Publications
225 results found
Krupar V, Maksimovic M, Kontar EP, et al., 2018, Interplanetary Type III Bursts and Electron Density Fluctuations in the Solar Wind, ASTROPHYSICAL JOURNAL, Vol: 857, ISSN: 0004-637X
Type III bursts are generated by fast electron beams originated from magnetic reconnection sites of solar flares. As propagation of radio waves in the interplanetary medium is strongly affected by random electron density fluctuations, type III bursts provide us with a unique diagnostic tool for solar wind remote plasma measurements. Here, we performed a statistical survey of 152 simple and isolated type III bursts observed by the twin-spacecraft Solar TErrestrial RElations Observatory mission. We investigated their time–frequency profiles in order to retrieve decay times as a function of frequency. Next, we performed Monte Carlo simulations to study the role of scattering due to random electron density fluctuations on time–frequency profiles of radio emissions generated in the interplanetary medium. For simplification, we assumed the presence of isotropic electron density fluctuations described by a power law with the Kolmogorov spectral index. Decay times obtained from observations and simulations were compared. We found that the characteristic exponential decay profile of type III bursts can be explained by the scattering of the fundamental component between the source and the observer despite restrictive assumptions included in the Monte Carlo simulation algorithm. Our results suggest that relative electron density fluctuations $\langle \delta {n}_{{\rm{e}}}\rangle /{n}_{{\rm{e}}}$ in the solar wind are 0.06–0.07 over wide range of heliospheric distances.
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.
Good SW, Forsyth RJ, Eastwood JP, et al., 2018, Correlation of ICME magnetic fields at radially aligned spacecraft, Solar Physics, Vol: 293, ISSN: 0038-0938
The magnetic field structures of two interplanetary coronal mass ejections (ICMEs), each observed by a pair of spacecraft close to radial alignment, have been analysed. The ICMEs were observed in situ by MESSENGER and STEREO-B in November 2010 and November 2011, while the spacecraft were separated by more than 0.6 AU in heliocentric distance, less than 4° in heliographic longitude, and less than 7° in heliographic latitude. Both ICMEs took approximately two days to travel between the spacecraft. The ICME magnetic field profiles observed at MESSENGER have been mapped to the heliocentric distance of STEREO-B and compared directly to the profiles observed by STEREO-B. Figures that result from this mapping allow for easy qualitative assessment of similarity in the profiles. Macroscale features in the profiles that varied on timescales of one hour, and which corresponded to the underlying flux rope structure of the ICMEs, were well correlated in the solar east–west and north–south directed components, with Pearson’s correlation coefficients of approximately 0.85 and 0.95, respectively; microscale features with timescales of one minute were uncorrelated. Overall correlation values in the profiles of one ICME were increased when an apparent change in the flux rope axis direction between the observing spacecraft was taken into account. The high degree of similarity seen in the magnetic field profiles may be interpreted in two ways. If the spacecraft sampled the same region of each ICME (i.e. if the spacecraft angular separations are neglected), the similarity indicates that there was little evolution in the underlying structure of the sampled region during propagation. Alternatively, if the spacecraft observed different, nearby regions within the ICMEs, it indicates that there was spatial homogeneity across those different regions. The field structure similarity observed in these ICMEs points to the value of placing in situ space weather monitors w
Genestreti KJ, Varsani A, Burch JL, et al., 2018, MMS observation of asymmetric reconnection supported by 3-D electron pressure divergence, Journal of Geophysical Research: Space Physics, Vol: 123, Pages: 1806-1821, ISSN: 2169-9380
We identify the electron diffusion region (EDR) of a guide field dayside reconnection site encountered by the Magnetospheric Multiscale (MMS) mission and estimate the terms in generalized Ohm's law that controlled energy conversion near the X-point. MMS crossed the moderate-shear (∼130°) magnetopause southward of the exact X-point. MMS likely entered the magnetopause far from the X-point, outside the EDR, as the size of the reconnection layer was less than but comparable to the magnetosheath proton gyroradius, and also as anisotropic gyrotropic "outflow" crescent electron distributions were observed. MMS then approached the X-point, where all four spacecraft simultaneously observed signatures of the EDR, for example, an intense out-of-plane electron current, moderate electron agyrotropy, intense electron anisotropy, nonideal electric fields, and nonideal energy conversion. We find that the electric field associated with the nonideal energy conversion is (a) well described by the sum of the electron inertial and pressure divergence terms in generalized Ohms law though (b) the pressure divergence term dominates the inertial term by roughly a factor of 5:1, (c) both the gyrotropic and agyrotropic pressure forces contribute to energy conversion at the X-point, and (d) both out-of-the-reconnection-plane gradients (∂/∂M) and in-plane (∂/∂L,N) in the pressure tensor contribute to energy conversion near the X-point. This indicates that this EDR had some electron-scale structure in the out-of-plane direction during the time when (and at the location where) the reconnection site was observed.
