Publications
117 results found
Montagud-Camps V, Toledo-Redondo S, Hellinger P, et al., 2024, An unbiased view of the contributions to turbulence cascade in Earth's magnetosheath.
<jats:p>Earth's magnetosheath is a medium where plasma parameters can take a wide range of values and where plasma fluid properties can vary greatly, depending on the distance to the bow shock and the upstream solar wind conditions. Plasma turbulence that develops in the magnetosheath is also affected by these changes, thus giving rise to a similar variety of turbulence regimes.With the data collected during the MMS unbiased magnetosheath campaign, it is now possible to explore the plasma parameter space of the magnetosheath and study turbulence properties with a set of high-cadence in-situ measurements. This dataset was gathered from February 1st 2023 to April 1st 2023 and consists of 15 inbound magnetosheath crossings from which 300 burst-data intervals were collected. During each crossing, the burst-mode measurements were taken for 3 minutes every 6 minutes, without imposing any selection criteria to collect the data. The length of the time intervals and their time resolution make them suitable to study the turbulent dynamics around the ion spectral break.In this work we will study the different contributions to the energy cascade rate (measured by means of scaling laws derived from the Hall-MHD equations) and their dependence on plasma conditions, like the plasma beta, and turbulence properties, such as the spectral index and turbulence anisotropy.</jats:p>
Stawarz JE, Quijia Pilapaña P, Pyakurel PS, et al., 2024, Assessing the Role of Turbulence-Driven Magnetic Reconnection in the Dissipation of Plasma Turbulence in Earth&#8217;s Magnetosheath
<jats:p>Magnetic reconnection has long been thought to play an important role in turbulent plasmas &#8211; with the nonlinear dynamics of turbulent systems being well known to self-consistently generate intense current structures and associated magnetic shears that can be sites where so-called turbulence-driven magnetic reconnection can occur. However, complex three-dimensional magnetic topologies and the small-scale nature of these magnetic reconnection events have traditionally made it challenging to assess the role of magnetic reconnection in the turbulent dynamics from either a numerical or observational perspective. Recent high-resolution observations from NASA&#8217;s Magnetospheric Multiscale (MMS) mission have provided an unprecedented new opportunity to systematically examine turbulence-driven reconnection in the region of shock-driven turbulence within Earth&#8217;s magnetosheath. These observations have provided new insight into the nature of magnetic reconnection within turbulent plasmas, revealing that under the right conditions so-called electron-only magnetic reconnection, in which ion jets are not accelerated by the newly reconnected magnetic fields, can occur. In this talk, we explore how to observationally constrain the contribution turbulence-driven magnetic reconnection makes to the energy dissipation rate of the turbulence. We then directly compare estimates of the dissipation rate associated with reconnection events observed by MMS to estimates of the turbulent energy cascade rate for the specific intervals of magnetosheath turbulence that the reconnection events are observe within. The potential implications of traditional ion-coupled reconnection versus electron-only reconnection for the energy budget of turbulent dissipation and the magnetosheath overall are then discussed in detail.</jats:p>
Fargette N, Eastwood J, Waters C, et al., 2024, On the evolution of magnetic reconnection in the solar wind
<jats:p>Magnetic reconnection is a fundamental process in astrophysical plasma, as it enables the dissipation of energy at kinetic scales as well as large-scale reconfiguration of the magnetic topology. In the solar wind, its quantitative role in plasma dynamics and particle energization remains an open question that is starting to come into focus as more missions now probe the inner heliosphere. To more efficiently detect magnetic reconnection in-situ using automated and modern methods is one of the challenges that can bring us closer to understanding the impact of magnetic reconnection on its surrounding magnetized environment.In this presentation, we make use of existing databases to focus on the evolution of magnetic reconnection properties through the heliosphere, using several space missions such as Parker Solar Probe (PSP), Solar Orbiter and Wind. We investigate the properties of small-scale reconnecting current sheets found in the turbulent solar wind as a function of radial distance and plasma source. In parallel, we also make use of PSP-Solar Orbiter alignments to study how the large-scale and high-shear reconnection occurring at the heliospheric current sheet evolves as it propagates in the solar wind. Finally, we emphasize how reconnection has a high impact on coherent structure evolution such as coronal mass ejection erosion or merging.Collectively, these results show that magnetic reconnection is ubiquitous in the solar wind and occurs in a wide variety of settings, with a high impact on its surrounding environment. We discuss how the recent growth of available in-situ spacecraft mission data inside the Earth orbit promises further substantial progress in our understanding of magnetic reconnection occurrence, properties and impact in the solar wind.&#160;</jats:p>
