X and stagnation (S) lines fromthat typically the case: the S line was closer to the magnetosheath side. The S line appears in the form of aslow expansion fan near which most of the energy dissipation is taking place. While in the magnetospherebetween the crossings, MMS observed strong field and flow perturbations, which we argue to be due tokinetic Alfvén waves. During the reconnection interval, whistler mode waves generated by an electrontemperature anisotropy (Te⟂>Te∥) were observed. Another aim of the paper is to distinguish bowshock-induced field and flow perturbations from reconnection-related signatures. The high-resolutionMMS data together with 2-D hybrid simulations of bow shock dynamics helped us to distinguish betweenthe two sources. We show examples of bow shock-related effects (such as heating) and reconnectioneffects such as accelerated flows satisfying the Walén relation.
Fu HS, Vaivads A, Khotyaintsev YV, et al., 2017, Intermittent energy dissipation by turbulent reconnection, Geophysical Research Letters, Vol: 44, Pages: 37-43, ISSN: 0094-8276
©2016. American Geophysical Union. All Rights Reserved. Magnetic reconnection—the process responsible for many explosive phenomena in both nature and laboratory—is efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the “diffusion region” at the sub-ion scale. Here we report such a measurement by Cluster—four spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, E′ ⋅ j, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.
Innocenti ME, Cazzola E, Mistry R, et al., 2017, Switch-off slow shock/rotational discontinuity structures in collisionless magnetic reconnection: What to look for in satellite observations, GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 3447-3455, ISSN: 0094-8276
Mistry R, Eastwood JP, Phan TD, et al., 2017, Statistical properties of solar wind reconnection exhausts, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 5895-5909, ISSN: 2169-9380
Moestl C, Isavnin A, Boakes PD, et al., 2017, Modeling observations of solar coronal mass ejections with heliospheric imagers verified with the Heliophysics System Observatory, Space Weather-the International Journal of Research and Applications, Vol: 15, Pages: 955-970, ISSN: 1539-4956
We present an advance toward accurately predicting the arrivals of coronal mass ejections (CMEs) at the terrestrial planets, including Earth. For the first time, we are able to assess a CME prediction model using data over two thirds of a solar cycle of observations with the Heliophysics System Observatory. We validate modeling results of 1337 CMEs observed with the Solar Terrestrial Relations Observatory (STEREO) heliospheric imagers (HI) (science data) from 8 years of observations by five in situ observing spacecraft. We use the self-similar expansion model for CME fronts assuming 60° longitudinal width, constant speed, and constant propagation direction. With these assumptions we find that 23%–35% of all CMEs that were predicted to hit a certain spacecraft lead to clear in situ signatures, so that for one correct prediction, two to three false alarms would have been issued. In addition, we find that the prediction accuracy does not degrade with the HI longitudinal separation from Earth. Predicted arrival times are on average within 2.6 ± 16.6 h difference of the in situ arrival time, similar to analytical and numerical modeling, and a true skill statistic of 0.21. We also discuss various factors that may improve the accuracy of space weather forecasting using wide-angle heliospheric imager observations. These results form a first-order approximated baseline of the prediction accuracy that is possible with HI and other methods used for data by an operational space weather mission at the Sun-Earth L5 point.
Stawarz JE, Eastwood JP, Varsani A, et al., 2017, Magnetospheric Multiscale analysis of intense field-aligned Poynting flux near the Earth's plasma sheet boundary, GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 7106-7113, ISSN: 0094-8276
Øieroset M, Phan TD, Shay MA, et al., 2017, THEMIS multispacecraft observations of a reconnecting magnetosheath current sheet with symmetric boundary conditions and a large guide field, Geophysical Research Letters, Vol: 44, Pages: 7598-7606, ISSN: 0094-8276
We report three spacecraft observations of a reconnecting magnetosheath current sheet with a guide field of unity, with THEMIS D (THD) and THEMIS E (THE)/THEMIS A (THA) observing oppositely directed reconnection exhausts, indicating the presence of an X line between the spacecraft. The near-constant convective speed of the magnetosheath current sheet allowed the direct translation of the observed time series into spatial profiles. THD observed asymmetries in the plasma density and temperature profiles across the exhaust, characteristics of symmetric reconnection with a guide field. The exhausts at THE and THA, on the other hand, were not the expected mirror image of the THD exhaust in terms of the plasma and field profiles. They consisted of a main outflow at the center of the current sheet, flanked by oppositely directed flows at the two edges of the current sheet, suggesting the presence of a second X line, whose outflow wraps around the outflow from the first X line.
