Publications
225 results found
Waters C, Eastwood J, Fargette N, et al., 2024, A machine learning approach to structure and energy in magnetic reconnection
<jats:p>Magnetic reconnection is a fundamentally important process in space plasmas due to the release and repartition of the magnetic energy stored within the reconnecting field. As this energy transfer significantly impacts magnetospheric dynamics, understanding the partition of this energy and how this varies across the reconnection site can provide further insight into other magnetospheric processes. Although in situ spacecraft data provide direct measurements of relevant plasma properties, it can be difficult to establish the location of spacecraft relative to the reconnection site. This frustrates efforts to evaluate the way in which energy fluxes change with distance from the central reconnection X-line. Under certain circumstances, reconstruction techniques can be used to estimate the spacecraft trajectory through individual events, but these may rely on simplifying assumptions limiting their use.This motivates new approaches to determining where a spacecraft is relative to the reconnection structure. By utilising forefront machine learning techniques, we can more accurately study individual regions associated with the reconnection process and thus understand how they individually contribute to repartitioning the overall energy budget. In this context, we present these new applications of machine learning techniques to identify the regions in both simulation and spacecraft data.Firstly, we present the results of a robust method which utilises k-means clustering to identify different regions encountered within the overall reconnection X-line structure. This uses plasma fluid and field variables output by a 2.5-D PIC simulation with a geometry comparable to that of reconnection in Earth&#8217;s magnetotail. We then translate this model for use in spacecraft data by implementing an approach based on a recurrent neural network to account for the temporal context of the observations. We demonstrate the use of this model on MMS observations of reconn
Klein KG, Spence H, Alexandrova O, et al., 2023, HelioSwarm: a multipoint, multiscale mission to characterize turbulence, Space Science Reviews, Vol: 219, ISSN: 0038-6308
HelioSwarm (HS) is a NASA Medium-Class Explorer mission of the Heliophysics Division designed to explore the dynamic three-dimensional mechanisms controlling the physics of plasma turbulence, a ubiquitous process occurring in the heliosphere and in plasmas throughout the universe. This will be accomplished by making simultaneous measurements at nine spacecraft with separations spanning magnetohydrodynamic and sub-ion spatial scales in a variety of near-Earth plasmas. In this paper, we describe the scientific background for the HS investigation, the mission goals and objectives, the observatory reference trajectory and instrumentation implementation before the start of Phase B. Through multipoint, multiscale measurements, HS promises to reveal how energy is transferred across scales and boundaries in plasmas throughout the universe.
Hwang K-J, Nakamura R, Eastwood JP, et al., 2023, Cross-scale processes of magnetic reconnection, Space Science Reviews, Vol: 219, ISSN: 0038-6308
Various physical processes in association with magnetic reconnection occur over multiple scales from the microscopic to macroscopic scale lengths. This paper reviews multi-scale and cross-scale aspects of magnetic reconnection revealed in the near-Earth space beyond the general global-scale features and magnetospheric circulation organized by the Dungey Cycle. Significant and novel advancements recently reported, in particular, since the launch of the Magnetospheric Multi-scale mission (MMS), are highlighted being categorized into different locations with different magnetic topologies. These potentially paradigm-shifting findings include shock and foreshock transient driven reconnection, magnetosheath turbulent reconnection, flow shear driven reconnection, multiple X-line structures generated in the dayside/flankside/nightside magnetospheric current sheets, development and evolution of reconnection-driven structures such as flux transfer events, flux ropes, and dipolarization fronts, and their interactions with ambient plasmas. The paper emphasizes key aspects of kinetic processes leading to multi-scale structures and bringing large-scale impacts of magnetic reconnection as discovered in the geospace environment. These key features can be relevant and applicable to understanding other heliospheric and astrophysical systems.
Adhikari S, Shay M, Parashar T, et al., 2023, Effect of a guide field on the turbulence like properties of magnetic reconnection, Physics of Plasmas, Vol: 30, Pages: 1-14, ISSN: 1070-664X
The effect of an external guide field on the turbulence-like properties of magneticreconnection is studied using five different 2.5D kinetic particle-in-cell (PIC) simulations. The magnetic energy spectrum is found to exhibit a slope of approximately−5/3 in the inertial range, independent of the guide field. On the contrary, theelectric field spectrum, in the inertial range steepens more with the guide field andapproaches a slope of −5/3. In addition, spectral analysis of the different terms ofthe generalized Ohm’s law is performed and found to be consistent with PIC simulations of turbulence and MMS observations. Finally, the guide field effect on theenergy transfer behavior is examined using von-K´arm´an Howarth (vKH) equationbased on incompressible Hall-MHD. The general characteristics of the vKH equationwith constant rate of energy transfer in the inertial range, is consistent in all the simulations. This suggests that the qualitative behavior of energy spectrum, and energytransfer in reconnection is similar to that of turbulence, indicating that reconnectionfundamentally involves an energy cascade.