Kacem I, Jacquey C, Génot V, et al., 2018, Magnetic reconnection at a thin current sheet separating two interlaced flux tubes at the Earth's magnetopause, Journal of Geophysical Research: Space Physics, Vol: 123, Pages: 1779-1793, ISSN: 2169-9380
The occurrence of spatially and temporally variable reconnection at the Earth's magnetopause leads to the complex interaction of magnetic fields from the magnetosphere and magnetosheath. Flux transfer events (FTEs) constitute one such type of interaction. Their main characteristics are (1) an enhanced core magnetic field magnitude and (2) a bipolar magnetic field signature in the component normal to the magnetopause, reminiscent of a large-scale helicoidal flux tube magnetic configuration. However, other geometrical configurations which do not fit this classical picture have also been observed. Using high-resolution measurements from the Magnetospheric Multiscale mission, we investigate an event in the vicinity of the Earth's magnetopause on 7 November 2015. Despite signatures that, at first glance, appear consistent with a classic FTE, based on detailed geometrical and dynamical analyses as well as on topological signatures revealed by suprathermal electron properties, we demonstrate that this event is not consistent with a single, homogenous helicoidal structure. Our analysis rather suggests that it consists of the interaction of two separate sets of magnetic field lines with different connectivities. This complex three-dimensional interaction constructively conspires to produce signatures partially consistent with that of an FTE. We also show that, at the interface between the two sets of field lines, where the observed magnetic pileup occurs, a thin and strong current sheet forms with a large ion jet, which may be consistent with magnetic flux dissipation through magnetic reconnection in the interaction region.
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, Vol: 123, Pages: 1224-1241, ISSN: 2169-9380
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.
Zabori B, Hirn A, Eastwood J, et al., 2018, Space radiation and magnetic field environment specification for the Radcube space weather related CubeSat mission, ISSN: 0074-1795
To study space weather environment in space, as a first step, it is necessary to develop and establish an advanced, real-time monitoring system. Such a monitoring system may be able to provide scientific data on space radiation (electron and proton spectra, flux of heavier ions) and the status of the magnetosphere in order to gain the possibility for a reliable forecast capability. The expansion of the CubeSat/SmallSat industry will make it possible in the near future to launch orbital constellations with relevant, miniaturised instrumentation in order to study the space weather environment in near real-time. Thus the development of RADCUBE, a 3U CubeSat demonstration mission lead by a Hungarian company, called C3S LLC, for space weather monitoring purpose, has begun within the European Space Agency (ESA) CubeSat programme. As part of the development a new, combined, space weather monitoring instrument package (called RadMag) has been initiated at the Centre for Energy Research, Hungarian Academy of Sciences in the framework of ESA General Support Technology Programme (GSTP) in collaboration with Imperial College London and Astronika. The RadMag measurement capabilities were defined by reconstructing the expected space radiation and magnetic field environments for different orbit scenarios. The space radiation environment was analyzed considering the following parameters: flux of Galactic Cosmic Rays, trapped protons and electrons, solar particle events, corresponding Linear Energy Transfer (LET) spectra and Total Ionizing Dose (TID) levels. The expected magnetic field environment was modeled with the IGRF2015 + Tsyganenko-96 model both for quiet and stormy conditions. This paper addresses the results of these radiation and magnetic field environment reconstruction and calculations for the different possible orbital parameters of the RADCUBE mission in order to characterise the expected performance of the RadMag instrument during the RADCUBE mission. An overview of
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.