Arridge CS, Eastwood JP, Jackman CM, et al., 2016, Cassini in situ observations of long-duration magnetic reconnection in Saturn's magnetotail, NATURE PHYSICS, Vol: 12, Pages: 268-271, ISSN: 1745-2473
Burch JL, Torbert RB, Phan TD, et al., 2016, Electron-scale measurements of magnetic reconnection in space, SCIENCE, Vol: 352, ISSN: 0036-8075
Eastwood JP, Phan TD, 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: 0094-8276
Ergun RE, Goodrich KA, Wilder FD, et al., 2016, Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection, PHYSICAL REVIEW LETTERS, Vol: 116, ISSN: 0031-9007
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
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-Alfvenic flow, GEOPHYSICAL RESEARCH LETTERS, Vol: 43, Pages: 6070-6077, ISSN: 0094-8276
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
Kubicka M, Möstl C, Amerstorfer T, et al., 2016, PREDICTION of GEOMAGNETIC STORM STRENGTH from INNER HELIOSPHERIC in SITU OBSERVATIONS, Astrophysical Journal, Vol: 833, ISSN: 0004-637X
© 2016. The American Astronomical Society. All rights reserved. Prediction of the effects of coronal mass ejections (CMEs) on Earth strongly depends on knowledge of the interplanetary magnetic field southward component, B z . Predicting the strength and duration of B z inside a CME with sufficient accuracy is currently impossible, forming the so-called B z problem. Here, we provide a proof-of-concept of a new method for predicting the CME arrival time, speed, B z , and resulting disturbance storm time (Dst) index on Earth based only on magnetic field data, measured in situ in the inner heliosphere ( < 1 au). On 2012 June 12-16, three approximately Earthward-directed and interacting CMEs were observed by the Solar Terrestrial Relations Observatory imagers and Venus Express (VEX) in situ at 0.72 au, 6° away from the Sun-Earth line. The CME kinematics are calculated using the drag-based and WSA-Enlil models, constrained by the arrival time at VEX, resulting in the CME arrival time and speed on Earth. The CME magnetic field strength is scaled with a power law from VEX to Wind. Our investigation shows promising results for the Dst forecast (predicted: -96 and -114 nT (from 2 Dst models); observed: -71 nT), for the arrival speed (predicted: 531 ±23 km s -1 ; observed: 488 ±30 km s -1 ), and for the timing (6 ±1 hr after the actual arrival time). The prediction lead time is 21 hr. The method may be applied to vector magnetic field data from a spacecraft at an artificial Lagrange point between the Sun and Earth or to data taken by any spacecraft temporarily crossing the Sun-Earth line.
Lavraud B, Liu Y, Segura K, et al., 2016, A small mission concept to the Sun-Earth Lagrangian L5 point for innovative solar, heliospheric and space weather science, JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS, Vol: 146, Pages: 171-185, ISSN: 1364-6826
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: 0094-8276
Mistry R, Eastwood JP, Haggerty CC, et al., 2016, Observations of Hall Reconnection Physics Far Downstream of the X Line, PHYSICAL REVIEW LETTERS, Vol: 117, ISSN: 0031-9007
Oieroset M, Phan TD, Haggerty C, et al., 2016, MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause, GEOPHYSICAL RESEARCH LETTERS, Vol: 43, Pages: 5536-5544, ISSN: 0094-8276
Phan TD, Eastwood JP, Cassak PA, et al., 2016, MMS observations of electron-scale filamentary currents in the reconnection exhaust and near the X line, GEOPHYSICAL RESEARCH LETTERS, Vol: 43, Pages: 6060-6069, ISSN: 0094-8276
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.
Phan TD, Shay MA, Haggerty CC, et al., 2016, Ion Larmor radius effects near a reconnection X line at the magnetopause: THEMIS observations and simulation comparison, Geophysical Research Letters, Vol: 43, Pages: 8844-8852, ISSN: 0094-8276
©2016. American Geophysical Union. All Rights Reserved. We report a Time History of Events and Macroscale Interactions during Substorms (THEMIS-D) spacecraft crossing of a magnetopause reconnection exhaust ~9 ion skin depths (d i ) downstream of an X line. The crossing was characterized by ion jetting at speeds substantially below the predicted reconnection outflow speed. In the magnetospheric inflow region THEMIS detected (a) penetration of magnetosheath ions and the resulting flows perpendicular to the reconnection plane, (b) ion outflow extending into the magnetosphere, and (c) enhanced electron parallel temperature. Comparison with a simulation suggests that these signatures are associated with the gyration of magnetosheath ions onto magnetospheric field lines due to the shift of the flow stagnation point toward the low-density magnetosphere. Our observations indicate that these effects, ~2–3 d i in width, extend at least 9 d i downstream of the X line. The detection of these signatures could indicate large-scale proximity of the X line but do not imply that the spacecraft was upstream of the electron diffusion region.
Plotnikov I, Rouillard AP, Davies JA, et al., 2016, Long-Term Tracking of Corotating Density Structures Using Heliospheric Imaging, SOLAR PHYSICS, Vol: 291, Pages: 1853-1875, ISSN: 0038-0938
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