Marit Oieroset

• Ph.D.
• Research Physicist at University of California, Berkeley

Magnetic reconnection is an explosive energy release event. It plays an important role in accelerating particles to high non‐thermal energies. These particles often exhibit energy spectra characterized by a power‐law distribution. However, the partitioning of energy between thermal and non‐thermal components, and between ions and electrons, remains...

Particles are heated efficiently through energy conversion processes, such as shocks and magnetic reconnection, in collisionless plasma environments. While empirical scaling laws for the temperature increase have been obtained, the precise mechanism of energy partition between ions and electrons remains unclear. Here we show, based on coupled theor...

Magnetic reconnection is an explosive energy release event. It plays an important role in accelerating particles to high non-thermal energies. These particles often exhibit energy spectra characterized by a power-law distribution. However, the partitioning of energy between thermal and non-thermal components, and between ions and electrons, remains...

Particles are heated efficiently through energy conversion processes such as shocks and magnetic reconnection in collisionless plasma environments. While empirical scaling laws for the temperature increase have been obtained, the precise mechanism of energy partition between ions and electrons remains unclear. Here we show, based on coupled theoret...

Electrons are accelerated to high, non-thermal energies during explosive energy-release events in space, such as magnetic reconnection. However, the properties and acceleration mechanisms of relativistic electrons directly associated with reconnection X-line are not well understood. This study utilizes Magnetospheric Multiscale (MMS) measurements t...

The electron diffusion region (EDR) is a key region for magnetic reconnection, but the typical energy transport and conversion in EDRs is still not well understood. In this work, we perform a statistical study of 80 previously published near X‐line events identified at the dayside magnetopause in Magnetospheric Multiscale data. We find 44 events th...

We report observations of multiple subscale reconnecting current sheets embedded inside a large-scale heliospheric current sheet (HCS) reconnection exhaust. The discovery was made possible by the unusual skimming trajectory of Parker Solar Probe through a sunward-directed HCS exhaust, sampling structures convecting with the exhaust outflows for mor...

We survey 20 reconnection outflow events observed by Magnetospheric MultiScale in the low- β and high-Alfvén-speed regime of the Earth’s magnetotail to investigate the scaling of ion bulk heating produced by reconnection. The range of inflow Alfvén speeds (800–4000 km s ⁻¹ ) and inflow ion β (0.002–1) covered by this study is in a plasma regime tha...

We have surveyed 21 reconnection exhaust events observed by Magnetospheric MultiScale in the low-plasma- β and high-Alfvén-speed regime of the Earth’s magnetotail to investigate the scaling of electron bulk heating produced by reconnection. The ranges of inflow Alfvén speed and inflow electron β e covered by this study are 800–4000 km s ⁻¹ and 0.00...

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...

We investigate the detailed properties of electron inflow in an electron-only reconnection event observed by the four Magnetospheric Multiscale (MMS) spacecraft in the Earth's turbulent magnetosheath downstream of the quasi-parallel bow shock. The lack of ion coupling was attributed to the small-scale sizes of the current sheets, and the observed b...

We have performed a statistical survey to investigate possible diamagnetic drift suppression of magnetic reconnection using Magnetospheric Multiscale observations of interlinked magnetic field line events at Earth’s magnetopause. Our goal is to investigate a possible cause for the observed magnetic field pileup on the two sides of the thin reconnec...

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 spe...

Electrons in earth's magnetotail are energized significantly both in the form of heating and in the form of acceleration to non-thermal energies. While magnetic reconnection is considered to play an important role in this energization, it still remains unclear how electrons are energized and how energy is partitioned between thermal and non-thermal...

We report Magnetospheric Multiscale four-spacecraft observations of a thin reconnecting current sheet with weakly asymmetric inflow conditions and a guide field of approximately twice the reconnecting magnetic field. The event was observed at the interface of interlinked magnetic field lines at the flank magnetopause when the maximum spacecraft sep...

An important process affecting solar wind–Earth’s magnetosphere coupling is nonsteady dayside magnetic reconnection, observationally evidenced by a flux transfer event (FTE) that shows a bipolar variation of the magnetic field component normal to the magnetopause. FTEs often consist of two interlinked flux tubes, but, local kinetic processes betwee...

During three of its first five orbits around the Sun, Parker Solar Probe (PSP) crossed the large-scale heliospheric current sheet (HCS) multiple times and provided unprecedented detailed plasma and field observations of the near-Sun HCS. We report the common detections by PSP of reconnection exhaust signatures in the HCS at heliocentric distances o...

