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Khotyaintsev, Yuri V.ORCID iD iconorcid.org/0000-0001-5550-3113
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Publications (10 of 169) Show all publications
Khotyaintsev, Y. V., Graham, D. B., Norgren, C. & Vaivads, A. (2019). Collisionless Magnetic Reconnection and Waves: Progress Review. FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, 6, Article ID 70.
Open this publication in new window or tab >>Collisionless Magnetic Reconnection and Waves: Progress Review
2019 (English)In: FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, ISSN 2296-987X, Vol. 6, article id 70Article, review/survey (Refereed) Published
Abstract [en]

Magnetic reconnection is a fundamental process whereby microscopic plasma processes cause macroscopic changes in magnetic field topology, leading to explosive energy release. Waves and turbulence generated during the reconnection process can produce particle diffusion and anomalous resistivity, as well as heat the plasma and accelerate plasma particles, all of which can impact the reconnection process. We review progress on waves related to reconnection achieved using high resolution multi-point in situ observations over the last decade, since early Cluster and THEMIS observations and ending with recent Magnetospheric Multiscale results. In particular, we focus on the waves most frequently observed in relation to reconnection, ranging from low-frequency kinetic Alfven waves (KAW), to intermediate frequency lower hybrid and whistler-mode waves, electrostatic broadband and solitary waves, as well as the high-frequency upper hybrid, Langmuir, and electron Bernstein waves. Significant progress has been made in understanding localization of the different wave modes in the context of the reconnection picture, better quantification of generation mechanisms and wave-particle interactions, including anomalous resistivity. Examples include: temperature anisotropy driven whistlers in the flux pileup region, anomalous effects due to lower-hybrid waves, upper hybrid wave generation within the electron diffusion region, wave-particle interaction of electrostatic solitary waves. While being clearly identified in observations, some of the wave processes remain challenging for reconnection simulations (electron Bernstein, upper hybrid, Langmuir, whistler), as the instabilities (streaming, loss-cone, shell) which drive these waves require high resolution of distribution functions in phase space, and realistic ratio of Debye to electron inertia scales. We discuss how reconnection configuration, i.e., symmetric vs. asymmetric, guide-field vs. antiparallel, affect wave occurrence, generation, effect on particles, and feedback on the overall reconnection process. Finally, we outline some of the major open questions, such as generation of electromagnetic radiation by reconnection sites and role of waves in triggering/onset of reconnection.

Keywords
magnetic reconnection, turbulence, waves, instabilities, kinetic plasma processes
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-399975 (URN)10.3389/fspas.2019.00070 (DOI)000499869100001 ()
Funder
Swedish National Space Board, 128/17Swedish Research Council, 2016-05507
Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2019-12-17Bibliographically approved
Tang, B.-B. -., Li, W., Graham, D. B., Rager, A. C., Wang, C., Khotyaintsev, Y. V. V., . . . Burch, J. L. (2019). Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations. Geophysical Research Letters, 46(6), 3024-3032
Open this publication in new window or tab >>Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 6, p. 3024-3032Article in journal (Refereed) Published
Abstract [en]

Crescent‐shaped electron distributions perpendicular to the magnetic field are an important indicator of the electron diffusion region in magnetic reconnection. They can be formed by the electron finite gyroradius effect at plasma boundaries or by demagnetized electron motion. In this study, we present Magnetospheric Multiscale mission observations of electron crescents at the flank magnetopause on 20 September 2017, where reconnection signatures are not observed. These agyrotropic electron distributions are generated by electron gyromotion at the thin electron‐scale magnetic boundaries of a magnetic minimum after magnetic curvature scattering. The variation of their angular range in the perpendicular plane is in good agreement with predictions. Upper hybrid waves are observed to accompany the electron crescents at all four Magnetospheric Multiscale spacecraft as a result of the beam‐plasma instability associated with these agyrotropic electron distributions. This study suggests electron crescents can be more frequently formed at the magnetopause.

Abstract [en]

Plain Language Summary

In this study, we present Magnetospheric Multiscale mission observations of electron crescents at the flank magnetopause and these agyrotropic electron distributions are formed at thin electron‐scale magnetic boundaries after electron pitch angle scattering by the curved magnetic field. These results suggest that agyrotropic electron distributions can be more frequently formed at the magnetopause: (1) magnetic reconnection is not necessary, although electron crescents are taken as one of the observational signatures of the electron diffusion region, and (2) agyrotropic electron distributions can cover a large local time range to the flank magnetopause. In addition, upper hybrid waves accompanied with the electron crescents are observed as a result of the beam‐plasma interaction associated with these agyrotropic electron distributions. This suggests that high‐frequency waves play a role in electron dynamics through wave‐particle interactions.

