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Fuselier, S. A., Trattner, K. J., Petrinec, S. M., Denton, M. H., Toledo-Redondo, S., André, M., . . . Strangeway, R. J. (2019). Mass Loading the Earth's Dayside Magnetopause Boundary Layer and Its Effect on Magnetic Reconnection. Geophysical Research Letters, 46(12), 6204-6213
Open this publication in new window or tab >>Mass Loading the Earth's Dayside Magnetopause Boundary Layer and Its Effect on Magnetic Reconnection
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6204-6213Article in journal (Refereed) Published
Abstract [en]

When the interplanetary magnetic field is northward for a period of time, O+ from the high-latitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dual-lobe reconnection closes these field lines, which traps O+ and mass loads the boundary layer. This O+ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O+-rich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the high-shear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The high-latitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
magnetic reconnection, magnetosphere-ionosphere coupling, magnetopause, boundary layers
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-392876 (URN)10.1029/2019GL082384 (DOI)000477616300006 ()
Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-12-12Bibliographically approved
Bader, A., Wieser, G. S., André, M., Wieser, M., Futaana, Y., Persson, M., . . . Zhang, T. L. (2019). Proton Temperature Anisotropies in the Plasma Environment of Venus. Journal of Geophysical Research - Space Physics, 124(5), 3312-3330
Open this publication in new window or tab >>Proton Temperature Anisotropies in the Plasma Environment of Venus
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 5, p. 3312-3330Article in journal (Refereed) Published
Abstract [en]

Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T-perpendicular to) and parallel (T-parallel to) to the background magnetic field. We calculate average values of T-perpendicular to and T-parallel to for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T-perpendicular to/T-parallel to > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near-subsolar magnetosheath (T-perpendicular to/ T-parallel to approximate to 3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-389832 (URN)10.1029/2019JA026619 (DOI)000471601500011 ()
Funder
Swedish National Space Board, 96/15
Available from: 2019-07-29 Created: 2019-07-29 Last updated: 2019-07-29Bibliographically approved
Dimmock, A. P., Rosenqvist, L., Hall, J.-O., Viljanen, A., Yordanova, E., Honkonen, I., . . . Sjoberg, E. C. (2019). The GIC and Geomagnetic Response Over Fennoscandia to the 7-8 September 2017 Geomagnetic Storm. Space Weather: The international journal of research and applications, 17(7), 989-1010
Open this publication in new window or tab >>The GIC and Geomagnetic Response Over Fennoscandia to the 7-8 September 2017 Geomagnetic Storm
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2019 (English)In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 17, no 7, p. 989-1010Article in journal (Refereed) Published
Abstract [en]

Between 7 and 8 September 2017, Earth experienced extreme space weather events. We have combined measurements made by the IMAGE magnetometer array, ionospheric equivalent currents, geomagnetically induced current (GIC) recordings in the Finnish natural gas pipeline, and multiple ground conductivity models to study the Fennoscandia ground effects. This unique analysis has revealed multiple interesting physical and technical insights. We show that although the 7-8 September event was significant by global indices (Dst similar to 150 nT), it produced an unexpectedly large peak GIC. It is intriguing that our peak GIC did not occur during the intervals of largest geomagnetic depressions, nor was there any clear upstream trigger. Another important insight into this event is that unusually large and rare GIC amplitudes (>10 A) occurred in multiple Magnetic Local Time (MLT) sectors and could be associated with westward and eastward electrojets. We were also successfully able to model the geoelectric field and GIC using multiple models, thus providing a further important validation of these models for an extreme event. A key result from our multiple conductivity model comparison was the good agreement between the temporal features of 1-D and 3-D model results. This provides an important justification for past and future uses of 1-D models at Mantsala which is highly relevant to additional uses of this data set. Although the temporal agreement (after scaling) was good, we found a large (factor of 4) difference in the amplitudes between local and global ground models due to the difference in model conductivities. Thus, going forward, obtaining accurate ground conductivity values are key for GIC modeling.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-393132 (URN)10.1029/2018SW002132 (DOI)000479282100004 ()
Funder
Swedish Civil Contingencies Agency, 2016-2102
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-11-22Bibliographically approved
Eriksson, E., Vaivads, A., Graham, D. B., Divin, A., Khotyaintsev, Y. V., Yordanova, E. & André, M. (2018). Electron Energization at a Reconnecting Magnetosheath Current Sheet [Letter to the editor]. Geophysical Research Letters, 45(16)
Open this publication in new window or tab >>Electron Energization at a Reconnecting Magnetosheath Current Sheet
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16Article in journal, Letter (Refereed) Published
Abstract [en]