Aims. We report the observation by Parker Solar Probe (PSP) of magnetic structures in the solar wind that present a strong peak in their magnetic field magnitude with an embedded central current sheet. Similar structures have been observed, either at the Earth’s magnetopause and called interlinked flux tubes, or in the solar wind and called interpl...

Magnetopause Kelvin‐Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small‐scale mechanisms. Vortex‐induced reconnection (VIR) was predicted in simulations and recently observed using NASA's Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery...

We have used a large number of magnetopause crossings by the Magnetospheric Multiscale (MMS) mission to investigate macroscopic properties of this current sheet, with emphasis on the flanks of the magnetopause. Macroscopic features such as thickness, location, and motion of the magnetopause were calculated as a function of local time sector. The re...

Plain Language Summary The solar wind and the Earth's magnetosphere are two gigantic magnetic structures that collide constantly over our heads, in the near‐space environment. At the boundary of their interaction (the magnetopause), the fundamental process of magnetic reconnection can occur. It is there that dynamic magnetic structures called “flux...

Magnetic reconnection in current sheets converts magnetic energy into particle energy. The process may play an important role in the acceleration and heating of the solar wind close to the Sun. Observations from Parker Solar Probe ( PSP ) provide a new opportunity to study this problem, as it measures the solar wind at unprecedented close distances...

Magnetic reconnection in current sheets converts magnetic energy into particle energy. The process may play an important role in the acceleration and heating of the solar wind close to the Sun. Observations from Parker Solar Probe provide a new opportunity to study this problem, as it measures the solar wind at unprecedented close distances to the...

Change history: In this Letter, the y-axis values in Fig. 3f should go from 4 to −8 (rather than from 4 to −4), the y-axis values in Fig. 3h should appear next to the major tick marks (rather than the minor ticks), and in Fig. 1b, the arrows at the top and bottom of the electron-scale current sheet were going in the wrong direction; these errors ha...

Plain Language Summary The Earth and the solar wind magnetic fields interconnect through a process called magnetic reconnection. The newly reconnected magnetic field lines are strongly bent and accelerate particles, similar to a rubber band in a slingshot. In this paper we have used observations from NASA's Magnetospheric MultiScale spacecraft to i...

We present direct and scaled comparisons between laboratory and in situ space observations of magnetic reconnection with a guide field, comparing results from the Magnetospheric Multiscale Mission and the Magnetic Reconnection eXperiment (MRX). While Magnetospheric Multiscale Mission observations obtain high-resolution and fully kinetic data, MRX o...

Magnetic flux ropes of various scale sizes have been observed at the Earth's magnetopause for four decades. These multiple structures resulting from reconnection have complex internal field and plasma signatures, and evolve as they propagate along the dayside magnetopause. Here plasma and magnetic field observations from the Magnetospheric Multisca...

While double ion populations, with a cold population originating from the solar wind and a hotter one from the magnetosphere, are frequently observed in the low-latitude boundary layers at the Earth's magnetopause, similar double electron populations are observed less often. A preliminary study of magnetopause crossings characteristics was used to...

Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region1,2. On larger scales, ions couple to the newly reconnected magnetic-field lines and are...

Magnetospheric Multiscale observations are used to probe the structure and temperature profile of a guide field reconnection exhaust ~100 ion inertial lengths downstream from the X-line in the Earth's magnetosheath. Asymmetric Hall electric and magnetic field signatures were detected, together with a density cavity confined near 1 edge of the exhau...

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 m...

Magnetosheath high-speed jets—localized dynamic pressure enhancements typically of ∼1 Earth radius in size—impact the dayside magnetopause several times per hour. Here we present the first in situ measurements suggesting that such an impact triggered magnetopause reconnection. We use observations from the five THEMIS spacecraft in a string-of-pearl...

We report three spacecraft observations of a reconnecting magnetosheath current sheet with a guide field of unity, with THD and THE/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...

We report a 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 resul...

New Magnetospheric Multiscale (MMS) observations of small-scale (~7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multispacecraft techniques, allowing them to be identified as flux ropes, whose...

Supporting Information S1

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 t...

We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E||) with amplitudes on the order of 100 mV/m and display nonlinear characteristics that suggest a possible net E|...