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.
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: 1944-8007
The Magnetospheric Multiscale mission is employed to examine intense Poynting flux directed along the background magnetic field toward Earth, which reaches amplitudes of nearly 2 mW/m2. The event is located within the plasma sheet but likely near the boundary at a geocentric distance of 9 RE in association with bulk flow signatures. The fluctuations have wavelengths perpendicular to the magnetic field of 124–264 km (compared to an ion gyroradius of 280 km), consistent with highly kinetic Alfvén waves. While the wave vector remains highly perpendicular to the magnetic field, there is substantial variation of the direction in the perpendicular plane. The field-aligned Poynting flux may be associated with kinetic Alfvén waves released along the separatrix by magnetotail reconnection and/or the radiation of waves excited by bursty bulk flow braking and may provide a means through which energy released by magnetic reconnection is transferred to the auroral region.
Eastwood J, Nakamura R, Turc L, et al., 2017, The scientific foundations of forecasting magnetospheric space weather, Space Science Reviews, Vol: 212, Pages: 1221-1252, ISSN: 1572-9672
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.
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.
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.
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
The solar wind provides an excellent opportunity to study the exhausts that form as a result of symmetric guide field reconnection, where spacecraft rapidly cross the exhausts far downstream of the X line. We study the statistical properties of solar wind exhausts through a superposed epoch analysis of 188 events observed at 1 AU using the Wind spacecraft. These events span a range of guide fields of 0 to 10 times the reconnecting magnetic field and inflow region plasma beta of 0.1 to 6.6. This analysis reveals that the out-of-plane magnetic field is enhanced within solar wind exhausts. Furthermore, the amount by which the plasma density and ion temperature increase from inflow region to exhaust region is found to be a function of the inflow region plasma beta and reconnection guide field, which explains the lack of these enhancements in a subset of previous observations. This dependence is consistent with the scaling of ion heating with inflow region Alfven speed, which is measured to be consistent with previous observations in the solar wind and at the magnetopause.
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
In Innocenti et al. (2015) we have observed and characterized for the first time Petschek-like switch-off slow shock/rotational discontinuity (SO-SS/RD) compound structures in a 2-D fully kinetic simulation of collisionless magnetic reconnection. Observing these structures in the solar wind or in the magnetotail would corroborate the possibility that Petschek exhausts develop in collisionless media as a result of single X point collisionless reconnection. Here we highlight their signatures in simulations with the aim of easing their identification in observations. The most notable signatures include a four-peaked ion current profile in the out-of-plane direction, associated ion distribution functions, increased electron and ion anisotropy downstream the SS, and increased electron agyrotropy downstream the RDs.
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
Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large-amplitude parallel electric fields (E||). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large-amplitude (~100 mV/m) E|| in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process.
Eastwood J, 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
Space weather describes the way in which the Sun, and conditions in space more generally, impact human activity and technology both in space and on the ground. It is now well understood that space weather represents a significant threat to infrastructure resilience, and is a source of risk that is wide‐ranging in its impact and the pathways by which this impact may occur. Although space weather is growing rapidly as a field, work rigorously assessing the overall economic cost of space weather appears to be in its infancy. Here, we provide an initial literature review to gather and assess the quality of any published assessments of space weather impacts and socioeconomic studies. Generally speaking, there is a good volume of scientific peer‐reviewed literature detailing the likelihood and statistics of different types of space weather phenomena. These phenomena all typically exhibit “power‐law” behavior in their severity. The literature on documented impacts is not as extensive, with many case studies, but few statistical studies. The literature on the economic impacts of space weather is rather sparse and not as well developed when compared to the other sections, most probably due to the somewhat limited data that are available from end‐users. The major risk is attached to power distribution systems and there is disagreement as to the severity of the technological footprint. This strongly controls the economic impact. Consequently, urgent work is required to better quantify the risk of future space weather events.
