Endre søk
Begrens søket
12345 151 - 200 of 220
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 151.
    Oieroset, M.
    et al.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA. rake, J. F..
    Phan, T. D.
    Drake, J. F.
    Eastwood, J. P.
    Fuselier, S. A.
    Strangeway, R. J.
    Haggerty, C.
    Shay, M. A.
    Oka, M.
    Wang, S.
    Chen, L-J
    Kacem, I
    Lavraud, B.
    Angelopoulos, V
    Burch, J. L.
    Torbert, R. B.
    Ergun, R. E.
    Khotyaintsev, Y.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Gershman, D. J.
    Giles, B. L.
    Pollock, C.
    Moore, T. E.
    Russell, C. T.
    Saito, Y.
    Avanov, L. A.
    Paterson, W.
    Reconnection With Magnetic Flux Pileup at the Interface of Converging ts at the Magnetopause2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 4, s. 1937-1946Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report Magnetospheric Multiscale observations of reconnection in a in current sheet at the interface of interlinked flux tubes carried by nverging reconnection jets at Earth's magnetopause. The ion skin pth-scale width of the interface current sheet and the non-frozen-in ns indicate that Magnetospheric Multiscale crossed the reconnection yer near the X-line, through the ion diffusion region. Significant leup of the reconnecting component of the magnetic field in this and ree other events on approach to the interface current sheet was companied by an increase in magnetic shear and decrease in , leading conditions favorable for reconnection at the interface current sheet. e pileup also led to enhanced available magnetic energy per particle d strong electron heating. The observations shed light on the olution and energy release in 3-D systems with multiple reconnection tes. ain Language Summary The Earth and the solar wind magnetic fields terconnect through a process called magnetic reconnection. The newly connected magnetic field lines are strongly bent and accelerate rticles, similar to a rubber band in a slingshot. In this paper we ve used observations from NASA's Magnetospheric MultiScale spacecraft investigate what happens when two of these slingshot-like magnetic eld lines move toward each other and get tangled up. We found that the o bent magnetic field lines tend to orient themselves perpendicular to ch other as they become interlinked and stretched, similar to what bber bands would do. This reorientation allows the interlinked gnetic fields to reconnect again, releasing part of the built-up gnetic energy as strong electron heating. The results are important cause they show how interlinked magnetic fields, which occur in many lar and astrophysics contexts, reconnect and produce enhanced electron ating, something that was not understood before.

  • 152. Oieroset, M.
    et al.
    Phan, T. D.
    Haggerty, C.
    Shay, M. A.
    Eastwood, J. P.
    Gershman, D. J.
    Drake, J. F.
    Fujimoto, M.
    Ergun, R. E.
    Mozer, F. S.
    Oka, M.
    Torbert, R. B.
    Burch, J. L.
    Wang, S.
    Chen, L. J.
    Swisdak, M.
    Pollock, C.
    Dorelli, J. C.
    Fuselier, S. A.
    Lavraud, B.
    Giles, B. L.
    Moore, T. E.
    Saito, Y.
    Avanov, L. A.
    Paterson, W.
    Strangeway, R. J.
    Russell, C. T.
    Khotyaintsev, Y.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Malakit, K.
    MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 11, s. 5536-5544Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (d(i)) width) current sheet (at similar to 12 d(i) downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