Magnetic reconnection is an explosive energy-release process in laboratory, space and astrophysical plasmas. While magnetic fields can `break' and `reconnect' in a very small region called the electron diffusion region (EDR), there have been conflicting theories as to whether this region can be a place of rapid energization of plasmas. Here we repo...

Magnetic reconnection is an explosive energy-release process in laboratory, space and astrophysical plasmas. While magnetic fields can ‘break’ and ‘reconnect’ in a very small region called the electron diffusion region (EDR), there have been conflicting theories as to whether this region can be a place of rapid energization of plasmas. Here we repo...

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 elec...

Using high-resolution burst-mode THEMIS data, we have examined in detail the electron and ion edges of the reconnecting magnetopause and the associated magnetic topologies of 23 high-shear reconnecting magnetopause crossings. The electron edge is identified as the most earthward detection of entering magnetosheath electrons and the accompanying fir...

This paper describes the efforts of our Inter-Disciplinary Scientist (IDS) team to (a) establish the large-scale context for reconnection diffusion region encounters by MMS at the magnetopause and in the magnetotail, including the distinction between X-line and O-line encounters, that would help the identification of diffusion regions in spacecraft...

Electron bulk heating during magnetic reconnection with symmetric inflow conditions is examined using kinetic particle-in-cell (PIC) simulations. The degree of electron heating is well correlated with the inflowing Alfv\'en speed $c_{Ar}$ based on the reconnecting magnetic field through the relation $\Delta T_e = 0.033 \,m_i\,c_{Ar}^2$, where $\Del...

We have performed a detailed analysis of plasma and wave observations in a magnetic flux rope encountered by THEMIS-D at the subsolar magnetopause. The extent of the flux rope was ~ 270 ion skin depths in the outflow direction and it was flanked by two active X-lines producing colliding plasma jets in the flux rope core where ion heating and supra-...

Collisionless magnetic reconnection is considered to be one of the most important plasma phenomena because it governs the transport of energy, momentum and plasma in a wide variety of situations. In particular, understanding the central diffusion region is crucial to gaining a full understanding of the physics of reconnection. Although most diffusi...

Biểu đồ Sài rồi kìa, Thuật toán dựa vào hệ thống của ta cũng Sài rồi tề ..kaka, [1] We surveyed 79 magnetopause reconnection exhausts detected by the THEMIS spacecraft to investigate how the amount and anisotropy of electron bulk heating produced by reconnection depend on the inflow boundary conditions. We find that the amount of heating, ΔTe, is c...

This paper gives an overview of the insights into the magnetic reconnection process obtained by in-situ measurements across current sheets found in planetary magnetospheres and the solar wind. Emphasis is placed on results that might be of interest to the study of reconnection in regions where no in-situ observations are available. These results in...

We have performed a statistical study of THEMIS spacecraft crossings of the asymmetric dayside magnetopause to test the prediction that the diamagnetic drift of the X-line due to a plasma pressure gradient across the magnetopause can suppress magnetic reconnection. The study includes crossings both when reconnection exhausts were present and when t...

During intervals of southward IMF, magnetic reconnection can result in the formation of flux transfer events (FTEs) on the dayside magnetopause which travel along the magnetopause in the anti-sunward direction. Of particular interest is their fate and the role they play transporting solar wind plasma into the magnetosphere. We present the discovery...

NASA’s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth’s magnetotail; reconnection, particle acceleration, and turbulence in the Earth’s magnetosphe...

For the Earth magnetotail, the Svenes et al. 2008 statistical study infers that the lobe density is highly variable, in the range 0.007-0.092 cm^{-3}. Such inflow density variation modifies reconnection diffusion region physical processes and reconnection rate drastically [Wu et al., 2011a]. This paper studies observable reconnection signatures in...

The structure of the geomagnetic tail under northward IMF conditions has long been controversial. Various global magnetosphere models predict either a closed tail of relatively short extent or a tail that still contains some open flux but mostly closed flux that extends hundreds of RE down tail. A fortuitous encounter of the Wind spacecraft 125 RE...

The ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) mission consists of two satellites (probes) extracted from the Earth-orbiting five probe THEMIS mission in 2009 and placed in lunar orbit in mid-2011. Prior to their insertion into lunar orbit, from October 2010 the two ARTEMIS probes P1...

We report the direct detection by three THEMIS spacecraft of a magnetic flux rope flanked by two active X lines producing colliding plasma jets near the center of the flux rope. The observed density depletion and open magnetic field topology inside the flux rope reveal important three-dimensional effects. There was also evidence for nonthermal elec...

