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Zhou, M., Berchem, J., Walker, R. J., El-Alaoui, M., Deng, X., Cazzola, E., . . . Burch, J. L. (2017). Coalescence of Macroscopic Flux Ropes at the Subsolar Magnetopause: Magnetospheric Multiscale Observations. Physical Review Letters, 119(5), Article ID 055101.
Open this publication in new window or tab >>Coalescence of Macroscopic Flux Ropes at the Subsolar Magnetopause: Magnetospheric Multiscale Observations
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2017 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 5, 055101Article in journal (Refereed) Published
Abstract [en]

We report unambiguous in situ observation of the coalescence of macroscopic flux ropes by the magnetospheric multiscale (MMS) mission. Two coalescing flux ropes with sizes of similar to 1 R-E were identified at the subsolar magnetopause by the occurrence of an asymmetric quadrupolar signature in the normal component of the magnetic field measured by the MMS spacecraft. An electron diffusion region (EDR) with a width of four local electron inertial lengths was embedded within the merging current sheet. The EDR was characterized by an intense parallel electric field, significant energy dissipation, and suprathermal electrons. Although the electrons were organized by a large guide field, the small observed electron pressure nongyrotropy may be sufficient to support a significant fraction of the parallel electric field within the EDR. Since the flux ropes are observed in the exhaust region, we suggest that secondary EDRs are formed further downstream of the primary reconnection line between the magnetosheath and magnetospheric fields.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-212332 (URN)10.1103/PhysRevLett.119.055101 (DOI)000406760300013 ()2-s2.0-85026918290 (Scopus ID)
Note

QC 20170821

Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2017-11-10Bibliographically approved
Alm, L., Argall, M. R., Torbert, R. B., Farrugia, C. J., Burch, J. L., Ergun, R. E., . . . Shuster, J. (2017). EDR signatures observed by MMS in the 16 October event presented in a 2-D parametric space. Journal of Geophysical Research - Space Physics, 122(3), 3262-3276.
Open this publication in new window or tab >>EDR signatures observed by MMS in the 16 October event presented in a 2-D parametric space
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 3, 3262-3276 p.Article in journal (Refereed) Published
Abstract [en]

We present a method for mapping the position of satellites relative to the X line using the measured B-L and B-N components of the magnetic field and apply it to the Magnetospheric multiscale (MMS) encounter with the electron diffusion region (EDR) which occurred on 13:07 UT on 16 October 2015. Mapping the data to our parametric space succeeds in capturing many of the signatures associated with magnetic reconnection and the electron diffusion region. This offers a method for determining where in the reconnection region the satellites were located. In addition, parametric mapping can also be used to present data from numerical simulations. This facilitates comparing data from simulations with data from in situ observations as one can avoid the complicated process using boundary motion analysis to determine the geometry of the reconnection region. In parametric space we can identify the EDR based on the collocation of several reconnection signatures, such as electron nongyrotropy, electron demagnetization, parallel electric fields, and energy dissipation. The EDR extends 2-3km in the normal direction and in excess of 20km in the tangential direction. It is clear that the EDR occurs on the magnetospheric side of the topological X line, which is expected in asymmetric reconnection. Furthermore, we can observe a north-south asymmetry, where the EDR occurs north of the peak in out-of-plane current, which may be due to the small but finite guide field.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keyword
magnetic reconnection, electron diffusion region, MMS, parametric space, multispacecraft, asymmetric reconnection
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-206707 (URN)10.1002/2016JA023788 (DOI)000399710900030 ()2-s2.0-85016392229 (Scopus ID)
Note

QC 20170508

Available from: 2017-05-08 Created: 2017-05-08 Last updated: 2017-05-08Bibliographically approved
Chasapis, A., Matthaeus, W. H., Parashar, T. N., Lecontel, O., Retinò, A., Breuillard, H., . . . Saito, Y. (2017). Electron Heating at Kinetic Scales in Magnetosheath Turbulence. Astrophysical Journal, 836(2), Article ID 247.
Open this publication in new window or tab >>Electron Heating at Kinetic Scales in Magnetosheath Turbulence
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2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 836, no 2, 247Article in journal (Refereed) Published
Abstract [en]