Khabarova O, Balasis G, Bučík R, et al., 2023, Editorial: Reviews in space physics, Frontiers in Astronomy and Space Sciences, Vol: 10, Pages: 1-3, ISSN: 2296-987X
de Moortel I, Eastwood J, Bridges J, et al., 2023, Future UK solar system science, Astronomy and Geophysics, Vol: 64, Pages: 3.34-3.38, ISSN: 0035-8738
Fargette N, Lavraud B, Rouillard AP, et al., 2023, Clustering of magnetic reconnection exhausts in the solar wind: An automated detection study, Astronomy and Astrophysics: a European journal, Vol: 674, Pages: 1-15, ISSN: 0004-6361
Context. Magnetic reconnection is a fundamental process in astrophysical plasmas that enables the dissipation of magnetic energy at kinetic scales. Detecting this process in situ is therefore key to furthering our understanding of energy conversion in space plasmas. However, reconnection jets typically scale from seconds to minutes in situ, and as such, finding them in the decades of data provided by solar wind missions since the beginning of the space era is an onerous task.Aims. In this work, we present a new approach for automatically identifying reconnection exhausts in situ in the solar wind. We apply the algorithm to Solar Orbiter data obtained while the spacecraft was positioned at between 0.6 and 0.8 AU and perform a statistical study on the jets we detect.Methods. The method for automatic detection is inspired by the visual identification process and strongly relies on the Walén relation. It is enhanced through the use of Bayesian inference and physical considerations to detect reconnection jets with a consistent approach.Results. Applying the detection algorithm to one month of Solar Orbiter data near 0.7 AU, we find an occurrence rate of seven jets per day, which is significantly higher than in previous studies performed at 1 AU. We show that they tend to cluster in the solar wind and are less likely to occur in the tenuous solar wind (< 10 cm−3 near 0.7 AU). We discuss why the source and the degree of Alfvénicity of the solar wind might have an impact on magnetic reconnection occurrence.Conclusions. By providing a tool to quickly identify potential magnetic reconnection exhausts in situ, we pave the way for broader statistical studies on magnetic reconnection in diverse plasma environments.
Desai R, Eastwood J, Glauert S, et al., 2023, Resolving Multiscale Magnetospheric and Radiation Belt Dynamics using Global MHD, Test Particle and Fokker Planck Simulations
<jats:p>The global magnetosphere represents an intricate and multi-scale system with dynamics occurring across scales ranging from metres to miles and milli-seconds to days. This represents a formidable challenge to understand, and differing plasma theories are typically applied to model the large-scale electromagnetic fields and the dynamics of the Van Allen radiation belts. This discretisation of plasma regimes, however, breaks down during extreme conditions when the magnetosphere becomes highly distorted and energetic particle dynamics vary rapidly across sub-drift timescales. To self-consistently model both short and long timescales, we combine global MHD and particle simulations with Fokker-Planck simulations to demonstrate how this presents a realistic and also necessary method to capture magnetospheric and radiation belt dynamics during severe geomagnetic storms. The global MHD simulations capture the large-scale modulations to the global magnetic and electric fields and the integrated particle simulations reveal intense acceleration processes during the compression phase and subsequent injections through the magnetotail. At relativistic energies, loss processes at low L shells are limited and the Fokker-Planck model reveals how newly accelerated radiation belt distributions evolve and persist over extended time periods. Modelling this flow of energy from the solar wind through to ring current and radiation belt populations, across both short and long time-scales, requires detailed observational constraints and we discuss how upcoming space missions will help us to holistically constrain energy transfers through our puzzling magnetosphere.&#160;</jats:p>
Kelly H, Archer M, Eggington J, et al., 2023, Formation and identification of Kelvin-Helmholtz generated vortices at Earths magnetopause: Insight from adapting hydrodynamic techniques for MHD