  • 153.
    Oimatsu, S.
    et al.
    Kyoto Univ, Grad Sch Sci, Kyoto, Japan..
    Nose, M.
    Kyoto Univ, Grad Sch Sci, Kyoto, Japan..
    Teramoto, M.
    Nagoya Univ, Inst Space Earth Environm Res, Nagoya, Aichi, Japan..
    Yamamoto, K.
    Kyoto Univ, Grad Sch Sci, Kyoto, Japan..
    Matsuoka, A.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Tokyo, Japan..
    Kasahara, S.
    Univ Tokyo, Grad Sch Sci, Tokyo, Japan..
    Yokota, S.
    Osaka Univ, Grad Sch Sci, Suita, Osaka, Japan..
    Keika, K.
    Univ Tokyo, Grad Sch Sci, Tokyo, Japan..
    Le, G.
    NASA, Heliophys Sci Div, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Nomura, R.
    Japan Aerosp Explorat Agcy, Environm Test Technol Unit, Tokyo, Japan..
    Fujimoto, A.
    Kyushu Univ, Int Ctr Space Weather Sci & Educ, Fukuoka, Fukuoka, Japan..
    Sormakov, D.
    Arctic & Antarctic Res Inst, St Petersburg, Russia..
    Troshichev, O.
    Arctic & Antarctic Res Inst, St Petersburg, Russia..
    Tanaka, Y. -M
    Shinohara, M.
    Kagoshima Coll, Natl Inst Technol, Kagoshima, Japan..
    Shinohara, I.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Tokyo, Japan..
    Miyoshi, Y.
    Nagoya Univ, Inst Space Earth Environm Res, Nagoya, Aichi, Japan..
    Slavin, J. A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Denver, CO 80202 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Drift-Bounce Resonance Between Pc5 Pulsations and Ions at Multiple Energies in the Nightside Magnetosphere: Arase and MMS Observations2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 15, s. 7277-7286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Pc5 wave is observed by the Exploration of energization and Radiation in Geospace Arase satellite in the inner magnetosphere (L similar to 5.4-6.1) near postmidnight (L-magnetic local time similar to 1.8-2.5 hr) during the storm recovery phase on 27 March 2017. Its azimuthal wave number (m-number) is estimated using two independent methods with satellites and ground observations to be -8 to -15. The direct measurement of the m-number enables us to calculate the resonance energy. The flux oscillations of H+ and O+ ions at >= 56.3 keV are caused by drift resonance and those of O+ ions at <= 18.6 keV by bounce resonance. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. The enhancement of the O+/H+ flux ratio at <= 18.6 keV indicates selective acceleration of O+ ions through bounce resonance. Plain Language Summary Geomagnetic pulsations are magnetic fluctuations excited by solar wind or plasma instabilities in the magnetosphere. Pc5 waves are continuous geomagnetic pulsations with a period of 150-600 s. A Pc5 wave was observed in the inner magnetosphere during a magnetic storm on 27 March 2017. It propagated westward with a wave number of 8 to 15 and resonated with charged particles, resulting in oscillations of the H+ and O+ ion fluxes at >= 56.3 keV and the O+ ion fluxes at <= 18.6 keV. Resonances of O+ ions at multiple energies are simultaneously observed for the first time. At the same time, the O+/H+ flux ratio at <= 18.6 keV enhanced corresponding to the O+ ion flux oscillations, which indicates selective acceleration of O+ ions through resonances.

  • 154. Oka, M.
    et al.
    Wilson, L. B. , I I I
    Phan, T. D.
    Hull, A. J.
    Amano, T.
    Hoshino, M.
    Argall, M. R.
    Le Contel, O.
    Agapitov, O.
    Gershman, D. J.
    Khotyaintsev, Y. V.
    Burch, J. L.
    Torbert, R. B.
    Pollock, C.
    Dorelli, J. C.
    Giles, B. L.
    Moore, T. E.
    Saito, Y.
    Avanov, L. A.
    Paterson, W.
    Ergun, R. E.
    Strangeway, R. J.
    Russell, C. T.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Electron Scattering by High-frequency Whistler Waves at Earth's Bow Shock2017Inngår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, nr 2, artikkel-id L11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of nonthermal electrons by whistler waves at Earth's bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvn Mach number similar to 11 and a shock angle similar to 84 degrees. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5-2 keV) electron flux, correlated with high-frequency (0.2-0.4 Omega(ce), where Omega(ce) is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

  • 155. ORSINI, S
    et al.
    AMATA, E
    CANDIDI, M
    BALSIGER, H
    STOKHOLM, M
    HUANG, C
    LENNARTSSON, W
    Lindqvist, Per-Arne
    KTH. Plasma fysik.
    COLD STREAMS OF IONOSPHERIC OXYGEN IN THE PLASMA SHEET DURING THE CDAW-6 EVENT OF MARCH 22, 19791985Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 90, nr NA5, s. 4091-4098Artikkel i tidsskrift (Fagfellevurdert)
  • 156. Orsini, S.
    et al.
    Amata, E.
    Candidi, M.
    Pedersen, A.
    Stokholm, M.
    Lindqvist, Per-Arne
    KTH.
    DC ELECTRIC FIELD IN SPACE: DIRECT MEASUREMENTS AND INFERENCES FROM COLD PLASMA DRIFTS.1983Inngår i: Proceedings of the 17th ESLAB Symposium, 1983, s. 69-72Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Data from the satellites GEOS-2 and ISEE are used for a comparison between electric fields directly measured on board satellites and inferred from drift properties of ambient plasma. It is found that, within the errors, a satisfactory agreement exists.

