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Fu, H. S., Vaivads, A., Khotyaintsev, Y. V., André, M., Cao, J. B., Olshevsky, V., . . . Retino, A. (2017). Intermittent energy dissipation by turbulent reconnection. Geophysical Research Letters, 44(1), 37-43
Open this publication in new window or tab >>Intermittent energy dissipation by turbulent reconnection
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 1, p. 37-43Article in journal (Refereed) Published
Abstract [en]

Magnetic reconnectionthe process responsible for many explosive phenomena in both nature and laboratoryis efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multipoint measurements of the diffusion region at the sub-ion scale. Here we report such a measurement by Clusterfour spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased and the energy dissipation, Ej, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
Keywords
turbulent reconnection, energy dissipation, turbulence, magnetic nulls, current filaments, intermittence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253251 (URN)10.1002/2016GL071787 (DOI)000393954900005 ()2-s2.0-85010638265 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20190625

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-25Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Vaivads, A. & Andre, M. (2016). Electrostatic solitary waves and electrostatic waves at the magnetopause. Journal of Geophysical Research - Space Physics, 121(4), 3069-3092
Open this publication in new window or tab >>Electrostatic solitary waves and electrostatic waves at the magnetopause
2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 4, p. 3069-3092Article in journal (Refereed) Published
Abstract [en]

Electrostatic solitary waves (ESWs) are characterized by localized bipolar electric fields parallel to the magnetic field and are frequently observed in space plasmas. In this paper a study of ESWs and field-aligned electrostatic waves, which do not exhibit localized bipolar fields, near the magnetopause is presented using the Cluster spacecraft. The speeds, length scales, field strengths, and potentials are calculated and compared with the local plasma conditions. A large range of speeds is observed, suggesting different generation mechanisms. In contrast, a smaller range of length scales normalized to the Debye length lambda(D) is found. For ESWs the average length between the positive and negative peak fields is 9 lambda(D), comparable to the average half wavelength of electrostatic waves. Statistically, the lengths and speeds of ESWs and electrostatic waves are shown to be similar. The length scales and potentials of the ESWs are consistent with predictions for stable electron holes. The maximum ESW potentials are shown to be constrained by the length scale and the magnetic field strength at the magnetopause and in the magnetosheath. The observed waves are consistent with those generated by the warm bistreaming instability, beam-plasma instability, and electron-ion instabilities, which account for the observed speeds and length scales. The large range of wave speeds suggests that the waves can couple different electron populations and electrons with ions, heating the plasma and contributing to anomalous resistivity.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253470 (URN)10.1002/2015JA021527 (DOI)000379960300018 ()
Funder
Swedish National Space Board, 128/11:2 77/13
Note

QC 20190624

Available from: 2019-06-15 Created: 2019-06-15 Last updated: 2019-06-24Bibliographically approved
Fu, H. S., Cao, J. B., Vaivads, A., Khotyaintsev, Y. V., Andre, M., Dunlop, M., . . . Eriksson, E. (2016). Identifying magnetic reconnection events using the FOTE method. Journal of Geophysical Research - Space Physics, 121(2), 1263-1272
Open this publication in new window or tab >>Identifying magnetic reconnection events using the FOTE method
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2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 2, p. 1263-1272Article in journal (Refereed) Published
Abstract [en]

A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission. ion

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2016
Keywords
magnetic reconnection, MMS mission, FOTE method, magnetic null, X line, O line
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253248 (URN)10.1002/2015JA021701 (DOI)000373002100023 ()2-s2.0-84975698091 (Scopus ID)
Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-25Bibliographically approved
Li, W., Andre, M., Khotyaintsev, Y. V., Vaivads, A., Graham, D. B., Toledo-Redondo, S., . . . Strangeway, R. J. (2016). Kinetic evidence of magnetic reconnection due to Kelvin-Helmholtz waves. Geophysical Research Letters, 43(11), 5635-5643
Open this publication in new window or tab >>Kinetic evidence of magnetic reconnection due to Kelvin-Helmholtz waves
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 11, p. 5635-5643Article in journal (Refereed) Published
Abstract [en]

The Kelvin-Helmholtz (KH) instability at the Earth's magnetopause is predominantly excited during northward interplanetary magnetic field (IMF). Magnetic reconnection due to KH waves has been suggested as one of the mechanisms to transfer solar wind plasma into the magnetosphere. We investigate KH waves observed at the magnetopause by the Magnetospheric Multiscale (MMS) mission; in particular, we study the trailing edges of KH waves with Alfvenic ion jets. We observe gradual mixing of magnetospheric and magnetosheath ions at the boundary layer. The magnetospheric electrons with energy up to 80keV are observed on the magnetosheath side of the jets, which indicates that they escape into the magnetosheath through reconnected magnetic field lines. At the same time, the low-energy (below 100eV) magnetosheath electrons enter the magnetosphere and are heated in the field-aligned direction at the high-density edge of the jets. Our observations provide unambiguous kinetic evidence for ongoing reconnection due to KH waves.