Keywords
agyrotropic electron distributions, electron finite gyroradius effect, upper hybrid waves
National Category
Fusion, Plasma and Space Physics Geophysics
Identifiers
urn:nbn:se:uu:diva-382993 (URN)10.1029/2019GL082231 (DOI)000464650400002 ()
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-12-11Bibliographically approved
Hanson, E. L., Agapitov, O. V., Mozer, F. S., Krasnoselskikh, V., Bale, S. D., Avanov, L., . . . Giles, B. (2019). Cross-Shock Potential in Rippled Versus Planar Quasi-Perpendicular Shocks Observed by MMS. Geophysical Research Letters, 46(5), 2381-2389
Open this publication in new window or tab >>Cross-Shock Potential in Rippled Versus Planar Quasi-Perpendicular Shocks Observed by MMS
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 5, p. 2381-2389Article in journal (Refereed) Published
Abstract [en]

The unprecedented detail of measurements by the four Magnetospheric Multiscale (MMS) spacecraft enable deeper investigation of quasi-perpendicular collisionless shocks. We compare shock normals, planarities, and Normal Incidence Frame cross-shock potentials determined from electric field measurements and proxies, for a subcritical interplanetary shock and a supercritical bow shock. The subcritical shock's cross-shock potential was 26 +/- 6 V. The shock scale was 33 km, too short to allow comparison with proxies from ion moments. Proxies from electron moments provided potential estimates of 40 +/- 5 V. Shock normals from magnetic field minimum variance analysis were nearly identical, indicating a planar front. The supercritical shock's cross-shock potential was estimated to be from 290 to 440 V from the different spacecraft measurements, with shock scale 120 km. Reflected ions contaminated the ion-based proxies upstream, whereas electron-based proxies yielded reasonable estimates of 250 +/- 50 V. Shock normals from electric field maximum variance analysis differed, indicating a rippled front. Plain Language Summary An important problem in shock physics is understanding how the incoming plasma flow is thermalized across the shock. The role of the cross-shock electric field has not been well studied. We compare measurements and implicit estimates of cross-shock potential for a quasi-perpendicular weak (low Mach) shock and a quasi-perpendicular strong (moderate/high Mach) shock using data from the four Magnetospheric Multiscale satellites. The weak shock had lower cross-shock potential in the Normal Incidence Frame (about 30 V) than the strong shock (about 300 V). We also estimated the potential deduced from ion and electron data. Electron-based estimates agreed reasonably well with the measurements, but ion-based estimates encountered problems. The weak shock was too short compared to the ion data sampling period, while the strong shock reflected ions back into the upstream flow. Data from individual spacecraft indicated that the surface of the strong shock was not flat but rippled, one reason why its measured potential showed such a broad range.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
solar wind, cross-shock potential, electric field measurements, interplanetary shock, bow shock, rippled shocks
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-381589 (URN)10.1029/2018GL080240 (DOI)000462612900007 ()
Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-12Bibliographically approved
Dimmock, A. P., Russell, C. T., Sagdeev, R. Z., Krasnoselskikh, V., Walker, S. N., Carr, C., . . . Balikhin, M. A. (2019). Direct evidence of nonstationary collisionless shocks in space plasmas. Science Advances, 5(2), Article ID eaau9926.
Open this publication in new window or tab >>Direct evidence of nonstationary collisionless shocks in space plasmas
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2019 (English)In: Science Advances, E-ISSN 2375-2548, Vol. 5, no 2, article id eaau9926Article in journal (Refereed) Published
Abstract [en]

Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.

Place, publisher, year, edition, pages
AMER ASSOC ADVANCEMENT SCIENCE, 2019
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-379771 (URN)10.1126/sciadv.aau9926 (DOI)000460145700047 ()30820454 (PubMedID)
Funder
Swedish Research Council, 2016-05507Academy of Finland, 288472 267073/2013Swedish Civil Contingencies Agency, 2016-2102
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-21Bibliographically approved
He, J., Duan, D., Wang, T., Zhu, X., Li, W., Verscharen, D., . . . Burch, J. (2019). Direct Measurement of the Dissipation Rate Spectrum around Ion Kinetic Scales in Space Plasma Turbulence. Astrophysical Journal, 880(2), Article ID 121.
Open this publication in new window or tab >>Direct Measurement of the Dissipation Rate Spectrum around Ion Kinetic Scales in Space Plasma Turbulence
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2019 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 880, no 2, article id 121Article in journal (Refereed) Published
Abstract [en]