Fu HS, Vaivads A, Khotyaintsev YV, et al., 2017, Intermittent energy dissipation by turbulent reconnection, Geophysical Research Letters, Vol: 44, Pages: 37-43, ISSN: 1944-8007
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.
Kubicka M, Mostl C, Amerstorfer T, et al., 2016, Prediction of geomagnetic storm strength from inner heliospheric in situ observations, Astrophysical Journal, Vol: 833, ISSN: 1538-4357
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.
Stawarz JE, Eriksson S, Wilder FD, et al., 2016, Observations of turbulence in a Kelvin-Helmholtz event on September 8, 2015 by the Magnetospheric Multiscale Mission, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 11021-11034, ISSN: 2169-9380
Spatial and high-time-resolution properties of the velocities,magnetic eld, and 3D electric eld within plasma turbulence are examined observationally using data from the Magnetospheric Multiscale Mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a rst look at the properties of turbulence in the KHI. For the rst time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra ex-hibit power law behavior with changes in slope near the ion gyrofrequency and lower-hybrid frequency. The work provides the rst observational evi-dence for turbulent intermittency and anisotropy consistent with quasi-two-dimensional turbulence in association with the KHI. The behavior of kinetic scale intermittency is found to have di erences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics inthe KHI.
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: 1079-7114
Observations made using the Wind spacecraft of Hall magnetic fields in solar wind reconnection exhausts are presented. These observations are consistent with the generation of Hall fields by a narrow ion inertial scale current layer near the separatrix, which is confirmed with an appropriately scaled particle-in-cell simulation that shows excellent agreement with observations. The Hall fields are observed thousands of ion inertial lengths downstream from the reconnection X line, indicating that narrow regions of kinetic dynamics can persist extremely far downstream.
Vaivads A, Retino A, Soucek J, et al., 2016, Turbulence Heating ObserveR – satellite mission proposal, Journal of Plasma Physics, Vol: 82, ISSN: 1469-7807
The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth’s magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space – magnetosheath, shock, foreshock and pristine solar wind – featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the ‘Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)’. THOR has been selected by European Space Agency (ESA) for the study phase.
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
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 (di) 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 di in width, extend at least 9 di 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.
Mejnertsen L, Eastwood JP, Chittenden J, et al., 2016, Global MHD Simulations of Neptune's Magnetosphere, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 7497-7513, ISSN: 2169-9380
A global magnetohydrodynamic (MHD) simulation has been performed in order to investigate the outer boundaries of Neptune's magnetosphere at the time of Voyager 2's flyby in 1989 and to better understand the dynamics of magnetospheres formed by highly inclined planetary dipoles. Using the MHD code Gorgon, we have implemented a precessing dipole to mimic Neptune's tilted magnetic field and rotation axes. By using the solar wind parameters measured by Voyager 2, the simulation is verified by finding good agreement with Voyager 2 magnetometer observations. Overall, there is a large-scale reconfiguration of magnetic topology and plasma distribution. During the “pole-on” magnetospheric configuration, there only exists one tail current sheet, contained between a rarefied lobe region which extends outward from the dayside cusp, and a lobe region attached to the nightside cusp. It is found that the tail current always closes to the magnetopause current system, rather than closing in on itself, as suggested by other models. The bow shock position and shape is found to be dependent on Neptune's daily rotation, with maximum standoff being during the pole-on case. Reconnection is found on the magnetopause but is highly modulated by the interplanetary magnetic field (IMF) and time of day, turning “off” and “on” when the magnetic shear between the IMF and planetary fields is large enough. The simulation shows that the most likely location for reconnection to occur during Voyager 2's flyby was far from the spacecraft trajectory, which may explain the relative lack of associated signatures in the observations.