Place, publisher, year, edition, pages
Blackwell Publishing, 2016
Keywords
kinetic evidence, reconnection, Kelvin-Helmholtz wave
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253541 (URN)10.1002/2016GL069192 (DOI)000379851800012 ()2-s2.0-84977100261 (Scopus ID)
Funder
Swedish National Space Board, 164/14, 176/15
Note

QC 20190625

Available from: 2019-06-15 Created: 2019-06-15 Last updated: 2019-06-25Bibliographically approved
Bale, S. D., Goetz, K., Harvey, P. R., Turin, P., Bonnell, J. W., Dudok de Wit, T., . . . Wygant, J. R. (2016). The FIELDS Instrument Suite for Solar Probe Plus. Space Science Reviews, 204(1-4), 49-82
Open this publication in new window or tab >>The FIELDS Instrument Suite for Solar Probe Plus
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2016 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 204, no 1-4, p. 49-82Article, review/survey (Refereed) Published
Abstract [en]

NASA's Solar Probe Plus (SPP) mission will make the first in situ measurements of the solar corona and the birthplace of the solar wind. The FIELDS instrument suite on SPP will make direct measurements of electric and magnetic fields, the properties of in situ plasma waves, electron density and temperature profiles, and interplanetary radio emissions, amongst other things. Here, we describe the scientific objectives targeted by the SPP/FIELDS instrument, the instrument design itself, and the instrument concept of operations and planned data products.

Keywords
Coronal heating, Solar Probe Plus
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253221 (URN)10.1007/s11214-016-0244-5 (DOI)000390050700003 ()
Note

QC 20190624

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-24Bibliographically approved
Huang, S. Y., Fu, H. S., Vaivads, A., Yuan, Z. G., Pang, Y., Zhou, M., . . . Wang, D. D. (2015). Dawn-dusk scale of dipolarization front in the Earth's magnetotail: multi-cases study. Astrophysics and Space Science, 357(1), Article ID 22.
Open this publication in new window or tab >>Dawn-dusk scale of dipolarization front in the Earth's magnetotail: multi-cases study
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2015 (English)In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 357, no 1, article id 22Article in journal (Refereed) Published
Abstract [en]

We analyze three dipolarization front (DF) events to investigate their dawn-dusk scales in the Earth's magnetotail using the Cluster measurements in year 2007, when the spacecraft separation is about 1.8 Re (Re is the Earth's radius) and is appropriate for investigating the DF scale. Based on the Minimum Variance Analysis (MVA) and the general shape of the DF, we found that Cluster detected the center and the flank (or just beyond the flank) of DF in the same event. This means that the scale of DF is about 3.6 Re in the dawn-dusk direction, larger than that reported in previous studies. Using the semicircle function to fit the observations, we got the dawn-dusk scale of similar to 3.2-3.6 Re, consistent with the rough estimation. Considering large separation among the spacecraft, the timing analysis cannot be used to obtain the normal of DF and the propagation velocity along the normal. One should be careful when performing timing analysis of DF using the Cluster data, and have to carry on MVA analysis to check the normal of DF before do timing analysis.

Place, publisher, year, edition, pages
Kluwer Academic Publishers, 2015
Keywords
Magnetotail, Dipolarization front, Dawn-dusk scale, Timing analysis
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253487 (URN)10.1007/s10509-015-2298-3 (DOI)000352850400022 ()2-s2.0-84928243422 (Scopus ID)
Note

QC 20190625

Available from: 2019-06-15 Created: 2019-06-15 Last updated: 2019-06-25Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V., Vaivads, A. & André, M. (2015). Electrostatic solitary waves with distinct speeds associated with asymmetric reconnection. Geophysical Research Letters, 42(2), 215-224
Open this publication in new window or tab >>Electrostatic solitary waves with distinct speeds associated with asymmetric reconnection
2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 2, p. 215-224Article in journal (Refereed) Published
Abstract [en]

Electrostatic solitary waves (ESWs) are observed at the magnetopause with distinct time scales. These ESWs are associated with asymmetric reconnection of the cold dense magnetosheath plasma with the hot tenuous magnetospheric plasma. The distinct time scales are shown to be due to ESWs moving at distinct speeds and having distinct length scales. The length scales are of order 5-50 Debye lengths, and the speeds range from approximate to 50 km s(-1) to approximate to 1000 km s(-1). The ESWs are observed near the reconnection separatrices. The observation of ESWs with distinct speeds suggests that multiple instabilities are occurring. The implications for reconnection at the magnetopause are discussed.