The energy of turbulence in the universe, which cascades from large fluid scales to small kinetic scales, is believed to be dissipated through conversion to thermal or nonthermal kinetic energy. However, identifying the dissipation processes and measuring the dissipation rate in turbulence remain challenging. Based on unprecedented high-quality measurements of space plasma turbulence by the Magnetospheric Multiscale mission, we propose a novel approach to measure the scale-dependent spectrum of the energy conversion rate between the fluctuating electromagnetic energy and plasma kinetic energy. The energy conversion rate spectrum is found to show a positive bulge around the ion kinetic scale, which clearly indicates the dissipation of the turbulent energy. The energy dissipation rate around the ion scale is estimated to be 0.5 x 10(6) J kg(-1) s(-1). This work provides basic information on local dissipation in magnetosheath turbulence and sets up a new paradigm for studying the dissipation of universal plasma turbulence.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
plasmas, turbulence, waves
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-393340 (URN)10.3847/1538-4357/ab2a79 (DOI)000479029300003 ()
Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically approved
Chen, L.-J. -., Wang, S., Hesse, M., Ergun, R. E., Moore, T., Giles, B., . . . Lindqvist, P.-A. -. (2019). Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields. Geophysical Research Letters, 46(12), 6230-6238
Open this publication in new window or tab >>Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6230-6238Article in journal (Refereed) Published
Abstract [en]

Kinetic structures of electron diffusion regions (EDRs) under finite guide fields in magnetotail reconnection are reported. The EDRs with guide fields 0.14-0.5 (in unit of the reconnecting component) are detected by the Magnetospheric Multiscale spacecraft. The key new features include the following: (1) cold inflowing electrons accelerated along the guide field and demagnetized at the magnetic field minimum while remaining a coherent population with a low perpendicular temperature, (2) wave fluctuations generating strong perpendicular electron flows followed by alternating parallel flows inside the reconnecting current sheet under an intermediate guide field, and (3) gyrophase bunched electrons with high parallel speeds leaving the X-line region. The normalized reconnection rates for the three EDRs range from 0.05 to 0.3. The measurements reveal that finite guide fields introduce new mechanisms to break the electron frozen-in condition. Plain Language Summary Magnetic reconnection plays a crucial role in the dynamics of the terrestrial magnetotail. For reconnection to occur, the plasma must decouple from the magnetic field. The bounce motion of particles in the magnetotail current sheet is regarded as a key to this decoupling for cases when the current sheet has no magnetic field along the direction of the current. This paper reports that while bounce motion remains relevant when a finite magnetic field is present along the current, new mechanisms to decouple electrons from the magnetic field are introduced, and new open questions unfold. The observations are based on measurements from the Magnetospheric Multiscale mission. The mission's unprecedented high cadence electron data make possible the revelation of the new mechanisms. The results reported in this paper expand the frontiers of our knowledge on magnetotail reconnection and have major implications on the fundamental physics of magnetic reconnection in all plasma systems where binary collisions are not effective, including solar, astrophysical, and laboratory plasmas. Rapid dissemination of the results will set the ground for advances in magnetic reconnection research.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-392877 (URN)10.1029/2019GL082393 (DOI)000477616300009 ()
Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-09-26Bibliographically approved
Hwang, K.-J. -., Choi, E., Dokgo, K., Burch, J. L., Sibeck, D. G., Giles, B. L., . . . Strangeway, R. J. (2019). Electron Vorticity Indicative of the Electron Diffusion Region of Magnetic Reconnection. Geophysical Research Letters, 46(12), 6287-6296
Open this publication in new window or tab >>Electron Vorticity Indicative of the Electron Diffusion Region of Magnetic Reconnection
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6287-6296Article in journal (Refereed) Published
Abstract [en]

While vorticity defined as the curl of the velocity has been broadly used in fluid and plasma physics, this quantity has been underutilized in space physics due to low time resolution observations. We report Magnetospheric Multiscale (MMS) observations of enhanced electron vorticity in the vicinity of the electron diffusion region of magnetic reconnection. On 11 July 2017 MMS traversed the magnetotail current sheet, observing tailward-to-earthward outflow reversal, current-carrying electron jets in the direction along the electron meandering motion or out-of-plane direction, agyrotropic electron distribution functions, and dissipative signatures. At the edge of the electron jets, the electron vorticity increased with magnitudes greater than the electron gyrofrequency. The out-of-plane velocity shear along distance from the current sheet leads to the enhanced vorticity. This, in turn, contributes to the magnetic field perturbations observed by MMS. These observations indicate that electron vorticity can act as a proxy for delineating the electron diffusion region of magnetic reconnection.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
magnetic reconnection, electron diffusion region, electron vorticity, reconnection, magnetotail, current sheet
National Category
Astronomy, Astrophysics and Cosmology Geophysics
Identifiers
urn:nbn:se:uu:diva-392880 (URN)10.1029/2019GL082710 (DOI)000477616300015 ()
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24Bibliographically approved
Chen, Z. Z., Fu, H. S., Liu, C. M., Wang, T. Y., Ergun, R. E., Cozzani, G., . . . Burch, J. L. (2019). Electron-Driven Dissipation in a Tailward Flow Burst. Geophysical Research Letters, 46(11), 5698-5706
Open this publication in new window or tab >>Electron-Driven Dissipation in a Tailward Flow Burst
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 11, p. 5698-5706Article in journal (Refereed) Published
Abstract [en]