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
The systematic monitoring of the solar wind in high-cadence and high-resolution heliospheric images taken by the Solar-Terrestrial Relation Observatory (STEREO) spacecraft permits the study of the spatial and temporal evolution of variable solar wind flows from the Sun out to 1 AU, and beyond. As part of the EU Framework 7 (FP7) Heliospheric Cataloguing, Analysis and Techniques Service (HELCATS) project, we have generated a catalog listing the properties of 190 corotating structures well-observed in images taken by the Heliospheric Imager (HI) instruments onboard STEREO-A (ST-A). Based on this catalog, we present here one of very few long-term analyses of solar wind structures advected by the background solar wind. We concentrate on the subset of plasma density structures clearly identified inside corotating structures. This analysis confirms that most of the corotating density structures detected by the heliospheric imagers comprises a series of density inhomogeneities advected by the slow solar wind that eventually become entrained by stream interaction regions. We have derived the spatial-temporal evolution of each of these corotating density structures by using a well-established fitting technique. The mean radial propagation speed of the corotating structures is found to be (Formula presented.). Such a low mean value corresponds to the terminal speed of the slow solar wind rather than the speed of stream interfaces, which is typically intermediate between the slow and fast solar wind speeds ((Formula presented.)). Using our fitting technique, we predicted the arrival time of each corotating density structure at different probes in the inner heliosphere. We find that our derived speeds are systematically lower by (Formula presented.) than those measured in situ at the predicted impact times. Moreover, for cases when a stream interaction region is clearly detected in situ at the estimated impact time, we find that our derived speeds are lower than the speed of th
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: 1079-7114
We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E_{∥}) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E_{∥} events near the electron diffusion region have amplitudes on the order of 100 mV/m, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E_{∥} events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E_{∥} events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.
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
We present a concept for a small mission to the Sun–Earth Lagrangian L5 point for innovative solar, heliospheric and space weather science. The proposed INvestigation of Solar-Terrestrial Activity aNd Transients (INSTANT) mission is designed to identify how solar coronal magnetic fields drive eruptions, mass transport and particle acceleration that impact the Earth and the heliosphere. INSTANT is the first mission designed to (1) obtain measurements of coronal magnetic fields from space and (2) determine coronal mass ejection (CME) kinematics with unparalleled accuracy. Thanks to innovative instrumentation at a vantage point that provides the most suitable perspective view of the Sun–Earth system, INSTANT would uniquely track the whole chain of fundamental processes driving space weather at Earth. We present the science requirements, payload and mission profile that fulfill ambitious science objectives within small mission programmatic boundary conditions.
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
We report Magnetospheric Multiscale observations of macroscopic and electron-scale current layers in asymmetric reconnection. By intercomparing plasma, magnetic, and electric field data at multiple crossings of a reconnecting magnetopause on 22 October 2015, when the average interspacecraft separation was ~10km, we demonstrate that the ion and electron moments are sufficiently accurate to provide reliable current density measurements at 30ms cadence. These measurements, which resolve current layers narrower than the interspacecraft separation, reveal electron-scale filamentary Hall currents and electron vorticity within the reconnection exhaust far downstream of the X line and even in the magnetosheath. Slightly downstream of the X line, intense (up to 3μA/m2) electron currents, a super-Alfvénic outflowing electron jet, and nongyrotropic crescent shape electron distributions were observed deep inside the ion-scale magnetopause current sheet and embedded in the ion diffusion region. These characteristics are similar to those attributed to the electron dissipation/diffusion region around the X line.
Øieroset 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
We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's 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.
Burch J, Torbert RB, Phan TD, et al., 2016, Electron-scale measurements of magnetic reconnection in space, Science, Vol: 352, ISSN: 1095-9203
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.
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