Matteini L, Tenerani A, Landi S, et al., 2024, Alfvénic fluctuations in the expanding solar wind: Formation and radial evolution of spherical polarization, Physics of Plasmas, Vol: 31, ISSN: 1070-664X
We investigate properties of large-scale solar wind Alfvénic fluctuations and their evolution during radial expansion. We assume a strictly radial background magnetic field B ∥ R , and we use two-dimensional hybrid (fluid electrons, kinetic ions) simulations of balanced Alfvénic turbulence in the plane orthogonal to B ; the simulated plasma evolves in a system comoving with the solar wind (i.e., in the expanding box approximation). Despite some model limitations, simulations exhibit important properties observed in the solar wind plasma: Magnetic field fluctuations evolve toward a state with low-amplitude variations in the amplitude B = | B | and tend to a spherical polarization. This is achieved in the plasma by spontaneously generating field aligned, radial fluctuations that suppress local variations of B, maintaining B ∼ const. spatially in the plasma. We show that within the constraint of spherical polarization, variations in the radial component of the magnetic field, BR lead to a simple relation between δ B R and δ B = | δ B | as δ B R ∼ δ B 2 / ( 2 B ) , which correctly describes the observed evolution of the rms of radial fluctuations in the solar wind. During expansion, the background magnetic field amplitude decreases faster than that of fluctuations so that their the relative amplitude increases. In the regime of strong fluctuations, δ B ∼ B , this causes local magnetic field reversals, consistent with solar wind switchbacks.
Smith AW, Rae IJ, Stawarz JE, et al., 2024, Automatic Encoding of Unlabeled Two Dimensional Data Enabling Similarity Searches: Electron Diffusion Regions and Auroral Arcs, Journal of Geophysical Research: Space Physics, Vol: 129, ISSN: 2169-9380
Critically important phenomena in Earth’s magnetosphere often occur briefly, or in small spatial regions. These processes are sampled with orbiting spacecraft or by fixed ground observatories and so rarely appear in data. Identifying such intervals can be an incredibly time consuming task. We apply a novel, powerful method by which two dimensional data can be automatically processed and embeddings created that contain key features of the data. The distance between embedding vectors serves as a measure of similarity. We apply the state-of-the-art method to two example datasets: MMS electron velocity distributions and auroral all sky images. We show that the technique creates embeddings that group together visually similar observations. When provided with novel example images the method correctly identifies similar intervals: when provided with an electron distribution sampled during an encounter with an electron diffusion region the method recovers similar distributions obtained during two other known diffusion region encounters. Similarly, when provided with an interesting auroral structure the method highlights the same structure observed from an adjacent location and at other close time intervals. The method promises to be a useful tool to expand interesting case studies to multiple events, without requiring manual data labeling. Further, the models could be fine-tuned with relatively small set of labeled example data to perform tasks such as classification. The embeddings can also be used as input to deep learning models, providing a key intermediary step—capturing the key features within the data.
Blasl KA, Nakamura TKM, Nakamura R, et al., 2023, Electron-Scale Reconnecting Current Sheet Formed Within the Lower-Hybrid Wave-Active Region of Kelvin-Helmholtz Waves, GEOPHYSICAL RESEARCH LETTERS, Vol: 50, ISSN: 0094-8276
Shi P, Scime EE, Barbhuiya MH, et al., 2023, Using Direct Laboratory Measurements of Electron Temperature Anisotropy to Identify the Heating Mechanism in Electron-Only Guide Field Magnetic Reconnection., Phys Rev Lett, Vol: 131
Anisotropic electron heating during electron-only magnetic reconnection with a large guide magnetic field is directly measured in a laboratory plasma through in situ measurements of electron velocity distribution functions. Electron heating preferentially parallel to the magnetic field is localized to one separatrix, and anisotropies of 1.5 are measured. The mechanism for electron energization is identified as the parallel reconnection electric field because of the anisotropic nature of the heating and spatial localization. These characteristics are reproduced in a 2D particle-in-cell simulation and are also consistent with numerous magnetosheath observations. A measured increase in the perpendicular temperature along both separatrices is not reproduced by our 2D simulations. This work has implications for energy partition studies in magnetosheath and laboratory reconnection.
