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Tian, A., Xiao, K., Degeling, A. W., Shi, Q., Park, J.-S., Nowada, M. & Pitkänen, T. (2020). Reconstruction of Plasma Structure with Anisotropic Pressure: Application to Pc5 Compressional Wave. Astrophysical Journal, 889(1), Article ID 35.
Open this publication in new window or tab >>Reconstruction of Plasma Structure with Anisotropic Pressure: Application to Pc5 Compressional Wave
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2020 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 889, no 1, article id 35Article in journal (Refereed) Published
Abstract [en]

The conventional Grad-Shafranov (GS) method is designed to reconstruct a two-dimensional magnetohydrostatic structure with isotropic pressure. In this work, we developed a new GS solver (GS-like) that includes the effect of pressure anisotropy based on reduced equations from Sonnerup et al. The new GS solver is benchmarked, and the results are compared with two other GS solvers based on the conventional GS method and that from Teh. This solver is applied to reconstruct a Pc5 compressional wave event, which has mirror-like features and includes a significant pressure anisotropy (p/p(parallel to) similar to 1.5, where p and p(parallel to) are the thermal pressures perpendicular and parallel to the magnetic field), observed by the Magnetospheric Multiscale mission in the duskside outer magnetosphere on 2015 September 19. The recovered maps indicate that, within some model constraints, the wave in the selected time interval consists of two magnetic bottle-like structures, each with an azimuthal size of about 9000 km (wavenumber similar to 44) and a larger field-aligned size. The spacecraft passed through the bottles at similar to 1600 km southward of the bottle centers. Further multispacecraft measurements revealed that the Pc5 compressional wave propagates sunward along with the background plasma and retains the bottle-like structures, driven mainly by the ion diamagnetic currents. The reconstructed magnetic topology is similar to that described in previous empirical or theoretical antisymmetric standing wave models. This Pc5 compressional wave is possibly driven by drift-mirror-like instabilities.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2020
Keywords
Planetary magnetosphere, Space plasmas
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-169478 (URN)10.3847/1538-4357/ab6296 (DOI)000520115500001 ()
Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
Hamrin, M., Gunell, H., Goncharov, O., De Spiegeleer, A., Fuselier, S., Mukherjee, J., . . . Giles, B. (2019). Can Reconnection be Triggered as a Solar Wind Directional Discontinuity Crosses the Bow Shock?: A Case of Asymmetric Reconnection. Journal of Geophysical Research - Space Physics, 124(11), 8507-8523
Open this publication in new window or tab >>Can Reconnection be Triggered as a Solar Wind Directional Discontinuity Crosses the Bow Shock?: A Case of Asymmetric Reconnection
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 11, p. 8507-8523Article in journal (Refereed) Published
Abstract [en]

Here we present some unique observations of reconnection at a quasi-perpendicular bow shock as an interplanetary directional discontinuity (DD) is crossing it simultaneously with the Magnetospheric Multiscale (MMS) mission. There are no burst data, but available data show indications of ongoing reconnection at the shock southward of MMS: a bifurcated current sheet with signatures of Hall magnetic and electric fields, normal magnetic fields indicating a magnetic connection between the two reconnecting regions, field-aligned currents and electric fields, E . J > 0 indicating a conversion of magnetic to kinetic energy, and subspin resolution ion energy-time spectrograms indicating ions being accelerated away from the X-line. The DD is also observed by four upstream spacecraft (ACE, WIND, Geotail, and ARTEMIS P1) and one downstream in the magnetosheath (Cluster 4), but none of them resolve signatures of ongoing reconnection. We therefore suggest that reconnection was temporarily triggered as the DD was compressed by the shock. Reconnection at the bow shock is inevitably asymmetric with both the density and magnetic field strength being higher on one side of the X-line (magnetosheath side) than on the other side where the plasma flow also is supersonic (solar wind side). This is different from the asymmetry exhibited at the more commonly studied case of asymmetric reconnection at the magnetopause. Asymmetric reconnection of the bow shock type has never been studied before, and the data discussed here present some first indications of the properties of the reconnection region for this type of reconnection.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-168193 (URN)10.1029/2019JA027006 (DOI)000505404700019 ()
Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-10Bibliographically approved
Pitkänen, T., Kullen, A., Laundal, K. M., Tenfjord, P., Shi, Q. Q., Park, J.-S., . . . Tian, A. M. (2019). IMF B-y Influence on Magnetospheric Convection in Earth's Magnetotail Plasma Sheet. Geophysical Research Letters, 46(21), 11698-11708
Open this publication in new window or tab >>IMF B-y Influence on Magnetospheric Convection in Earth's Magnetotail Plasma Sheet
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 21, p. 11698-11708Article in journal (Refereed) Published
Abstract [en]