Magnetic reconnection is the key process of plasma transport in the Earth's magnetotail. The X-line where magnetic field lines reconnect often moves away from the Earth. However, the precise cause of the X-line motion remains unclear. Here we present data from five THEMIS probes positioned along the Sun-Earth line and show that a tailward retreat m...

We perform a systematic study of the effect of inflow density on reconnection diffusion regions using a 2.5-D particle-in-cell code. The diffusion region structures are analyzed at times when all simulations have reconnected the same amount of magnetic flux. We find that reducing the inflow density from 1 to 1/100th of the current sheet density dra...

We report in-situ measurements by three THEMIS spacecraft showing the evolution of reconnection in a solar wind current sheet as the current sheet transited from the solar wind across the bow shock and close to the magnetopause on July 11, 2008. The observations suggest that the solar wind reconnection exhaust within the current sheet was disrupted...

In the Earth's magnetotail, it is postulated that the lobe density could be two orders of magnitude less than the plasma sheet density [e,g., Haaland et al., 2009]. However, the lobe density is never measured due to instrument limitations. In this paper, we study reconnection characteristics for varying inflow densities using a particle-in-cell (PI...

Magnetic reconnection plays a key role in the circulation of plasma through the Earth's magnetosphere. As such, the Earth's magnetotail is an excellent natural laboratory for the study of reconnection and in particular the diffusion region. To address important questions concerning observational occurrence rates and average properties, the Cluster...

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1] We present a candidate mechanism for the energization of super‐thermal electrons during magnetic reconnection in the Earth's magnetotail. By analyzing in‐situ measurements of electron distribution functions we characterize the relative energy gain of the electrons as a function of energy, DE(E). For all the events considered the high energy part...

More than 490 elliptical aerobraking and science phasing orbits made by Mars Global Surveyor (MGS) in 1997 and 1998 provide unprecedented coverage of the solar wind in the vicinity of the orbits of the martian moons Phobos and Deimos. We have performed a comprehensive survey of magnetic field perturbations in the solar wind to search for possible s...

We present a case study of ionospheric and magnetospheric response to a prolonged interval of strongly northward IMF along with enhanced solar wind dynamic pressure on November 9, 2004. Comprehensive space and ground based observations are examined to investigate global electrodynamic properties of the ionosphere and magnetosphere under northward I...

We will present burst-mode observations by the THEMIS spacecraft at the dayside magnetopause and boundary layer. During its Dayside Phase, the THEMIS burst-mode is triggered by the encounter of the magnetopause, and full 3-D ion and distributions at 3-s resolution are transmitted to the ground. The high-resolution electron measurements allow the un...

We present Mars Global Surveyor measurements of bipolar out-of-plane magnetic fields at current sheets in Mars' magnetosphere. These signatures match predictions from simulations and terrestrial observations of collisionless magnetic reconnection, and could similarly indicate differential ion and electron motion and the resulting Hall current syste...

In a recent case study, Borg et al. (2007) reported that an inverted V structure, caused by a field-aligned potential drop of 30 kV producing very strong X-ray aurora, was found in connection with tail reconnection. However, the in situ particle measurements indicated clearly that the particles responsible for the X-ray aurora were not accelerated...

1] A layer of nearly stagnant cold dense plasma is observed by THEMIS spacecraft in a closed field region immediately inside the dayside magnetopause near the low-latitude boundary layer on 3 June 2007. Using the OpenGGCM global MHD magnetosphere numerical model, we successfully reproduce this observed cold dense plasma layer in the simulation. The...

1] A previous analysis of electron distributions measured in situ by the Wind spacecraft has revealed that electrons were trapped in the electromagnetic geometry of the reconnection event encountered in the deep magnetotail. In this paper we develop a detailed theory that can account for the main anisotropic features of the electron distributions a...

The recent discovery of reconnection in solar wind current sheets has provided an unprecedented opportunity to study the structure and dynamics of reconnection without the complex boundary conditions often found in the Earth's magnetosphere. Studies of solar wind reconnection exhausts have revealed clear evidence for component reconnection with mag...

THEMIS burst mode observations of the onset of reconnection and flux rope (secondary island) formation in the magnetotail are presented and analyzed. The burst mode observations show in new detail the substructure of the reconnection generated secondary island, including large electric field fluctuations and density variations. The D structure of t...