Bessho N, Chen L-J, Hesse M, et al., 2023, Electron Acceleration and Heating during Magnetic Reconnection in the Earth's Quasi-parallel Bow Shock, ASTROPHYSICAL JOURNAL, Vol: 954, ISSN: 0004-637X
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.
Lewis HC, Stawarz JE, Franci L, et al., 2023, Magnetospheric Multiscale measurements of turbulent electric fields in earth's magnetosheath: How do plasma conditions influence the balance of terms in generalized Ohm's law?, PHYSICS OF PLASMAS, Vol: 30, ISSN: 1070-664X
Usanova ME, Ergun RE, Stawarz JE, 2023, Ion Energization by Turbulent Electric Fields in Fast Earthward Flows and Its Implications for the Dynamics of the Inner Magnetosphere, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380
Roberts OW, Voeroes Z, Torkar K, et al., 2023, Estimation of the Error in the Calculation of the Pressure-Strain Term: Application in the Terrestrial Magnetosphere, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380
Halford AJ, Stawarz JE, Allen RC, et al., 2023, An Inclusive Heliophysics Community, Vol. 55, Issue 3 (Heliophysics 2024 Decadal Whitepapers)
Halford AJ, Stawarz JE, Allen RC, et al., 2023, Mentorship within Heliophysics, Vol. 55, Issue 3 (Heliophysics 2024 Decadal Whitepapers)
Halford AJ, Stawarz JE, Dong C, et al., 2023, The Importance of Policies: It’s not just a pipeline problem, Vol. 55, Issue 3 (Heliophysics 2024 Decadal Whitepapers)
Franci L, Papini E, Del Sarto D, et al., 2023, On the nature of electric field fluctuations in the near-Sun solar wind and its implication for the turbulent energy transfer at ion and electron scales
<jats:p>We model plasma turbulence in the near-Sun solar wind by means of a high-resolution fully kinetic simulation initialised with average plasma conditions measured by Parker Solar Probe during its first solar encounter. Once turbulence is fully developed, the power spectra of the plasma and electromagnetic fluctuations exhibit clear power-law intervals down to sub-electron scales. Our simulation models the electron-scale electric field fluctuations with unprecedented accuracy. This allows us to perform the first detailed analysis of the different terms of the electric field in the generalised Ohm's law (MHD, Hall, and electron pressure terms) at ion and electron scales, both in physical space and in Fourier space. Such analysis suggests rewriting the Ohm&#8217;s law in a different form, which disentangles the contribution of different underlying plasma mechanisms, characterising the nature of the electric field fluctuations in the different range of scales. This provides a new insight on how energy in the turbulent electromagnetic fields is transferred through ion and electron scales and seems to favour the role of pressure-balanced structures versus waves. We finally test our assumptions and numerical results by means of a statistical analysis using magnetic field, electric field, and electron density data from Solar Orbiter and Parker Solar Probe. Preliminary results show good agreement with our theoretical expectations inspired by our simulation.</jats:p>
Stawarz JE, Woodham L, Laker R, et al., 2023, The Evolution of Turbulence in the Inner Heliosphere: Insights from the February 2022 Radial Alignment between Parker Solar Probe and Solar Orbiter
<jats:p>The solar wind is filled with complex turbulent dynamics that transfer energy from large length scales to progressively smaller scales. This transfer of energy generates a multitude of thin structures, such as current sheets, in the plasma with a preference for forming particularly strong gradients &#8211; a property know as intermittency &#8211; that are thought to play a role in turbulent dissipation. One of the important problems in the study of solar wind turbulence is understanding how and to what extent the nature of the turbulent dynamics vary as the solar wind expands from the Sun. However, disentangling the dynamical evolution of the turbulence from variations in the properties of different solar wind streams and temporal variations in the source region of a given stream has traditionally been challenging in the solar wind. We make use of a fortuitous alignment between NASA&#8217;s Parker Solar Probe and ESA&#8217;s Solar Orbiter spacecraft, which occurred at the end of February 2022, to examine how the turbulent fluctuations in the solar wind evolve with radial distance. During this radial alignment the two spacecraft observed the same stream of solar wind plasma, and potentially nearly the same parcel of plasma, at two different radial distances allowing us to separate the evolution with radial distance from the other sources of variability. We explore both the statistical properties of the fluctuations as well as the nature of the most intermittent structures observed by the spacecraft at different length scales in the plasma. The results demonstrate that, while the intermittent fluctuations in the components perpendicular to the radial direction are statistically similar at different radial distances, the intermittency properties in the radial direction can significantly change with distance. Comparisons of the observational results with expanding box simulations of turbulence suggest that some of the key fe
Lewis H, Stawarz J, Franci L, et al., 2023, Generalised Ohm’s Law in the Magnetosheath: How do plasma conditions impact turbulent electric fields?