<jats:p>The Kelvin-Helmholtz Instability (KHI) plays a significant role in the viscous-like mass, momentum, and energy transfer from the solar wind into the magnetosphere through both vortical and wave dynamics. To confidently study and compare the effects of these dynamics, we must formally define a vortex. Previously, a definition did not exist for the magnetohydrodynamic (MHD) regime. Consequently, we have developed a novel vortex definition (the `&#955;MHD definition&#8217;) for MHD flows. This is based on adapting well-used hydrodynamic techniques (the &#955;2 family of methods) that defines a vortex as a local minimum in an adapted pressure field. We derive the MHD suitable adapted pressure field from the ideal MHD Cauchy-Momentum equation, and find that it is composed of four components. The first three components represent the hydrodynamic properties of rotational momentum flow, density inhomogeneity, and fluid compressibility respectively. The final component makes the &#955;MHD definition unique from hydrodynamics as it represents the rotational component of the J&#215;B Lorentz force which is found using a Helmholtz decomposition. We use the Gorgon global 3-Dimensional MHD code to validate the &#955;MHD vortex definition within a northward IMF simulation run exhibiting KHI-driven waves at the magnetopause flanks. Comparison of &#955;MHD with existing hydrodynamic definitions shows good correlations and skill scores, particularly with the more advanced methods. Our analysis also reveals that the rotational momentum flow term dominates at the magnetopause. The other components provide typically small corrections to this. We have found that at the magnetopause, compressibility generally acts in opposition to the existence of a pressure minimum and thus a vortex. Alternatively, inhomogeneity and the rotational component of the Lorentz force generally act to support the pressure minimum. We explore
Dandouras I, Taylor MGGT, De Keyser J, et al., 2023, Space plasma physics science opportunities for the lunar orbital platform - Gateway, Frontiers in Astronomy and Space Sciences, Vol: 10, Pages: 1-30, ISSN: 2296-987X
The Lunar Orbital Platform - Gateway (LOP - Gateway, or simply Gateway) is a crewed platform that will be assembled and operated in the vicinity of the Moon by NASA and international partner organizations, including ESA, starting from the mid-2020s. It will offer new opportunities for fundamental and applied scientific research. The Moon is a unique location to study the deep space plasma environment. Moreover, the lunar surface and the surface-bounded exosphere are interacting with this environment, constituting a complex multi-scale interacting system. This paper examines the opportunities provided by externally mounted payloads on the Gateway in the field of space plasma physics, heliophysics and space weather, and also examines the impact of the space environment on an inhabited platform in the vicinity of the Moon. It then presents the conceptual design of a model payload, required to perform these space plasma measurements and observations. It results that the Gateway is very well-suited for space plasma physics research. It allows a series of scientific objectives with a multi-disciplinary dimension to be addressed.
Krasnoselskikh V, Tsurutani BT, Dudok de Wit T, et al., 2023, ICARUS: in-situ studies of the solar corona beyond Parker Solar Probe and Solar Orbiter, Experimental Astronomy, Vol: 54, Pages: 277-315, ISSN: 0922-6435
The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA “Voyage 2050” Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap, these science goals address Theme 2: “How does the Solar System work?” by investigating basic processes occurring “From the Sun to the edge of the Solar System”. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosph
Maffei S, Eggington JWB, Livermore PW, et al., 2023, Climatological predictions of the auroral zone locations driven by moderate and severe space weather events, Scientific Reports, Vol: 13, Pages: 1-11, ISSN: 2045-2322
Auroral zones are regions where, in an average sense, aurorae due to solar activity are most likely spotted. Their shape and, similarly, the geographical locations most vulnerable to extreme space weather events (which we term ‘danger zones’) are modulated by Earth’s time-dependent internal magnetic field whose structure changes on yearly to decadal timescales. Strategies for mitigating ground-based space weather impacts over the next few decades can benefit from accurate forecasts of this evolution. Existing auroral zone forecasts use simplified assumptions of geomagnetic field variations. By harnessing the capability of modern geomagnetic field forecasts based on the dynamics of Earth’s core we estimate the evolution of the auroral zones and of the danger zones over the next 50 years. Our results predict that space-weather related risk will not change significantly in Europe, Australia and New Zealand. Mid-to-high latitude cities such as Edinburgh, Copenhagen and Dunedin will remain in high-risk regions. However, northward change of the auroral and danger zones over North America will likely cause urban centres such as Edmonton and Labrador City to be exposed by 2070 to the potential impact of severe solar activity.