We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth's magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at the edges of the current sheet.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017
Keyword
acceleration of particles, magnetic reconnection, plasmas, turbulence
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-208005 (URN)10.3847/1538-4357/836/2/247 (DOI)000401169200015 ()2-s2.0-85014247266 (Scopus ID)
Note

QC 2017-06-08

Available from: 2017-06-08 Created: 2017-06-08 Last updated: 2017-06-13Bibliographically approved
Graham, D. B., Khotyaintsev, Y. V. V., Norgren, C., Vaivads, A., Andre, M., Toledo-Redondo, S., . . . Burch, J. L. (2017). Lower hybrid waves in the ion diffusion and magnetospheric inflow regions. Journal of Geophysical Research - Space Physics, 122(1), 517-533.
Open this publication in new window or tab >>Lower hybrid waves in the ion diffusion and magnetospheric inflow regions
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 1, 517-533 p.Article in journal (Refereed) Published
Abstract [en]

The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
Keyword
Magnetic reconnection, Ion diffusion region, Lower hybrid waves
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-205170 (URN)10.1002/2016JA023572 (DOI)000395655800038 ()2-s2.0-85010693276 (Scopus ID)
Note

QC 20170411

Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-11-29Bibliographically approved
Matsui, H., Erickson, P. J., Foster, J. C., Torbert, R. B., Argall, M. R., Anderson, B. J., . . . Turner, D. L. (2016). Dipolarization in the inner magnetosphere during a geomagnetic storm on 7 October 2015. Geophysical Research Letters, 43(18), 9397-9405.
Open this publication in new window or tab >>Dipolarization in the inner magnetosphere during a geomagnetic storm on 7 October 2015
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 18, 9397-9405 p.Article in journal (Refereed) Published
Abstract [en]

A dipolarization event was observed by the Magnetospheric Multiscale (MMS) spacecraft at L = 3.8 and 19.8 magnetic local time starting at similar to 23:42:36 UT on 7 October 2015. The magnetic and electric fields showed initially coherent variations between the spacecraft. The sunward convection turned tailward after the dipolarization. The observation is interpreted in terms of the pressure balance or the momentum equation. This was followed by a region traversed where the fields were irregular. The scale length was of the order of the ion gyroradius, suggesting the kinetic nature of the fluctuations. Combination of the multi-instrument, multispacecraft data reveals a more detailed picture of the dipolarization event in the inner magnetosphere. Conjunction ionosphere-plasmasphere observations from DMSP, two-dimensional GPS total electron content, the Millstone Hill midlatitude incoherent scatter radar, and AMPERE measurements imply that MMS observations are located on the poleward edge of the ionospheric trough where Region 2 field-aligned currents flow.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2016
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:kth:diva-196421 (URN)10.1002/2016GL070677 (DOI)000385392900006 ()2-s2.0-84988640811 (Scopus ID)
Note

QC 20161128

Available from: 2016-11-28 Created: 2016-11-14 Last updated: 2017-11-29Bibliographically approved
Wilder, F. D., Ergun, R. E., Schwartz, S. J., Newman, D. L., Eriksson, S., Stawarz, J. E., . . . Magnes, W. (2016). Observations of large-amplitude, parallel, electrostatic waves associated with the Kelvin-Helmholtz instability by the magnetospheric multiscale mission. Geophysical Research Letters, 43(17), 8859-8866.
Open this publication in new window or tab >>Observations of large-amplitude, parallel, electrostatic waves associated with the Kelvin-Helmholtz instability by the magnetospheric multiscale mission
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 17, 8859-8866 p.Article in journal (Refereed) Published
Abstract [en]