<jats:p>Turbulence is a complex phenomenon whereby fluctuation energy is transferred between different scale sizes as a result of nonlinear interactions. Electromagnetic turbulence is ubiquitous within space plasmas, wherein it is associated with numerous nonlinear interactions. The dynamics of the magnetic field, which are widely studied in turbulence theory, are intimately linked to the electric field, which controls the exchange of energy between the magnetic field and the particles. Magnetospheric Multiscale (MMS) provides the unique opportunity to decompose electric field dynamics into contributions from different linear and nonlinear processes. The evolution of the electric field is described by generalised Ohm&#8217;s law, which breaks down the dynamics into components arising from different physical effects. Using high-resolution multipoint measurements, we compute the MHD, Hall and Electron Pressure terms of generalised Ohm&#8217;s law for 60 turbulent magnetosheath intervals. These terms, which have varying contributions to the dynamics as a function of scale, arise as a result of different physical effects related to a range of underlying turbulent phenomena. We examine how two characteristics of the turbulent electric field spectra depend on plasma conditions: the transition scale between MHD and Hall dominance (the &#8216;Hall scale&#8217;, kHall) and the relative amplitude of Hall and Electron Pressure contributions. Motivated by dimensional analysis arguments which appeal to characteristics of the plasma and the turbulence that can be quantified in a number of ways by MMS, we demonstrate the necessary refinements required to reproduce measured values. The scalar isotropic kinetic Alfven wave prediction for the ratio of Electron Pressure to Hall terms as a function of plasma beta is not consistent with measurements. We observe that the MHD and Hall terms are dominated by either nonlinear or linear dynamics, dependi
Pyakurel PS, Phan TD, Drake JF, et al., 2023, On the Short-scale Spatial Variability of Electron Inflows in Electron-only Magnetic Reconnection in the Turbulent Magnetosheath Observed by MMS, ASTROPHYSICAL JOURNAL, Vol: 948, ISSN: 0004-637X
Stawarz JEE, Genestreti KJJ, 2023, Preface to Special Topic: Plasma Physics from the Magnetospheric Multiscale Mission, PHYSICS OF PLASMAS, Vol: 30, ISSN: 1070-664X
Shuster JR, Gershman DJ, Giles BL, et al., 2023, Temporal, Spatial, and Velocity-Space Variations of Electron Phase Space Density Measurements at the Magnetopause, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 128, ISSN: 2169-9380
Perrone D, Perri S, Bruno R, et al., 2022, Evolution of coronal hole solar wind in the inner heliosphere: Combined observations by Solar Orbiter and Parker Solar Probe, ASTRONOMY & ASTROPHYSICS, Vol: 668, ISSN: 0004-6361
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Verscharen D, Wicks RT, Alexandrova O, et al., 2022, A case for electron-astrophysics, Experimental Astronomy: an international journal on astronomical instrumentation and data analysis, Vol: 54, Pages: 473-519, ISSN: 0922-6435
The smallest characteristic scales, at which electron dynamics determines the plasma behaviour, are the next frontier in space and astrophysical plasma research. The analysis of astrophysical processes at these scales lies at the heart of the research theme of electron-astrophysics. Electron scales are the ultimate bottleneck for dissipation of plasma turbulence, which is a fundamental process not understood in the electron-kinetic regime. In addition, plasma electrons often play an important role for the spatial transfer of thermal energy due to the high heat flux associated with their velocity distribution. The regulation of this electron heat flux is likewise not understood. By focussing on these and other fundamental electron processes, the research theme of electron-astrophysics links outstanding science questions of great importance to the fields of space physics, astrophysics, and laboratory plasma physics. In this White Paper, submitted to ESA in response to the Voyage 2050 call, we review a selection of these outstanding questions, discuss their importance, and present a roadmap for answering them through novel space-mission concepts.