Eckersley S, Rowe S, Hill W, et al., 2023, An ESA Nanosatellite Constellation to Monitor Space Weather Effects, ISSN: 0074-1795
Major space weather events have the potential to cause significant damage and disruption to critical terrestrial and space-based infrastructure, including radio communication networks, Global Navigation Satellite Systems (GNSS) and the electricity grid. The continuous monitoring of space weather is therefore crucial for providing advanced warning of potentially destructive events. The European Space Agency (ESA) is in the process of developing the Enhanced Space Weather Monitoring System, which will utilise spacecraft to monitor space weather on and away from the Sun-Earth line (e.g., the ESA Vigil mission). The Distributed Space Weather Sensor System (D3S) will form part of this Enhanced Space Weather Monitoring System and focus on making measurements in the vicinity of the Earth. In early 2021, SSTL was selected to lead an ESA-funded Phase 0/A study titled “SSA P3-SWE-LIII Nanosatellites for D3S”. The aim of the study was to establish the role that nanosatellites can play as part of the D3S space weather monitoring system. Nanosatellite technologies have seen significant performance and capability improvements in recent years, and this was one of the reasons that nanosatellites were of particular interest for this study, along with the benefit of their small size and lower costs. The objective of the Phase 0 study was to analyse the space weather measurement requirements for the mission and identify potential space weather instruments that could be accommodated on a nanosatellite mission. A trade-off of a range of different mission architecture concepts was conducted, and the two most promising concepts were selected for more detailed analysis in the latter half of the Phase 0 study. At the end of Phase 0, ESA selected a concept comprising 6x 16U SSTL CubeSats in a 500-600km Sun-Synchronous Orbit to take forward into Phase A for further definition. The Phase A study focussed on the more detailed design of a precursor demonstration mission comprised of
Koehn G, Desai R, Davies E, et al., 2022, Successive interacting coronal mass ejections: How to create a perfect storm?, The Astrophysical Journal: an international review of astronomy and astronomical physics, Vol: 941, ISSN: 0004-637X
Coronal mass ejections (CMEs) are the largest type of eruptions on the Sun and the main driver of severe space weather at the Earth. In this study, we implement a force-free spheromak CME description within 3D magnetohydrodynamic simulations to parametrically evaluate successive interacting CMEs within a representative heliosphere. We explore CME–CME interactions for a range of orientations, launch time variations, and CME handedness and quantify their geo-effectiveness via the primary solar wind variables and empirical measures of the disturbance storm time index and subsolar magnetopause standoff distance. We show how the interaction of two moderate CMEs between the Sun and the Earth can translate into extreme conditions at the Earth and how CME–CME interactions at different radial distances can maximize different solar wind variables that induce different geophysical impacts. In particular, we demonstrate how the orientation and handedness of a given CME can have a significant impact on the conservation and loss of magnetic flux, and consequently Bz, due to magnetic reconnection with the interplanetary magnetic field. This study thus implicates the identification of CME chirality in the solar corona as an early diagnostic for forecasting geomagnetic storms involving multiple CMEs.
Retino A, Khotyaintsev Y, Le Contel O, et al., 2022, Particle energization in space plasmas: towards a multi-point, multi-scale plasma observatory, Experimental Astronomy: an international journal on astronomical instrumentation and data analysis, Vol: 54, Pages: 427-471, ISSN: 0922-6435
This White Paper outlines the importance of addressing the fundamental science theme “How are charged particles energized in space plasmas” through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field.
Eggington J, Coxon J, Shore R, et al., 2022, Response timescales of the magnetotail current sheet during a geomagnetic storm: global MHD simulations, Frontiers in Astronomy and Space Sciences, Vol: 9, Pages: 1-17, ISSN: 2296-987X
The response of the Earth’s magnetotail current sheet to the external solar wind driver is highly time-dependent and asymmetric. For example, the current sheet twists in response to variations in the By component of the interplanetary magnetic field (IMF), and is hinged by the dipole tilt. Understanding the timescales over which these asymmetries manifest is of particular importance during geomagnetic storms when the dynamics of the tail control substorm activity. To investigate this, we use the Gorgon MHD model to simulate a geomagnetic storm which commenced on 3 May 2014, and was host to multiple By and Bz reversals and a prolonged period of southward IMF driving. We find that the twisting of the current sheet is well-correlated to IMF By throughout the event, with the angle of rotation increasing linearly with downtail distance and being morepronounced when the tail contains less open flux. During periods of southward IMF the twisting of the central current sheet responds most strongly at a timelag of ∼ 100 min for distances beyond 20 RE, consistent with the 1-2 hr convection timescale identified in the open flux content. Under predominantly northward IMF the response of the twisting is bimodal, with the strongest correlations between 15-40 RE downtail being at a shorter timescale of ∼ 30 min consistent with that estimated for induced By due to wave propagation, compared to a longer timescale of ∼ 3 hr further downtail again attributed to convection. This indicates that asymmetries in the magnetotail communicated by IMF By are influenced mostly by global convection during strong solar wind driving, but that more prompt induced By effects can dominate in the near-Earth tail and during periods of weaker driving. These results provide new insight into the characteristic timescales of solar wind-magnetosphere-ionosphere coupling.
Smith AW, Forsyth C, Rae IJ, et al., 2022, On the considerations of using near real time data for space weather hazard forecasting, Space Weather, Vol: 20, ISSN: 1542-7390
Space weather represents a severe threat to ground-based infrastructure, satellites and communications. Accurately forecasting when such threats are likely (e.g., when we may see large induced currents) will help to mitigate the societal and financial costs. In recent years computational models have been created that can forecast hazardous intervals, however they generally use post-processed “science” solar wind data from upstream of the Earth. In this work we investigate the quality and continuity of the data that are available in Near-Real-Time (NRT) from the Advanced Composition Explorer and Deep Space Climate Observatory (DSCOVR) spacecraft. In general, the data available in NRT corresponds well with post-processed data, however there are three main areas of concern: greater short-term variability in the NRT data, occasional anomalous values and frequent data gaps. Some space weather models are able to compensate for these issues if they are also present in the data used to fit (or train) the model, while others will require extra checks to be implemented in order to produce high quality forecasts. We find that the DSCOVR NRT data are generally more continuous, though they have been available for small fraction of a solar cycle and therefore DSCOVR has experienced a limited range of solar wind conditions. We find that short gaps are the most common, and are most frequently found in the plasma data. To maximize forecast availability we suggest the implementation of limited interpolation if possible, for example, for gaps of 5 min or less, which could increase the fraction of valid input data considerably.