  • 157.
    Pan, Dong-Xiao
    et al.
    Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China.;Swedish Inst Space Phys, Uppsala, Sweden..
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, Daniel B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, Andris
    Swedish Inst Space Phys, Uppsala, Sweden..
    Zhou, Xu-Zhi
    Peking Univ, Sch Earth & Space Sci, Beijing, Peoples R China..
    Andre, Mats
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ergun, Robert E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Le Contel, Olivier
    Univ Paris Sud, Sorbonne Univ, Lab Phys Plasmas, CNRS,Ecole Polytech,Obs Paris, Paris, France..
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Torbert, Roy B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Giles, Barbara
    NASA Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Rippled Electron-Scale Structure of a Dipolarization Front2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 22, s. 12116-12124Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use the Magnetospheric Multiscale mission to investigate electron-scale structures at a dipolarization front. The four spacecraft are separated by electron scales and observe large differences in plasma and field parameters within the dipolarization front, indicating strong deviation from typically assumed plane or slightly curved front surface. We attribute this to ripples generated by the lower hybrid drift instability (LHDI) with wave number of k(rho e)similar or equal to 0.4 and maximum wave potential of similar to 1 kV similar to k(B)T(e). Power law-like spectra of E-perpendicular to with slope of -3 indicates the turbulent cascade of LHDI. LHDI is observed together with bursty high-frequency parallel electric fields, suggesting coupling of LHDI to higher-frequency electrostatic waves. Plain Language Summary Dipolarization fronts (DFs) are narrow boundaries with sharp enhancement of magnetic field, located at the leading part of fast plasma jets observed in Earth's magnetotail. DFs are typically assumed to be smooth boundaries at scales comparable to the ion gyroradius and below. In this study, we use the four Magnetospheric Multiscale spacecraft separated by several electron gyroradii to investigate fine structure of a DF. Surprisingly, we observe significant differences in the fields and plasma measurements between the spacecraft despite their small separation. We attribute these signatures to electron-scale disturbances propagating along the DF surface, and thus the DF surface is not smooth as expected but rather rippled. The ripples develop as a result of a plasma instability driven by the strong inhomogeneities present at the DF. The fact that the ripples have such small scales means that they can effectively interact with plasma electrons.

  • 158. Pedersen, A.
    et al.
    Cattell, C.A.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner.
    Formisano, V.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner.
    Mozer, F.S.
    Torbert, R.B.
    Quasistatic electric field measurements with spherical double probes on the GEOS and ISEE satellites1984Inngår i: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 37, s. 269-312Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spherical double probes for measurements of electric fields on the GEOS-1, GEOS-2, and ISEE-1 satellites are described. An essential feature of these satellites is their conductive surfaces which eliminate errors due to differential charging and enable meaningful diagnostic experiments to be carried out. The result of these experiments is a good understanding of interactions between the plasma, the satellite and the probes, including photo-electron emission on satellite and probes. Electric field measurements are compared with measurements of plasma drift perpendicular to the magnetic field in the solar wind and the magnetosphere and the error bar for the absolute values of the electric field is found to be in the range ±(0.5-1.0) mV m-1 whereas relative variations can be determined with much better accuracy. A useful by-product from a spherical double probe system is the determination of satellite floating potential which is related to the plasma electron flux. This measurement allows high time resolution studies of boundary crossings. Examples of electric field measurements, which reflect the recent scientific results, are given for different regions of the magnetosphere from the bow shock, the inner magnetosphere and the tail. Several examples of simultaneous GEOS-ISEE observations are described. © 1984 D. Reidel Publishing Company.

  • 159. Pedersen, A.
    et al.
    Cattell, C.A.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Knott, K.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Manka, R.H.
    Mozer, F.S.
    Electric fields in the plasma sheet and plasma sheet boundary layer1985Inngår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol. 90, s. 1231-1242Artikkel i tidsskrift (Fagfellevurdert)
  • 160. Pedersen, A.
    et al.
    Decreau, P.
    Escoubet, C. P.
    Gustafsson, G.
    Laakso, H.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner (före 2005), Alfvénlaboratoriet.
    Lybekk, B.
    Masson, A.
    Mozer, F.
    Vaivads, Andris
    Four-point high time resolution information on electron densities by the electric field experiments (EFW) on cluster2001Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, nr 12-okt, s. 1483-1489Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For accurate measurements of electric fields, spherical double probes are electronically controlled to be at a positive potential of approximately 1 V relative to the ambient magnetospheric plasma. The spacecraft will acquire a potential which balances the photoelectrons escaping to the plasma and the electron flux collected from the plasma. The probe-to-plasma potential difference can be measured with a time resolution of a fraction of a second, and provides information on the electron density over a wide range of electron densities from the lobes (similar to0.01 cm(-3)) to the magnetosheath (> 10 cm(-3)) and the plasmasphere (> 100 cm(-3)). This technique has been perfected and calibrated against other density measurements on GEOS, ISEE-1, CRRES, GEOTAIL and POLAR. The Cluster spacecraft potential measurements opens the way for new approaches, particularly near boundaries and gradients where four-point measurements will provide information never obtained before. Another interesting point is that onboard data storage of this simple parameter can be done for complete orbits and thereby will provide background information for the shorter full data collection periods on Cluster. Preliminary calibrations against other density measurements on Cluster will be reported.