We use Geotail, Cluster, and Time History of Events and Macroscale Interactions during Substorms data over 15 years (1995–2009) to statistically investigate convective ion flows (Vxy<200 km/s) in the magnetotail plasma sheet under the influence of a clearly nonzero dawn‐dusk interplanetary magnetic field (IMF By). We find that IMF By causes an interhemispheric asymmetry in the flows, which depends on the direction of IMF By. On the average, one magnetic hemisphere is dominated by a dawn‐dusk flow component, which is oppositely directed compared to that in the other hemisphere. This asymmetry is observed for both earthward and tailward flows. A comparison to tail By reveals that the region where the asymmetry in the average flows appears agrees with the appearance of the tail By direction collinear to IMF By. The results imply that IMF By has a major influence on the direction of the magnetic flux transport in the magnetotail.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-165336 (URN)10.1029/2019GL084190 (DOI)000494963200001 ()
Available from: 2019-11-26 Created: 2019-11-26 Last updated: 2020-05-04Bibliographically approved
De Spiegeleer, A., Hamrin, M., Gunell, H., Volwerk, M., Andersson, L., Karlsson, T., . . . Kistler, L. M. (2019). Oscillatory Flows in the Magnetotail Plasma Sheet: Cluster Observations of the Distribution Function. Journal of Geophysical Research - Space Physics, 124(4), 2736-2754
Open this publication in new window or tab >>Oscillatory Flows in the Magnetotail Plasma Sheet: Cluster Observations of the Distribution Function
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 4, p. 2736-2754Article in journal (Refereed) Published
Abstract [en]

Plasma dynamics in Earth's magnetotail is often studied using moments of the distribution function, which results in losing information on the kinetic properties of the plasma. To better understand oscillatory flows observed in the midtail plasma sheet, we investigate two events, one in each hemisphere, in the transition region between the central plasma sheet and the lobes using the 2-D ion distribution function from the Cluster 4 spacecraft. In this case study, the oscillatory flows are a manifestation of repeated ion flux enhancements with pitch angle changing from 0 degrees to 180 degrees in the Northern Hemisphere and from 180 degrees to 0 degrees in the Southern Hemisphere. Similar pitch angle signatures are observed seven times in about 80 min for the Southern Hemisphere event and three times in about 80 min for the Northern Hemisphere event. The ion flux enhancements observed for both events are slightly shifted in time between different energy channels, indicating a possible time-of-flight effect from which we estimate that the source of particle is located similar to 5-25R(E) and similar to 40-107R(E) tailward of the spacecraft for the Southern and Northern Hemisphere event, respectively. Using a test particle simulation, we obtain similar to 21-46 R-E for the Southern Hemisphere event and tailward of X similar to - 65R(E) (outside the validity region of the model) for the Northern Hemisphere event. We discuss possible sources that could cause the enhancements of ion flux.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-162349 (URN)10.1029/2018JA026116 (DOI)000477707800027 ()
Available from: 2019-08-27 Created: 2019-08-27 Last updated: 2020-05-04Bibliographically approved
De Spiegeleer, A., Hamrin, M., Volwerk, M., Karlsson, T., Gunell, H., Chong, G. S., . . . Nilsson, H. (2019). Oxygen Ion Flow Reversals in Earth's Magnetotail: A Cluster Statistical Study. Journal of Geophysical Research - Space Physics, 124(11), 8928-8942
Open this publication in new window or tab >>Oxygen Ion Flow Reversals in Earth's Magnetotail: A Cluster Statistical Study
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 11, p. 8928-8942Article in journal (Refereed) Published
Abstract [en]