Phan TD, Verniero JL, Larson D, et al., 2022, Parker solar probe observations of solar wind energetic proton beams produced by magnetic reconnection in the near‐sun heliospheric current sheet, Geophysical Research Letters, Vol: 49, ISSN: 0094-8276
We report observations of reconnection exhausts in the Heliospheric Current Sheet (HCS) during Parker Solar Probe Encounters 08 and 07, at 16 Rs and 20 Rs, respectively. Heliospheric current sheet (HCS) reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ∼3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. Furthermore, protons were energized to super-thermal energies. During E08, energized protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was not the local HCS reconnection exhaust.
Eggington J, Desai R, Mejnertsen L, et al., 2022, Time-varying magnetopause reconnection during sudden commencement: global MHD simulations, Journal of Geophysical Research: Space Physics, Vol: 127, ISSN: 2169-9380
In response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). Whilst such compressions have also been associated with a contraction of the ionospheric polar cap due to the triggering of reconnection in the magnetotail, the effect of any changes in dayside reconnection is less clear and is a key component in fully understanding the system response. In this study we explore the time-dependent nature of dayside coupling during SC by performing global simulations using the Gorgon MHD code, and impact the magnetosphere with a series of interplanetary shocks with different parameters. We identify the location and evolu tion of the reconnection region in each case as the shock propagates through the magnetosphere, finding strong enhancement in the dayside reconnection rate and prompt expansion of the dayside polar cap prior to the eventual triggering of tail reconnection. This effect pervades for a variety of IMF orientations, and the reconnection rate is most enhanced for events with higher dynamic pressure. We explain this by repeating the simulations with a large explicit resistivity, showing that compression of the magnetosheath plasma near the propagating shock front allows for reconnection of much greater intensity and at different locations on the dayside magnetopause than during typical solar wind conditions. The results indicate that the dynamic behaviour of dayside coupling may render steady models of reconnection inaccurate during the onset of a severe space weather event.
Adhikari S, Shay MA, Parashar TN, et al., 2022, Reconnection and Turbulence: A Qualitative Approach to their Relationship
<jats:p>&lt;p&gt;Over the past few decades, the relationship between turbulence and reconnection has emerged as a subject of interest. For example, various properties of reconnection have been studied in different turbulent environments using plasma simulations. In other approaches, reconnection is studied as a subsidiary process occurring in turbulence. Turbulent features are also studied as consequences of instabilities associated with large scale reconnection. Only recently, we have attempted to answer some of the fundamental questions such as: &amp;#8220;What are the turbulent-like features of laminar magnetic reconnection?&amp;#8221;, &quot;Is magnetic reconnection fundamentally an energy cascade?&quot; both related to the interplay between reconnection and turbulence. Using 2.5D particle in cell simulations, we have found that laminar magnetic reconnection in a quasi-steady phase exhibits a Kolmogorov-like power spectrum. Most notably, the energy transfer process in magnetic reconnection is also found to be similar to that of a turbulent system suggesting that reconnection involves an energy cascade. The reconnection rate is correlated to both the magnetic energy spectrum in the ion-scales and the cascade of energy. Further, similarities between reconnection and turbulence in terms of the electric field spectrum, their components, and pressure-strain interaction will be highlighted.&lt;/p&gt;</jats:p>
Robertson S, Eastwood J, Stawarz J, et al., 2022, Survey of EDR-associated Magnetopause Flux Ropes with MMS
<jats:p>&lt;p&gt;Flux ropes are twisted magnetic field structures produced during magnetic reconnection. They are thought to be important for energy transport and particle acceleration and are commonly observed throughout space plasma environments, including at the Earth&amp;#8217;s magnetopause. Flux Transfer Events (FTEs), which typically contain flux ropes, have been observed to grow in size and flux content as they are convected over the magnetopause and into the magnetotail, contributing to flux transport in the Dungey cycle. More recently, small-scale flux ropes have been observed inside the Electron Diffusion Region (EDR) during magnetopause reconnection.&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;br&gt;In this study, we investigate the link between the EDR and flux ropes, presenting a survey of 245 flux ropes observed by the Magnetospheric Multiscale (MMS) mission on days during which the spacecraft also encountered the EDR. MMS measures the thermal electron and ion 3D distributions at 30 msec and 150 msec time resolution, respectively, and at spacecraft separations down to a few kilometres allowing the study of such electron-scale phenomena. We find that flux ropes are more likely to be observed closer to the EDR, and that flux ropes observed closer to the EDR tend to have greater axial magnetic field strength and therefore greater flux content. We suggest that we could be sampling a subset of flux ropes that are recently formed by the EDR and discuss how this impacts current theories for flux rope evolution on the magnetopause.&lt;/p&gt;</jats:p>