  • 161. Pedersen, A.
    et al.
    Lybekk, B.
    Andre, M.
    Eriksson, Anders
    Swedish Institute of Space Physics, Sweden.
    Masson, A.
    Mozer, F. S.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Decreau, P. M. E.
    Dandouras, I.
    Sauvaud, J. A.
    Fazakerley, A.
    Taylor, M.
    Paschmann, G.
    Svenes, K. R.
    Torkar, K.
    Whipple, E.
    Electron density estimations derived from spacecraft potential measurements on Cluster in tenuous plasma regions2008Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, nr A7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spacecraft potential measurements by the EFW electric field experiment on the Cluster satellites can be used to obtain plasma density estimates in regions barely accessible to other type of plasma experiments. Direct calibrations of the plasma density as a function of the measured potential difference between the spacecraft and the probes can be carried out in the solar wind, the magnetosheath, and the plasmashere by the use of CIS ion density and WHISPER electron density measurements. The spacecraft photoelectron characteristic ( photoelectrons escaping to the plasma in current balance with collected ambient electrons) can be calculated from knowledge of the electron current to the spacecraft based on plasma density and electron temperature data from the above mentioned experiments and can be extended to more positive spacecraft potentials by CIS ion and the PEACE electron experiments in the plasma sheet. This characteristic enables determination of the electron density as a function of spacecraft potential over the polar caps and in the lobes of the magnetosphere, regions where other experiments on Cluster have intrinsic limitations. Data from 2001 to 2006 reveal that the photoelectron characteristics of the Cluster spacecraft as well as the electric field probes vary with the solar cycle and solar activity. The consequences for plasma density measurements are addressed. Typical examples are presented to demonstrate the use of this technique in a polar cap/lobe plasma.

  • 162. Peng, F. Z.
    et al.
    Fu, H. S.
    Cao, J. B.
    Graham, D. B.
    Chen, Z. Z.
    Cao, D.
    Xu, Y.
    Huang, S. Y.
    Wang, T. Y.
    Khotyaintsev, Y. V.
    Andre, M.
    Russell, C. T.
    Giles, B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Torbert, R. B.
    Ergun, R. E.
    Burch, J. L.
    Quadrupolar pattern of the asymmetric guide-field reconnection2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 6, s. 6349-6356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With high-resolution data of the recently launched Magnetospheric Multiscale mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry N-high/N-low approximate to 2 on the two sides of the reconnecting current sheet and a guide field B-g approximate to 0.4B(0) in the out-of-plane direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the out-of-plane direction, and the corresponding Hall currents. Obviously, the density asymmetry N-high/N-low approximate to 2 and the guide field B-g approximate to 0.4B(0) are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.

  • 163. Phan, T. D.
    et al.
    Eastwood, J. P.
    Cassak, P. A.
    Oieroset, M.
    Gosling, J. T.
    Gershman, D. J.
    Mozer, F. S.
    Shay, M. A.
    Fujimoto, M.
    Daughton, W.
    Drake, J. F.
    Burch, J. L.
    Torbert, R. B.
    Ergun, R. E.
    Chen, L. J.
    Wang, S.
    Pollock, C.
    Dorelli, J. C.
    Lavraud, B.
    Giles, B. L.
    Moore, T. E.
    Saito, Y.
    Avanov, L. A.
    Paterson, W.
    Strangeway, R. J.
    Russell, C. T.
    Khotyaintsev, Y.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Oka, M.
    Wilder, F. D.
    MMS observations of electron-scale filamentary currents in the reconnection exhaust and near the X line2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 12, s. 6060-6069Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report Magnetospheric Multiscale observations of macroscopic and electron-scale current layers in asymmetric reconnection. By intercomparing plasma, magnetic, and electric field data at multiple crossings of a reconnecting magnetopause on 22 October 2015, when the average interspacecraft separation was similar to 10 km, we demonstrate that the ion and electron moments are sufficiently accurate to provide reliable current density measurements at 30ms cadence. These measurements, which resolve current layers narrower than the interspacecraft separation, reveal electron-scale filamentary Hall currents and electron vorticity within the reconnection exhaust far downstream of the X line and even in the magnetosheath. Slightly downstream of the X line, intense (up to 3 mu A/m(2)) electron currents, a super-Alfvenic outflowing electron jet, and nongyrotropic crescent shape electron distributions were observed deep inside the ion-scale magnetopause current sheet and embedded in the ion diffusion region. These characteristics are similar to those attributed to the electron dissipation/diffusion region around the X line.