On 8 September 2015, the four Magnetospheric Multiscale spacecraft encountered a Kelvin-Helmholtz unstable magnetopause near the dusk flank. The spacecraft observed periodic compressed current sheets, between which the plasma was turbulent. We present observations of large-amplitude (up to 100 mV/m) oscillations in the electric field. Because these oscillations are purely parallel to the background magnetic field, electrostatic, and below the ion plasma frequency, they are likely to be ion acoustic-like waves. These waves are observed in a turbulent plasma where multiple particle populations are intermittently mixed, including cold electrons with energies less than 10 eV. Stability analysis suggests a cold electron component is necessary for wave growth.

Place, publisher, year, edition, pages
Blackwell Publishing, 2016
Keyword
boundary layer, electrostatic waves, Kelvin-Helmholtz, turbulence, Boundary layers, Electric field effects, Electric fields, Electrostatics, Magnetosphere, Plasma turbulence, Spacecraft, Ion plasma frequency, Kelvin- helmholtz instabilities, Magnetospheric multi scale, Magnetospheric multiscale missions, Multiple particles, Stability analysis, Atmospheric thermodynamics, amplitude, electric field, Kelvin-Helmholtz instability, magnetic field, magnetopause, observational method, plasma
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-195326 (URN)10.1002/2016GL070404 (DOI)2-s2.0-84984837657 (Scopus ID)
Note

QC 20161109

Available from: 2016-11-09 Created: 2016-11-02 Last updated: 2017-11-29Bibliographically approved
Alm, L., Marklund, G. & Karlsson, T. (2015). Electron density and parallel electric field distribution of the auroral density cavity. Journal of Geophysical Research, 120(11), 9428-9441.
Open this publication in new window or tab >>Electron density and parallel electric field distribution of the auroral density cavity
2015 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 120, no 11, 9428-9441 p.Article in journal (Refereed) Published
Abstract [en]

We present an event study in which Cluster satellites C1 and C3 encounters the flux tube of a stable auroral arc in the pre-midnight sector. C1 observes the mid cavity, while C3 enters the flux tube of the auroral arc at an altitude which is below the acceleration region, before crossing into the top half of the acceleration region. This allows us to study the boundary between the ionosphere and the density cavity, as well as large portion of the upper density cavity. The position of the two satellites, in relation to the acceleration region, is described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellites.The electron density exhibits an anti-correlation with the pseudo altitude, indicating that the lowest electron densities are found near the top of the density cavity. Over the entire pseudo altitude range, the electron density distribution is similar to a planar sheath, formed out of a plasma sheet dominated electron distribution, in response to the parallel electric field of the acceleration region. This indicates that the parallel electric fields on the ionosphere-cavity boundary, as well as the mid cavity parallel electric fields, are part of one unified structure rather than two discrete entities.The results highlight the strong connection between the auroral density cavity and auroral acceleration as well as the necessity of studying them in a unified fashion.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2015
Keyword
Auroral density cavity
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-176281 (URN)10.1002/2015JA021593 (DOI)000368252100014 ()2-s2.0-84954399402 (Scopus ID)
Note

QC 20160216

Available from: 2015-11-02 Created: 2015-11-02 Last updated: 2017-12-01Bibliographically approved
Alm, L., Li, B., Marklund, G. & Karlsson, T. (2015). Statistical altitude distribution of the auroral density cavity. Journal of Geophysical Research - Space Physics, 120(2), 996-1006.
Open this publication in new window or tab >>Statistical altitude distribution of the auroral density cavity
2015 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, 996-1006 p.Article in journal (Refereed) Published
Abstract [en]

The statistical altitude distribution of auroral density cavities located between 3.0 and 6.5 R-E is investigated using in situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R-E. Above 6.125 R-E, none of the events exhibit precipitating inverted V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R-E the pseudo altitude increases by 0.20 per R-E, consistent with a distributed parallel electric field. Between 4.375 and 5.625 R-E the pseudo altitude increases weakly, by 0.01 per R-E, due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R-E the pseudo altitude increases by 0.28 per R-E, due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-155704 (URN)10.1002/2014JA020691 (DOI)000351360800011 ()2-s2.0-84924811630 (Scopus ID)
Note