LaMoury A, Hietala H, Eastwood J, et al., 2022, Magnetosheath jets at the magnetopause: reconnection onset conditions
<jats:p>&lt;p&gt;Magnetosheath jets are localised pulses of high dynamic pressure plasma observed in Earth&amp;#8217;s magnetosheath. They are believed to form from the interaction between the solar wind and ripples in Earth&amp;#8217;s collisionless bow shock, before propagating into the turbulent magnetosheath. Upon impacting the magnetopause, jets can influence magnetospheric dynamics. In particular, previous studies have suggested that, by virtue of their internal magnetic field orientations, jet impacts may be able to trigger local magnetic reconnection at the magnetopause. This is most notable during traditionally unfavourable solar wind conditions, such as intervals of northward interplanetary magnetic field. This idea has been supported by a small number of case studies and simulations. We present a large statistical study into the properties of jets near the magnetopause. We examine the components of the magnetic reconnection onset condition &amp;#8211; the competing effects of magnetic shear angle and plasma beta &amp;#8211; to determine how jets may affect magnetopause reconnection in a statistical sense. We find that, due to their increased beta, jet plasma is typically not favourable to reconnection, often more so than the non-jet magnetosheath. Most jets do contain some reconnection-favourable plasma, however, suggesting that jets may be able to both trigger and suppress magnetopause reconnection. We complement this with new case studies of jets interacting with the magnetopause.&lt;/p&gt;</jats:p>
Stawarz JE, Eastwood JP, Phan T, et al., 2022, Turbulence-driven magnetic reconnection and the magnetic correlation length in collisionless plasma turbulence
<jats:p>&lt;p&gt;&lt;span&gt;Observations of Earth&amp;#8217;s magnetosheath from the Magnetospheric Multiscale (MMS) mission have provided an unprecedented opportunity to examine the detailed structure of the multitude of thin current sheets that are generated by plasma turbulence, revealing that a novel form of magnetic reconnection, which has come to be known as electron-only reconnection, can occur within magnetosheath turbulence. These electron-only reconnection events occur at thin electron-scale current sheets and have super-Alfv&amp;#233;nic electron jets that can approach the electron Alfv&amp;#233;n speed; however, they do not appear to have signatures of ion jets. It is thought that electron-only reconnection can occur when the length of the reconnecting current sheets along the outflow direction is short enough that the ions cannot fully couple to the newly reconnected magnetic field lines before they fully relax. In this work, we examine how the correlation length of the magnetic fluctuations in a turbulent plasma, which constrains the length of the current sheets that can be formed by the turbulence, impacts the nature of turbulence-driven magnetic reconnection. Using observations from MMS, we systematically examine 60 intervals of magnetosheath turbulence &amp;#8211; identifying 256 small-scale reconnection events, both with and without ion jets. We demonstrate that the properties of the reconnection events transition to become more consistent with electron-only reconnection when the magnetic correlation length of the turbulence is below ~20 ion inertial lengths. We further discuss the implications of the results in the context of other turbulent plasmas by considering observations of turbulent fluctuations in the solar wind. &lt;br&gt;&lt;/span&gt;&lt;/p&gt;</jats:p>
Desai R, Eastwood J, Eggington J, et al., 2022, Magnetospheric compressions, magnetopause shadowing and the last-closed-drift-shell
<jats:p>&lt;p&gt;Fluxes in the outer radiation belt can vary by orders of magnitude in response to solar wind driving conditions. Magnetopause shadowing, where electron and proton drift paths intersect the magnetopause boundary, is a fundamental loss process which operates on sub-day timescales and can result in rapid loss across the outer radiation belt. Accurate characterisation of this is therefore required to fully account for outer radiation belt dynamics and to avoid unrealistic fluxes impacting long-term forecasts. In this paper we utilise particle simulations of the radiation belts integrated within evolving global MHD simulations, to provide high-resolution high-fidelity simulations of the phenomenon of magnetopause shadowing. We model a variety of magnetopause compression scenarios corresponding to extreme cases of interplanetary shock impacts, and gradual increases in solar wind dynamic pressure. We thus constrain how time-dependent topological variation of the magnetospheric fields results in a complex interplay of open and closed particle drift paths, and examine the role of the electric field in modulating escaping particles trajectories as well as corresponding prompt injections into the inner magnetosphere.&lt;/p&gt;</jats:p>
Maffei S, Livermore P, Mound J, et al., 2022, The future evolution of the auroral zones