Keywords
electron solitary waves, magnetic reconnection, magnetopause
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-253471 (URN)10.1002/2014GL062538 (DOI)000349956000005 ()
Note

QC 20190624

Available from: 2019-06-15 Created: 2019-06-15 Last updated: 2019-06-24Bibliographically approved
Fu, H. S., Vaivads, A., Khotyaintsev, Y. V., Olshevsky, V., André, M., Cao, J. B., . . . Lapenta, G. (2015). How to find magnetic nulls and reconstruct field topology with MMS data?. Journal of Geophysical Research - Space Physics, 120(5), 3758-3782
Open this publication in new window or tab >>How to find magnetic nulls and reconstruct field topology with MMS data?
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2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 5, p. 3758-3782Article in journal (Refereed) Published
Abstract [en]

In this study, we apply a new method-the first-order Taylor expansion (FOTE)-to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forthcoming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3-D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2-D (X and O); (3) reconstruct the magnetic field topology. We quantitatively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology by using the data from 3-D kinetic simulations. The influences of SC separation (0.05 similar to 1 d(i)) and null-SC distance (0 similar to 1 d(i)) on the accuracy are both considered. We find that (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 d(i), and the null-SC distance is smaller than 0.25 similar to 0.5 d(i); (2) for a null pair, the accuracy is same as in the isolated-null situation, except at the separator line, where the field is nonlinear. We define a parameter xi vertical bar(lambda(1) +lambda(2) +lambda(3))vertical bar/vertical bar lambda vertical bar(max) in terms of the eigenvalues (lambda(i)) of the null to quantify the quality of our method-the smaller this parameter the better the results. Comparing to the previously used parameter (eta vertical bar del center dot B vertical bar/vertical bar del x B vertical bar), xi is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and the forthcoming MMS mission. For the MMS mission, this null-finding algorithm can be used to trigger its burst-mode measurements.

Place, publisher, year, edition, pages
2000 Florida Ave NW Washington, DC 20009, USA: American Geophysical Union (AGU), 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-253252 (URN)10.1002/2015JA021082 (DOI)000357869600035 ()2-s2.0-84934989859 (Scopus ID)
Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-18Bibliographically approved
Divin, A., Khotyaintsev, Y. V., Vaivads, A. & André, M. (2015). Lower hybrid drift instability at a dipolarization front. Journal of Geophysical Research - Space Physics, 120(2), 1124-1132
Open this publication in new window or tab >>Lower hybrid drift instability at a dipolarization front
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, p. 1124-1132Article in journal (Refereed) Published
Abstract [en]

We present observations of a reconnection jet front detected by the Cluster satellites in the magnetotail of Earth, which are commonly referred to as dipolarization fronts. We investigate in detail electric field structures observed at the front which have frequency in the lower hybrid range and amplitudes reaching 40mV/m. We determine the frequency and phase velocity of these structures in the reference frame of the front and identify them as a manifestation of the lower hybrid drift instability (LHDI) excited at the sharp density gradient at the front. The LHDI is observed in the nonlinear stage of its evolution as the electrostatic potential of the structures is comparable to approximate to 10% of the electron temperature. The front appears to be a coherent structure on ion and MHD scales, suggesting existence of a dynamic equilibrium between excitation of the LHDI and recovery of the steep density gradient at the front.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2015
Keywords
magnetosphere, dipolarization front, magnetic reconnection, LHDI
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-253235 (URN)10.1002/2014JA020528 (DOI)000351360800020 ()2-s2.0-84924811272 (Scopus ID)
Note

QC 20190625

Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-25Bibliographically approved
Norgren, C., André, M., Graham, D. B. B., Khotyaintsev, Y. V. V. & Vaivads, A. (2015). Slow electron holes in multicomponent plasmas. Geophysical Research Letters, 42(18), 7264-7272
Open this publication in new window or tab >>Slow electron holes in multicomponent plasmas
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2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 18, p. 7264-7272Article in journal (Refereed) Published
Abstract [en]

Electrostatic solitary waves (ESWs), often interpreted as electron phase space holes, are commonly observed in plasmas and are manifestations of strongly nonlinear processes. Often slow ESWs are observed, suggesting generation by the Buneman instability. The instability criteria, however, are generally not satisfied. We show how slow electron holes can be generated by a modified Buneman instability in a plasma that includes a slow electron beam on top of a warm thermal electron background. This lowers the required current for marginal instability and allows for generation of slow electron holes for a wide range of beam parameters that covers expected plasma distributions in space, for example, in magnetic reconnection regions. At higher beam speeds, the electron-electron beam instability becomes dominant instead, producing faster electron holes. The range of phase speeds for this model is consistent with a statistical set of observations at the magnetopause made by Cluster.

Keywords
Multi-component plasma, Modified Buneman instability, Ion-electron instability, Slow electron holes
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-253558 (URN)10.1002/2015GL065390 (DOI)000363412400004 ()2-s2.0-84945218399 (Scopus ID)
Funder
Swedish Research Council, 23/12:2
Note

QC 20190617

Available from: 2019-06-15 Created: 2019-06-15 Last updated: 2019-06-17Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-3725-4920

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