We present observations of electron energization within a sub-ion-scale magnetosheath current sheet (CS). A number of signatures indicate ongoing reconnection, including the thickness of the CS (∼0.7 ion inertial length), nonzero normal magnetic field, Hall magnetic fields with electrons carrying the Hall currents, and electron heating. We observe localized electron acceleration and heating parallel to the magnetic field at the edges of the CS. Electrostatic waves observed in these regions have low phase velocity and small wave potentials and thus cannot provide the observed acceleration and heating. Instead, we find that the electrons are accelerated by a parallel potential within the separatrix regions. Similar acceleration has been reported based on magnetopause and magnetotail observations.Thus, despite the different plasma conditions in magnetosheath, magnetopause, and magnetotail,the acceleration mechanism and corresponding heating of electrons is similar.

Keywords
magnetic reconnection, magnetosheath, electron heating, electron acceleration, Magnetospheric Multiscale
National Category
Other Physics Topics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-359592 (URN)10.1029/2018GL078660 (DOI)000445612500023 ()
Funder
Swedish Research Council, 2013-4309Swedish National Infrastructure for Computing (SNIC), m.2017-1-422Swedish National Infrastructure for Computing (SNIC), m.2016-457
Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2018-10-25Bibliographically approved
Norgren, C., Graham, D. B., Khotyaintsev, Y. V., André, M., Vaivads, A., Hesse, M., . . . Russell, C. T. (2018). Electron Reconnection in the Magnetopause Current Layer. Journal of Geophysical Research - Space Physics, 123(11), 9222-9238
Open this publication in new window or tab >>Electron Reconnection in the Magnetopause Current Layer
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 11, p. 9222-9238Article in journal (Refereed) Published
Abstract [en]

The electron dynamics within thin current sheets plays a key role both for the process of magnetic reconnection and other energy transfer mechanisms but, from an observational point of view, is not well understood. In this paper we report observations of a reconnecting current sheet with intermediate guide field B-G = 0.5B(in), where B-in is the magnetic field amplitude in the inflow regions. The current sheet width is comparable to electron spatial scales. It shows a bifurcated structure and is embedded within the magnetopause current layer with thickness of several ion scales. The electron scale current sheet has strong out-of-plane and in-plane currents, Hall electric and magnetic fields, a finite magnetic field component normal to the current sheet, and nongyrotropic electron distributions formed due to finite gyroradius effects at the boundary of the current sheet. Comparison between test particle simulations and electron data shows that electrons approaching from the edge of the largest magnetic curvature are scattered to perpendicular pitch angles in the center of the current sheet while electrons entering from the opposite side remain close to field aligned. The comparison also shows that an observed depletion in phase space at antiparallel pitch angles can be explained if an out-of-plane electric field, which due to the guide field is close to antiparallel to the magnetic field, is present in the center of the current sheet. This electric field would be consistent with the reconnection electric field, and we therefore interpret the depletion of electron phase space density as a manifestation of ongoing reconnection.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Geophysics Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-372832 (URN)10.1029/2018JA025676 (DOI)000453227400022 ()
Available from: 2019-01-09 Created: 2019-01-09 Last updated: 2019-01-09Bibliographically approved
Graham, D. B., Vaivads, A., Khotyaintsev, Y. V., Eriksson, A., André, M., Malaspina, D. M., . . . Plaschke, F. (2018). Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves. Journal of Geophysical Research - Space Physics, 123(9), 7534-7553
Open this publication in new window or tab >>Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7534-7553Article in journal (Refereed) Published
Abstract [en]