We present a statistical study of magnetotail flows that change direction from earthward to tailward using Cluster spacecraft. More precisely, we study 318 events of particle flux enhancements in the O+ data for which the pitch angle continuously changes with time, either from 0 degrees to 180 degrees or from 180 degrees to 0 degrees. These structures are called "Pitch Angle Slope Structures" (PASSes). PASSes for which the pitch angle changes from 0 degrees to 180 degrees are observed in the Northern Hemisphere while those for which the pitch angle changes from 180 degrees to 0 degrees are observed in the Southern Hemisphere. These flux enhancements result in a reversal of the flow direction from earthward to tailward regardless of the hemisphere where they are observed. Sometimes, several PASSes can be observed consecutively which can therefore result in oscillatory velocity signatures in the earth-tail direction. The PASS occurrence rate increases from 1.8% to 3.7% as the AE index increases from similar to 0 to similar to 600 nT. Also, simultaneously to PASSes, there is typically a decrease in the magnetic field magnitude due to a decrease (increase) of the sunward component of the magnetic field in the Northern (Southern) Hemisphere. Finally, based on the 115 (out of 318) PASSes that show energy-dispersed structures, the distance to the source from the spacecraft is estimated to be typically R-E along the magnetic field line. This study is important as it sheds light on one of the causes of tailward velocities in Earth's magnetotail.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2019
Keywords
Earth's magnetotail, oxygen ions, velocity reversal, pitch angle distribution, Cluster, field aligned
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-166575 (URN)10.1029/2019JA027054 (DOI)000497604100001 ()
Available from: 2019-12-19 Created: 2019-12-19 Last updated: 2020-05-04Bibliographically approved
Pitkänen, T., Kullen, A., Shi, Q. Q., Hamrin, M., De Spiegeleer, A. & Nishimura, Y. (2018). Convection electric field and plasma convection in a twisted magnetotail: t THEMIS case study 1-2 January 2009. Journal of Geophysical Research - Space Physics, 123(9), 7486-7497
Open this publication in new window or tab >>Convection electric field and plasma convection in a twisted magnetotail: t THEMIS case study 1-2 January 2009
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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. 7486-7497Article in journal (Refereed) Published
Abstract [en]

We investigate THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1-2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB(y)-driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tail B-y < 0), the electric field is found to have northward E-z and tailward E-x components. During a positive twist (induced tail B-y > 0), the directions of E-z and E-x are reversed. The E-y component shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-153821 (URN)10.1029/2018JA025688 (DOI)000448376600025 ()
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Lindkvist, J., Hamrin, M., Gunell, H., Nilsson, H., Simon Wedlund, C., Kallio, E., . . . Karlsson, T. (2018). Energy conversion in cometary atmospheres: Hybrid modeling of 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 616, Article ID A81.
Open this publication in new window or tab >>Energy conversion in cometary atmospheres: Hybrid modeling of 67P/Churyumov-Gerasimenko
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A81Article in journal (Refereed) Published
Abstract [en]

Aims. We wish to investigate the energy conversion between particles and electromagnetic fields and determine the location where it occurs in the plasma environment of comets.

Methods. We used a hybrid plasma model that included photoionization, and we considered two cases of the solar extreme ultraviolet flux. Other parameters corresponded to the conditions of comet 67P/Churyumov-Gerasimenko at a heliocentric distance of 1.5 AU.

Results. We find that a shock-like structure is formed upstream of the comet and acts as an electromagnetic generator, similar to the bow shock at Earth that slows down the solar wind. The Poynting flux transports electromagnetic energy toward the inner coma, where newly born cometary ions are accelerated. Upstream of the shock-like structure, we find local energy transfer from solar wind ions to cometary ions. We show that mass loading can be a local process with a direct transfer of energy, but also part of a dynamo system with electromagnetic generators and loads.

Conclusions. The energization of cometary ions is governed by a dynamo system for weak ionization, but changes into a large conversion region with local transfer of energy directly from solar wind protons for high ionization.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
comets: individual: 67P/Churyumov-Gerasimenko, Sun: UV radiation, solar wind, methods: numerical, plasmas, acceleration of particles
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-148207 (URN)10.1051/0004-6361/201732353 (DOI)000442541100001 ()
Funder
Swedish National Space Board, 201/15Swedish National Space Board, 112/13Swedish Research Council, 2015-04187
Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2018-09-10Bibliographically approved
Vaverka, J., Pellinen-Wannberg, A., Kero, J., Mann, I., De Spiegeleer, A., Hamrin, M., . . . Pitkänen, T. (2017). Detection of EMPs generated by meteoroid impacts on the MMS spacecraft and problems with signal interpretation. In: 2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS): . Paper presented at 32nd General Assembly and Scientific Symposium of the International-Union-of-Radio-Science (URSI GASS), Montreal, QC, Canada, 19-26 August, 2017. IEEE
Open this publication in new window or tab >>Detection of EMPs generated by meteoroid impacts on the MMS spacecraft and problems with signal interpretation
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2017 (English)In: 2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), IEEE, 2017Conference paper, Published paper (Refereed)
Abstract [en]