<jats:p>&lt;p&gt;The auroral zones indicate the locations on the Earth&amp;#8217;s surface where, on average, it is most likely to spot aurorae as a consequence of increased solar activity. The shape of the auroral zones and, similarly, the geographical locations most vulnerable to extreme space weather events are modulated by the geomagnetic field of internal origin. As the latter evolves in time, the formers will be subject to variations on the same timescales.&lt;/p&gt;&lt;p&gt;From available geomagnetic field forecasts (which provide an estimate of the future evolution of the geomagnetic field of internal origin) we derive AACGM latitudes and estimate the future evolution of the auroral zones. The novel aspect of this technique is that we make use of all available Gauss coefficients to produce the forecasts, while the majority of present techniques estimate the location of the auroral zones based on the dipolar coefficients only. Our results show that, while the shift of the geomagnetic dipole axis has a first order contribution, higher order Gauss coefficients contribute significantly to the location and shape of the auroral zones.&lt;/p&gt;&lt;p&gt;The same technique is then extended to estimate the future location of the geographical location that would be, on average, most exposed to extreme space weather event. We find that the space-weather related risk will not change significantly for the UK over the next 50 years. For the Canadian provinces of Quebec and Ontario, however, we predict a significant increase in the risk associated to extreme solar activity.&lt;/p&gt;</jats:p>
Rodriguez L, Barnes D, Hosteaux S, et al., 2022, Comparing the heliospheric cataloging, analysis, and techniques service (HELCATS) manual and automatic catalogues of coronal mass ejections using solar terrestrial relations observatory/heliospheric Imager (STEREO/HI) Data, Solar Physics: a journal for solar and solar-stellar research and the study of solar terrestrial physics, Vol: 297, ISSN: 0038-0938
We present the results of a comparative study between automatic and manually compiled coronal mass ejection (CME) catalogues based on observations from the Heliospheric Imagers (HIs) onboard NASA’s Solar Terrestrial Relations Observatory (STEREO) spacecraft. Using the Computer Aided CME Tracking software (CACTus), CMEs are identified in HI data using an automatic feature-detection algorithm, while the Heliospheric Imagers Catalogue (HICAT) includes CMEs that are detected by visual inspection of HI images. Both catalogues were compiled as part of the EU FP7 Heliospheric Cataloguing, Analysis and Techniques Service (HELCATS) project (www.helcats-fp7.eu). We compare observational parameters of the CMEs from CACTus to those listed in HICAT, such as CME frequency, position angle (PA), and PA-width. We also compare CACTus-derived speeds to speeds derived from applying geometric modelling to the majority of the HICAT CMEs, the results of which are listed in the HELCATS Heliospheric Imagers Geometric Catalogue (HIGeoCAT). We find that both CACTus and HICAT catalogues contain a similar number of events when we exclude events narrower than 20∘, which are not included in the HICAT catalogue but are found to be identified by CACTus. PA-distributions are strongly peaked around 90∘ and 270∘, with a slightly larger CME frequency northwards of the equatorial plane (particularly for the STEREO-A versions of both catalogues). The CME PA-widths in both HICAT and CACTus catalogues peak at approximately 60∘. Manually derived speeds from HIGeoCAT and automatically derived speeds by CACTus correlate well for values lower than 1000 km s−1, in particular when CMEs are propagating close to the plane of the sky.
Stawarz J, Eastwood J, Phan T, et al., 2022, Turbulence-driven magnetic reconnection and the magnetic correlation length: observations from magnetospheric multiscale in Earth's magnetosheath, Physics of Plasmas, Vol: 29, Pages: 1-20, ISSN: 1070-664X
Turbulent plasmas generate a multitude of thin current structures that can be sites for magnetic reconnection. The Magnetospheric Multiscale (MMS) mission has recently enabled the detailed examination of such turbulent current structures in Earth's magnetosheath and revealed that a novel type of reconnection, known as electron-only reconnection, can occur. In electron-only reconnection, ions do not have enough space to couple to the newly reconnected magnetic fields, suppressing ion jet formation and resulting in thinner sub-proton-scale current structures with faster super-Alfvénic electron jets. In this study, MMS observations are used to examine how the magnetic correlation length (λC) of the turbulence, which characterizes the size of the large-scale magnetic structures and constrains the length of the current sheets formed, influences the nature of turbulence-driven reconnection. We systematically identify 256 reconnection events across 60 intervals of magnetosheath turbulence. Most events do not appear to have ion jets; however, 18 events are identified with ion jets that are at least partially coupled to the reconnected magnetic field. The current sheet thickness and electron jet speed have a weak anti-correlation, with faster electron jets at thinner current sheets. When 𝜆𝐶≲20 ion inertial lengths, as is typical near the sub-solar magnetosheath, a tendency for thinner current sheets and potentially faster electron jets is present. The results are consistent with electron-only reconnection being more prevalent for turbulent plasmas with relatively short λC and may be relevant to the nonlinear dynamics and energy dissipation in turbulent plasmas.