Traditionally, the magnetotail flow burst outside the diffusion region is known to carry ions and electrons together (V-i = V-e), with the frozen-in condition well satisfied (E + V-e x B = 0). Such picture, however, may not be true, based on our analyses of the high-resolution MMS (Magnetospheric Multiscale mission) data. We find that inside the flow burst the electrons and ions can be decoupled (V-e not equal V-i), with the electron speed 5 times larger than the ion speed. Such super-Alfvenic electron jet, having scale of 10 d(i) (ion inertial length) in X-GSM direction, is associated with electron demagnetization (E + V-e x B not equal 0), electron agyrotropy (crescent distribution), and O-line magnetic topology but not associated with the flow reversal and X-line topology; it can cause strong energy dissipation and electron heating. We quantitatively analyze the dissipation and find that it is primarily attributed to lower hybrid drift waves. These results emphasize the non-MHD (magnetohydrodynamics) behaviors of magnetotail flow bursts and the role of lower hybrid drift waves in dissipating energies.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
magnetotail flow burst, non-MHD behaviors, energy dissipation, lower hybrid drift wave, O-line topology
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-392883 (URN)10.1029/2019GL082503 (DOI)000477616200008 ()
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24Bibliographically approved
Zhou, M., Huang, J., Man, H. Y., Deng, X. H., Zhong, Z. H., Russell, C. T., . . . Burch, J. L. (2019). Electron-scale Vertical Current Sheets in a Bursty Bulk Flow in the Terrestrial Magnetotail. Astrophysical Journal Letters, 872(2), Article ID L26.
Open this publication in new window or tab >>Electron-scale Vertical Current Sheets in a Bursty Bulk Flow in the Terrestrial Magnetotail
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2019 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 872, no 2, article id L26Article in journal (Refereed) Published
Abstract [en]

We report Magnetospheric Multiscale observations of multiple vertical current sheets (CSs) in a bursty bulk flow in the near-Earth magnetotail. Two of the CSs were fine structures of a dipolarization front (DF) at the leading edge of the flow. The other CSs were a few Earth radii tailward of the DF; that is, in the wake of the DF. Some of these vertical CSs were a few electron inertial lengths thick and were converting energy from magnetic field to plasma. The currents of the CSs in the DF wake were carried by electrons that formed flow shear layers. These electron-scale CSs were probably formed during the turbulent evolution of the bursty bulk flow and are important for energy conversion associated with fast flows.

Keywords
magnetic fields, magnetic reconnection, turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-378980 (URN)10.3847/2041-8213/ab0424 (DOI)000459254000007 ()
Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Voros, Z., Yordanova, E., Khotyaintsev, Y. V., Varsani, A. & Narita, Y. (2019). Energy Conversion at Kinetic Scales in the Turbulent Magnetosheath. FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, 6, Article ID 60.
Open this publication in new window or tab >>Energy Conversion at Kinetic Scales in the Turbulent Magnetosheath
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2019 (English)In: FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, ISSN 2296-987X, Vol. 6, article id 60Article in journal (Refereed) Published
Abstract [en]

The process of conversion or dissipation of energy in nearly collisionless turbulent space plasma, is yet to be fully understood. The existing models offer different energy dissipation mechanisms which are based on wave particle interactions or non-resonant stochastic heating. There are other mechanisms of irreversible processes in space. For example, turbulence generated coherent structures, e.g., current sheets are ubiquitous in the solar wind and quasi-parallel magnetosheath. Reconnecting current sheets in plasma turbulence are converting magnetic energy to kinetic and thermal energy. It is important to understand how the multiple (reconnecting) current sheets contribute to spatial distribution of turbulent dissipation. However, detailed studies of such complex structures have been possible mainly via event studies in proper coordinate systems, in which the local inflow/outflow, electric and magnetic field directions, and gradients could be studied. Here we statistically investigate different energy exchange/dissipation (EED) measures defined in local magnetic field-aligned coordinates, as well as frame-independent scalars. The presented statistical comparisons based on the unique high-resolution MMS data contribute to better understanding of the plasma heating problem in turbulent space plasmas.

Keywords
plasma turbulence, current sheets, magnetic reconnection, terrestrial magnetosheath, plasma heating
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-394953 (URN)10.3389/fspas.2019.00060 (DOI)000485744300001 ()
Funder
Swedish Civil Contingencies Agency, 2016-2102
Available from: 2019-10-21 Created: 2019-10-21 Last updated: 2019-11-22Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5550-3113

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