The spacecraft potential is often used to infer rapid changes in the thermal plasma density. The variations in spacecraft potential associated with large-amplitude Langmuir and upper hybrid waves are investigated with the Magnetospheric Multiscale (MMS) mission. When large-amplitude Langmuir and upper hybrid waves are observed, the spacecraft potential increases. The changes in spacecraft potential are shown to be due to enhanced photoelectron escape from the spacecraft when the wave electric fields reach large amplitude. The fluctuations in spacecraft potential follow the envelope function of the Langmuir and upper hybrid waves. Comparison with the high-resolution electron moments shows that the changes in spacecraft potential associated with the waves are not due to density perturbations. Indeed, using the spacecraft potential as a density probe leads to unphysically large density fluctuations. In addition, the changes in spacecraft potential are shown to increase as density decreases: larger spacecraft potential changes are observed in the magnetosphere, than in the magnetosheath and solar wind. These results show that external electric fields can lead to unphysical results when the spacecraft potential is used as a density probe. The results suggest that fluctuations in the spacecraft potential alone cannot be used to determine whether nonlinear processes associated with Langmuir and upper hybrid waves, such as the ponderomotive force and three-wave decay, are occurring.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
Keywords
Langmuir waves, photoelectron current, spacecraft potential, upper hybrid waves
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-369520 (URN)10.1029/2018JA025874 (DOI)000448376600029 ()
Funder
Swedish National Space Board, 175/15Swedish National Space Board, 128/17
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Li, K., Wei, Y., Haaland, S., Kronberg, E. A., Rong, Z. J., Maes, L., . . . Grigorenko, E. (2018). Estimating the Kinetic Energy Budget of the Polar Wind Outflow. Journal of Geophysical Research - Space Physics, 123(9), 7917-7929
Open this publication in new window or tab >>Estimating the Kinetic Energy Budget of the Polar Wind Outflow
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7917-7929Article in journal (Refereed) Published
Abstract [en]

Ionospheric outflow from the polar cap through the polar wind plays an important role in the evolution of the atmosphere and magnetospheric dynamics. Both solar illumination and solar wind energy input are known to be energy sources of the polar wind. However, observational studies of the energy transfer from these two energy sources to the polar wind are difficult. Because of their low energy, polar wind ions are invisible to regular ion detectors onboard a positively charged spacecraft. Using a new technique that indirectly measures these low-energy ions, we are able to estimate the energy budget of the polar wind. Our results show that solar illumination provides about 10(7) W of the kinetic energy of the polar wind, in addition to the energy transferred from the solar wind with a maximum rate of about 10(8) W. The energy transfer efficiency of solar illumination to the kinetic energy of the polar wind is about 6 to 7 orders of magnitude lower than that of the solar wind. Moreover, daily and seasonal changes in the orientation of the geomagnetic dipole axis control solar illumination over the polar cap, modulating both energies of the polar wind and energy transfer efficiencies from the two energy sources.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
Keywords
polar wind, ionospheric outflow, solar wind, solar illumination, energy transfer
National Category
Meteorology and Atmospheric Sciences Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-369521 (URN)10.1029/2018JA025819 (DOI)000448376600054 ()
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Odelstad, E., Eriksson, A. I., Johansson, F. L., Vigren, E., Henri, P., Gilet, N., . . . André, M. (2018). Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P. Journal of Geophysical Research - Space Physics, 123(7), 5870-5893
Open this publication in new window or tab >>Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 7, p. 5870-5893Article in journal (Refereed) Published
Abstract [en]