Pathak N, Ergun RE, Qi Y, et al., 2022, Evidence of a Nonorthogonal X-line in Guide-field Magnetic Reconnection, ASTROPHYSICAL JOURNAL LETTERS, Vol: 941, ISSN: 2041-8205
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Laker R, Horbury TS, Matteini L, et al., 2022, Switchback deflections beyond the early parker solar probe encounters, Monthly Notices of the Royal Astronomical Society, Vol: 517, Pages: 1001-1005, ISSN: 0035-8711
Switchbacks are Aflvénic fluctuations in the solar wind, which exhibit large rotations in the magnetic field direction. Observations from Parker Solar Probe’s (PSP’s) first two solar encounters have formed the basis for many of the described switchback properties and generation mechanisms. However, this early data may not be representative of the typical near-Sun solar wind, biasing our current understanding of these phenomena. One defining switchback property is the magnetic deflection direction. During the first solar encounter, this was primarily in the tangential direction for the longest switchbacks, which has since been discussed as evidence, and a testable prediction, of several switchback generation methods. In this study, we re-examine the deflection direction of switchbacks during the first eight PSP encounters to confirm the existence of a systematic deflection direction. We first identify switchbacks exceeding a threshold deflection in the magnetic field and confirm a previous finding that they are arc-polarized. In agreement with earlier results from PSP’s first encounter, we find that groups of longer switchbacks tend to deflect in the same direction for several hours. However, in contrast to earlier studies, we find that there is no unique direction for these deflections, although several solar encounters showed a non-uniform distribution in deflection direction with a slight preference for the tangential direction. This result suggests a systematic magnetic configuration for switchback generation, which is consistent with interchange reconnection as a source mechanism, although this new evidence does not rule out other mechanisms, such as the expansion of wave modes.
Telloni D, Adhikari L, Zank GP, et al., 2022, Observation and Modeling of the Solar Wind Turbulence Evolution in the Sub-Mercury Inner Heliosphere, ASTROPHYSICAL JOURNAL LETTERS, Vol: 938, ISSN: 2041-8205
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Ergun RE, Pathak N, Usanova ME, et al., 2022, Observation of Magnetic Reconnection in a Region of Strong Turbulence, ASTROPHYSICAL JOURNAL LETTERS, Vol: 935, ISSN: 2041-8205
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Ergun RE, Usanova ME, Turner DL, et al., 2022, Bursty bulk flow turbulence as a source of energetic particles to the outer radiation belt, Geophysical Research Letters, Vol: 49, ISSN: 0094-8276
We report observations of a Bursty Bulk Flow (BBF) penetrating close to the outer edge of the radiation belt. The turbulent BBF braking region is characterized by ion velocity fluctuations, magnetic field (B) variations, and intense electric fields (E). In this event, energetic (>100 keV) electron and ion fluxes are appreciably enhanced. Importantly, fluctuations in energetic electrons and ions suggest local energization. Using correlation distances and other observed characteristics of turbulent E, test-particle simulations support local energization by E that favors higher-energy electrons and leads to an enhanced energetic shoulder and tail in the electron distributions. The energetic shoulder and tail could be amplified to MeV energies by adiabatic transport into the radiation belt where |B| is higher. This analysis suggests that turbulence generated by BBFs can, in part, supply energetic particles to the outer radiation belt and that turbulence can be a significant contributor to particle acceleration.
Bessho N, Chen L-J, Stawarz J, et al., 2022, Strong reconnection electric fields in shock-driven turbulence, Physics of Plasmas, Vol: 29, Pages: 1-23, ISSN: 1070-664X
Turbulent magnetic reconnection in a quasi-parallel shock under parameters relevant to the Earth's bow shock is investigated by means of a two-dimensional particle-in-cell simulation. The addressed aspects include the reconnection electric field, the reconnection rate, and the electron and the ion outflow speeds. In the shock transition region, many current sheets are generated in shock-driven turbulence, and electron-only reconnection and reconnection where both ions and electrons are involved can occur in those current sheets. The electron outflow speed in electron-only reconnection shows a positive correlation with the theoretical speed, which is close to the local electron Alfvén speed, and a strong convection electric field is generated by the large electron outflow. As a result, the reconnection electric field becomes much larger than those in the standard magnetopause or magnetotail reconnection. In shock-driven reconnection that involves ion dynamics, both electron outflows and ion outflows can reach of the order of 10 times the Alfvén speed in the X-line rest frame, leading to a reconnection electric field the same order as that in electron-only reconnection. An electron-only reconnection event observed by the magnetospheric multiscale mission downstream of a quasi-parallel shock is qualitatively similar to those in the simulation and shows that the outflow speed reaches approximately half the local electron Alfvén speed, supporting the simulation prediction.
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>
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