Eckersley S, Rowe S, Antoniou N, et al., 2022, A Distributed Space-Weather Sensor System using Small Satellites, ISSN: 0074-1795
Space weather is becoming increasingly important for space and terrestrial activities and is likely to transition to an operational service. Small satellites are ideally suited for space-weather measurements given the need for making simultaneous measurements across both small and large volumes of space. The “Nanosatellites for D3S” Phase 0/A study for ESA was initiated in early 2021 with the objective to assess the feasibility of using nanosatellites for future operational space weather monitoring missions in near-Earth space as part of ESA's Distributed Space Weather Sensor System (D3S) - which itself forms part of the wider ESA Enhanced Space Weather Monitoring System. The study team consortium is highly experienced including sub-contractors supporting SSTL from MSSL, Imperial College London, and VZLU. Surrey Space Centre and Northumbria University are also providing expert consultancy. In the first part of the Phase 0 study, a survey of the measurement requirements and potential space weather instruments was carried out, alongside an investigation into recent relevant nanosatellite missions and future nanosatellite technologies. This was followed by an analysis and trade-off of high level mission architecture concepts eventually converging down to two of the most promising mission architecture concepts, which were further analysed in the latter half of the Phase 0 study. The objective of the first Phase 0 mission architecture concept was to provide near-real time measurements of radiation, thermal plasma and Ionospheric neutrals/plasma, via a constellation of 20x SSTL-21 satellites, in a single LEO orbital plane. The objective of the second Phase 0 mission architecture concept was to provide near-real time measurements of radiation, the Ionosphere and the Thermosphere, via a constellation of 6x 16U SSTL-Cube satellites, in a single LEO orbital plane. The orbit selected for both missions was a 500-600km Sun-Synchronous LEO Orbit with an LTAN of 10:30a
Adhikari S, Parashar TN, Shay MA, et al., 2021, Energy transfer in reconnection and turbulence, Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, Vol: 104, ISSN: 1539-3755
Reconnection and turbulence are two of the most commonly observed dynamical processes in plasmas, but their relationship is still not fully understood. Using 2.5D kinetic particle-in-cell simulations of both strong turbulence and reconnection, we compare the cross-scale transfer of energy in the two systems by analyzing the generalization of the von Kármán Howarth equations for Hall magnetohydrodynamics, a formulation that subsumes the third-order law for steady energy transfer rates. Even though the large scale features are quite different, the finding is that the decomposition of the energy transfer is structurally very similar in the two cases. In the reconnection case, the time evolution of the energy transfer also exhibits a correlation with the reconnection rate. These results provide explicit evidence that reconnection dynamics fundamentally involves turbulence-like energy transfer.
Eastwood JP, Stawarz JE, Phan TD, et al., 2021, Solar Orbiter observations of an ion-scale flux rope confined to a bifurcated solar wind current sheet, Astronomy & Astrophysics, Vol: 656, Pages: 1-8, ISSN: 0004-6361
Context. Flux ropes in the solar wind are a key element of heliospheric dynamics and particle acceleration. When associated withcurrent sheets, the primary formation mechanism is magnetic reconnection and flux ropes in current sheets are commonly used astracers of the reconnection process.Aims. Whilst flux ropes associated with reconnecting current sheets in the solar wind have been reported, their occurrence, sizedistribution, and lifetime are not well understood.Methods. Here we present and analyse new Solar Orbiter magnetic field data reporting novel observations of a flux rope confined toa bifurcated current sheet in the solar wind. Comparative data and large-scale context is provided by Wind.Results. The Solar Orbiter observations reveal that the flux rope, which does not span the current sheet, is of ion scale, and in areconnection formation scenario, existed for a prolonged period of time as it was carried out in the reconnection exhaust. Wind is alsofound to have observed clear signatures of reconnection at what may be the same current sheet, thus demonstrating that reconnectionsignatures can be found separated by as much as ∼ 2 000 Earth radii, or 0.08 au.Conclusions. The Solar Orbiter observations provide new insight into the hierarchy of scales on which flux ropes can form, and showthat they exist down to the ion scale in the solar wind. The context provided by Wind extends the spatial scale over which reconnectionsignatures have been found at solar wind current sheets. The data suggest the local orientations of the current sheet at Solar Orbiterand Wind are rotated relative to each other, unlike reconnection observed at smaller separations; the implications of this are discussedwith reference to patchy vs. continuous reconnection scenarios.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.