Abstract A major point of interest in cometary plasma physics has been the diamagnetic cavity, an unmagnetized region in the innermost part of the coma. Here we combine Langmuir and Mutual Impedance Probe measurements to investigate ion velocities and electron temperatures in the diamagnetic cavity of comet 67P, probed by the Rosetta spacecraft. We find ion velocities generally in the range 2?4 km/s, significantly above the expected neutral velocity 1 km/s, showing that the ions are (partially) decoupled from the neutrals, indicating that ion-neutral drag was not responsible for balancing the outside magnetic pressure. Observations of clear wake effects on one of the Langmuir probes showed that the ion flow was close to radial and supersonic, at least with respect to the perpendicular temperature, inside the cavity and possibly in the surrounding region as well. We observed spacecraft potentials  V throughout the cavity, showing that a population of warm (?5 eV) electrons was present throughout the parts of the cavity reached by Rosetta. Also, a population of cold ( ) electrons was consistently observed throughout the cavity, but less consistently in the surrounding region, suggesting that while Rosetta never entered a region of collisionally coupled electrons, such a region was possibly not far away during the cavity crossings.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
comets, Rosetta, plasma, diamagnetic cavity, ion velocity, electron temperature
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-356424 (URN)10.1029/2018JA025542 (DOI)000442664300043 ()
Funder
Swedish National Space Board, 109/12, 168/15, 166/14Swedish Research Council, 621-2013-4191
Note

Article published in Early View on 25 July, 2018

Available from: 2018-07-26 Created: 2018-07-26 Last updated: 2018-11-05Bibliographically approved
Graham, D. B., Vaivads, A., Khotyaintsev, Y. V., André, M., Le Contel, O., Malaspina, D. M., . . . Torbert, R. B. (2018). Large-Amplitude High-Frequency Waves at Earth's Magnetopause. Journal of Geophysical Research - Space Physics, 123(4), 2630-2657
Open this publication in new window or tab >>Large-Amplitude High-Frequency Waves at Earth's Magnetopause
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2630-2657Article in journal (Refereed) Published
Abstract [en]

Large-amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1Vm(-1), and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
Keywords
plasma waves, magnetopause
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357762 (URN)10.1002/2017JA025034 (DOI)000433498400012 ()
Funder
Swedish National Space Board, 175/15
Available from: 2018-08-23 Created: 2018-08-23 Last updated: 2018-08-23Bibliographically approved
Alm, L., André, M., Vaivads, A., Khotyaintsev, Y. V., Torbert, R. B., Burch, J. L., . . . Mauk, B. H. (2018). Magnetotail Hall Physics in the Presence of Cold Ions. Geophysical Research Letters, 45(20), 10941-10950
Open this publication in new window or tab >>Magnetotail Hall Physics in the Presence of Cold Ions
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 20, p. 10941-10950Article in journal (Refereed) Published
Abstract [en]

We present the first in situ observation of cold ionospheric ions modifying the Hall physics of magnetotail reconnection. While in the tail lobe, Magnetospheric Multiscale mission observed cold (tens of eV) E x B drifting ions. As Magnetospheric Multiscale mission crossed the separatrix of a reconnection exhaust, both cold lobe ions and hot (keV) ions were observed. During the closest approach of the neutral sheet, the cold ions accounted for similar to 30% of the total ion density. Approximately 65% of the initial cold ions remained cold enough to stay magnetized. The Hall electric field was mainly supported by the j x B term of the generalized Ohm's law, with significant contributions from the del center dot P-e and v(c) x B terms. The results show that cold ions can play an important role in modifying the Hall physics of magnetic reconnection even well inside the plasma sheet. This indicates that modeling magnetic reconnection may benefit from including multiscale Hall physics. Plain Language Summary Cold ions have the potential of changing the fundamental physics behind magnetic reconnection. Here we present the first direct observation of this process in action in the magnetotail. Cold ions from the tail lobes were able to remain cold even deep inside the much hotter plasma sheet. Even though the cold ions only accounted for similar to 30% of the total ions, they had a significant impact on the electric fields near the reconnection region.

National Category
Geophysics Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-372422 (URN)10.1029/2018GL079857 (DOI)000451510500017 ()
Funder
Swedish National Space Board, SNSB 176/15Swedish National Space Board, 158/16
Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-12-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-3725-4920

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