NASA has provided several opportunities to apply for funding of education and outreach programs. One such opportunity was as a supplement to successful scientific proposed efforts under the ROSES program. NASA funded our institutional E/PO program as a supplement to a combination of three scientists' grants in the fields of Earth's magnetosphere an...

The wide range of sizes of lunar surface magnetic fields allow the study of the transition from kinetic to fluid phenomena, and the decoupling of ions and then electrons from the magnetic fields as the ambient plasmas interact with surface fields.

1] On 2007-06-03 the five THEMIS spacecraft consecutively traversed the dayside (13.5 MLT) magnetopause during northward IMF with strong B y . While one spacecraft monitored the magnetosheath, the other four encountered an extended region of nearly-stagnant magnetosheath plasma attached to the magnetopause on closed field lines. This region was muc...

1] We report observations made by the Wind spacecraft in the distant magnetotail on 22–24 October 2003 when the interplanetary magnetic field (IMF) was strongly northward for more than 32 h. A well-defined magnetotail was observed down to at least X GSM = À125 R E even after 32 h of strongly northward IMF conditions. However, the observed tail prop...

(1) Using data from Mars Global Surveyor (MGS) in combination with Particle-In-Cell (PIC) simulations of reconnection, we present the first direct evidence of collisionless magnetic reconnection at Mars. The evidence indicates that the spacecraft passed through the diffusion region where reconnection is initiated and observed the magnetic field sig...

In a recent case study based on the combined Cluster and Polar PIXIE data we reported that an inverted-V structure caused by a field aligned potential drop of 30 kV producing very strong X-ray aurora was found in connection with tail reconnection. However, the insitu particle measurements by Cluster indicate clearly that the particles responsible f...

On June 3, 2007 the five THEMIS spacecraft traversed the dayside post-noon magnetosphere like pearls on a string in a near-equatorial orbit with a 15.4 RE apogee. The leading (probe B) and trailing (probe A) spacecraft were separated by ~~3 RE. While THEMIS B monitored the magnetosheath THEMIS A, C, D, and E were still located inside the magnetosph...

We report Cluster spacecraft 1 observations of a reconnection exhaust embedded in the magnetosheath flow. The reconnection evidence consists of (1) accelerated plasma outflows, (2) interpenetrating ion beams, (3) reconnection inflows and (4) the associated tangential reconnection electric field. Furthermore, Hall magnetic fields were observed with...

1] We present simultaneous Cluster and Polar X-ray and UVI observations on 2 October 2002, when Cluster observed a magnetic reconnection diffusion region at Xgse = À16.6 Re. At the same time a bright auroral feature appeared at the footpoint of the magnetic field line connecting the ionosphere and the diffusion region. However, we found that the el...

Magnetic reconnection occurs in current sheets separating plasmas with different magnetic field orientations. Signatures of collisionless reconnection have been reported in the Earth's magnetosphere as well as in the solar wind current sheets. In some solar wind reconnection events, the X-line extends to millions of kilometers (or tens of thousands...

We report a fortuitous two-spacecraft conjunction when Geotail and Wind observed the occurrence of reconnection simultaneously at the subsolar and dawn tail flank magnetopause during stable By dominated IMF. Furthermore, bi-directional jets were observed by Geotail which indicate the presence of an X-line in the subsolar region. These observations...

We have surveyed field-aligned electrons at the lobe/plasma sheet boundary and their association with reconnection in the distant magnetotail where reconnection is quasi-steady and large scale. Asymmetric (in energy) counterstreaming electrons are detected in ~30% of the boundary crossings when high-speed flows are present in the plasma sheet. In 9...

Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Freq...

A unique 32 hour interval of very northward Interplanetary Magnetic Field (IMF) on October 22-24, 2003 created a exceptionally thick cold dense magnetotail plasma sheet, a small polar cap and accompanying small tail lobe. These features were detected by the Cluster DMSP and FAST spacecraft and modeled by a global simulation as described in papers b...

We present Cluster data and results from an OpenGGCM simulation study for an interval of more than 30 hours of nearly due northward IMF. Cluster, which is located in the near-Earth plasma sheet, observes a 3 hour long gradual transition from a hot tenuous plasma sheet (HTPS) to a cold dense plasma sheet (CDPS). The simulation shows a very good agre...

Magnetic reconnection in a current sheet is a magnetic to particle energy conversion process that is important in many space and astrophysical contexts. It is not presently known whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Here we report Wind, A...