Signatures of hypervelocity dust impacts detected by electric field instruments are still not completely understood. We have used the electric field instrument onboard one of the MMS spacecraft orbiting the Earth since 2015 to study various pulses in the measured electric field detected simultaneously by multiple antennas. This unique instrument allows a detailed investigation of registered waveforms. The preliminary results shown that the solitary waves can generate similar pulses as dust impacts and detected pulses can easily by misinterpreted when only one antenna is used.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-163055 (URN)10.23919/URSIGASS.2017.8105218 (DOI)000463723600268 ()978-90-825987-0-4 (ISBN)
Conference
32nd General Assembly and Scientific Symposium of the International-Union-of-Radio-Science (URSI GASS), Montreal, QC, Canada, 19-26 August, 2017
Available from: 2019-09-09 Created: 2019-09-09 Last updated: 2019-09-09Bibliographically approved
Vaverka, J., Pellinen-Wannberg, A., Kero, J., Mann, I., De Spiegeleer, A., Hamrin, M., . . . Pitkänen, T. (2017). Detection of meteoroid hypervelocity impacts on the Cluster spacecraft: First results. Journal of Geophysical Research - Space Physics, 122(6), 6485-6494
Open this publication in new window or tab >>Detection of meteoroid hypervelocity impacts on the Cluster spacecraft: First results
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 6, p. 6485-6494Article in journal (Refereed) Published
Abstract [en]

We present the first study of dust impact events on one of the Earth-orbiting Cluster satellites. The events were identified in the measurements of the wide band data (WBD) instrument on board the satellite operating in monopole configuration. Since 2009 the instrument is operating in this configuration due to the loss of three electric probes and is therefore measuring the potential between the only operating antenna and the spacecraft body. Our study shows that the WBD instrument on Cluster 1 is able to detect pulses generated by dust impacts and discusses four such events. The presence of instrumental effects, intensive natural waves, noncontinuous sampling modes, and the automatic gain control complicates this detection. Due to all these features, we conclude that the Cluster spacecraft are not ideal for dust impact studies. We show that the duration and amplitudes of the pulses recorded by Cluster are similar to pulses detected by STEREO, and the shape of the pulses can be described with the model of the recollection of impact cloud electrons by the positively charged spacecraft. We estimate that the detected impacts were generated by micron-sized grains with velocities in the order of tens of km/s.

Keywords
hypervelocity impact, dust detection, interplanetary dust
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-138045 (URN)10.1002/2016JA023755 (DOI)000405534800040 ()
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2019-09-09Bibliographically approved
De Spiegeleer, A., Hamrin, M., Pitkänen, T., Volwerk, M., Mann, I., Nilsson, H., . . . Vaverka, J. (2017). Low-frequency oscillatory flow signatures and high-speed flows in the Earth's magnetotail. Journal of Geophysical Research - Space Physics, 122(7), 7042-7056
Open this publication in new window or tab >>Low-frequency oscillatory flow signatures and high-speed flows in the Earth's magnetotail
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 7, p. 7042-7056Article in journal (Refereed) Published
Abstract [en]

Using plasma sheet data from Cluster 1 spacecraft from 2001 till 2011, we statistically investigate oscillatory signatures in the plasma bulk flow. These periodic oscillations are compared to high-speed and quiet flows. Periodic oscillations are observed approximately 8% of the time, while high-speed flows and quiet flows are observed around 0.5% and 12% of the time, respectively. We remark that periodic oscillations can roughly occur everywhere for x(gsm) < -10 R-E and |y(gsm)| < 10 RE, while quiet flows mainly occur toward the flanks of this region and toward x = -10 R-E. The relation between the geomagnetic and solar activity and the occurrence of periodic oscillations is investigated and reveal that periodic oscillations occur for most Kp values and solar activity, while quiet flows are more common during low magnetospheric and solar activity. We find that the median oscillation frequency of periodic oscillations is 1.7 mHz and the median duration of the oscillation events is 41 min. We also observe that their associated Poynting vectors show a tendency to be earthward (S-x >= 0). Finally, the distribution of high-speed flows and periodic oscillations as a function of the velocity is investigated and reveals that thresholds lower than 200 km/s should not be used to identify high-speed flows as it could result in misinterpreting a periodic oscillations for a high-speed flow.

Place, publisher, year, edition, pages
Washington: American Geophysical Union (AGU), 2017
Keywords
bursty bulk flows, plasma sheet, cluster observations, magnetic field, neutral sheet, magnetosphere, dependence, midtail
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:umu:diva-139015 (URN)10.1002/2017JA024076 (DOI)000407627100008 ()
Funder
Swedish National Space Board, 271/14
Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2020-05-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5681-0366

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