Updated from "Manuscript" to "Article". QC 20150420

Available from: 2014-11-10 Created: 2014-11-10 Last updated: 2017-12-05Bibliographically approved
Alm, L., Marklund, G. T. & Karlsson, T. (2014). In situ observations of density cavities extending above the auroral acceleration region. Journal of Geophysical Research - Space Physics, 119(7), 5286-5294.
Open this publication in new window or tab >>In situ observations of density cavities extending above the auroral acceleration region
2014 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 7, 5286-5294 p.Article in journal (Refereed) Published
Abstract [en]

The uppermost part of a stable potential structure in the auroral acceleration region was studied using simultaneous observations of Cluster satellites C1 and C3. Both satellites observe a monotonically decreasing electron density as they ascend through the auroral acceleration region. As C1 exits the top of the auroral acceleration region, the electron densities continue to decrease, and the minimum electron density is reached 14 km above the upper edge of the auroral acceleration region. The electron density does not return to noncavity values until the spacecraft exits the potential structure's flux tube. The data indicate that the auroral density cavity is not confined by the potential structure and may extend above the auroral acceleration region.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2014
Keyword
auroral acceleration region, auroral density cavity, potential structure
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-150940 (URN)10.1002/2014JA019799 (DOI)000340549000014 ()2-s2.0-84906309021 (Scopus ID)
Note

QC 20140912

QC 20151209

Available from: 2014-09-12 Created: 2014-09-11 Last updated: 2017-12-05Bibliographically approved
Li, B., Marklund, G., Alm, L., Karlsson, T., Lindqvist, P.-A. & Masson, A. (2014). Statistical altitude distribution of Cluster auroral electric fields, indicating mainly quasi-static acceleration below 2.8 R-E and Alfvenic above. Journal of Geophysical Research - Space Physics, 119(11), 8984-8991.
Open this publication in new window or tab >>Statistical altitude distribution of Cluster auroral electric fields, indicating mainly quasi-static acceleration below 2.8 R-E and Alfvenic above
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2014 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 11, 8984-8991 p.Article in journal (Refereed) Published
Abstract [en]

Results are presented from a statistical study of high-altitude electric fields and plasma densities using Cluster satellite data collected during 9.5years between 2 and 4 R-E. The average electric fields are most intense on the nightside and associated with an extensive plasma density cavity, with densities of 1cm(-3) or less. The intense electric fields are concentrated in two regions, separated by an altitude gap at about 2.8 R-E. Below this, the average electric field magnitudes reach about 50mV/m (mapped to the ionosphere) between 22 and 01 magnetic local time (MLT). Above 3 R-E, the fields are about twice as high and spread over a broader MLT range. These fields occur in a region where the (E/B)/V-A ratio is close to unity, which suggests an Alfvenic origin. The intense low-altitude electric fields are interpreted to be quasi-static, associated with the auroral acceleration region. This is supported by their location in MLT and altitude, and by a (E/B)/V-A ratio much below unity. The local electric field minimum between the two regions indicates a partial closure of the electrostatic potentials in the lower region. These results show similarities with model results of reflected Alfven waves by Lysak and Dum (1983), and with the O-shaped potential model, with associated wave-particle interaction at its top, proposed by Janhunen et al. (2000).

Keyword
quasi-static acceleration, Alfvénic acceleration, Statistical study, auroral electric fields
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-155703 (URN)10.1002/2014JA020225 (DOI)000346792100019 ()2-s2.0-84995695217 (Scopus ID)
Funder
Swedish National Space Board
Note

QC 20150130

Available from: 2014-11-10 Created: 2014-11-10 Last updated: 2017-12-05Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1594-1861

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