  • 164.
    Phan, T. D.
    et al.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Eastwood, J. P.
    Imperial Coll London, Blackett Lab, London, England..
    Shay, M. A.
    Univ Delaware, Newark, DE USA..
    Drake, J. F.
    Univ Maryland, College Pk, MD 20742 USA..
    Sonnerup, B. U. O.
    Dartmouth Coll, Hanover, NH 03755 USA..
    Fujimoto, M.
    JAXA, ISAS, Sagamihara, Kanagawa, Japan..
    Cassak, P. A.
    West Virginia Univ, Morgantown, WV USA..
    Oieroset, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Durham, NH 03824 USA..
    Rager, A. C.
    Catholic Univ Amer, Washington, DC 20064 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C.
    Denali Sci, Healy, AK USA..
    Pyakurel, P. S.
    Univ Delaware, Newark, DE USA..
    Haggerty, C. C.
    Univ Delaware, Newark, DE USA..
    Khotyaintsev, Y.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, Toulouse, France..
    Saito, Y.
    JAXA, ISAS, Sagamihara, Kanagawa, Japan..
    Oka, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Retino, A.
    Ecole Polytech, CNRS, Paris, France..
    Le Contel, O.
    Ecole Polytech, CNRS, Paris, France..
    Argall, M. R.
    Univ New Hampshire, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Moore, T. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Wilder, F. D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Russell, C. T.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath2018Inngår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 557, nr 7704, s. 202-+Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic reconnection in current sheets is a magnetic-to-particle energy conversion process that is fundamental to many space and laboratory plasma systems. In the standard model of reconnection, this process occurs in a minuscule electron-scale diffusion region(1,2). On larger scales, ions couple to the newly reconnected magnetic-field lines and are ejected away from the diffusion region in the form of bi-directional ion jets at the ion Alfven speed(3-5). Much of the energy conversion occurs in spatially extended ion exhausts downstream of the diffusion region(6). In turbulent plasmas, which contain a large number of small-scale current sheets, reconnection has long been suggested to have a major role in the dissipation of turbulent energy at kinetic scales(7-11). However, evidence for reconnection plasma jetting in small-scale turbulent plasmas has so far been lacking. Here we report observations made in Earth's turbulent magnetosheath region (downstream of the bow shock) of an electron-scale current sheet in which diverging bi-directional super-ion-Alfvenic electron jets, parallel electric fields and enhanced magnetic-to-particle energy conversion were detected. Contrary to the standard model of reconnection, the thin reconnecting current sheet was not embedded in a wider ion-scale current layer and no ion jets were detected. Observations of this and other similar, but unidirectional, electron jet events without signatures of ion reconnection reveal a form of reconnection that can drive turbulent energy transfer and dissipation in electron-scale current sheets without ion coupling.

  • 165. Popielawska, B.
    et al.
    Stasiewicz, K.
    Lindqvist, Per-Arne
    KTH.
    Aparicio, B.
    An imprint of the quiet plasma sheet structure at the orbit of viking: Magnetosphere without substorms1996Inngår i: European Space Agency, (Special Publication) ESA SP, ISSN 0379-6566, nr 389, s. 133-139Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a study of the plasma sheet structure as seen on VIKING during prolonged periods of magnetic quiescence. The ion and electron spectrograms, the electric field data and field-aligned current signatures in the magnetic field data are examined. A special attention is paid to cases when the Low Latitude Boundary Layer-like plasma is seen deep in the nightside at latitudes which apparently map to close geocentric distances as it implies an exotic plasma circulation in the tail. An attempt has been made to infer from VIKING data how the quiet plasma sheet is formed, whether it originates mainly from the mantle source via the interaction with the distant tail current sheet or whether the lateral transport of the Low Latitude Boundary Layer (LLBL) from the tail flanks (with essentially adiabatic particle motion) takes place followed by the sunward convection in the central part of the near-Earth tail. The VIKING plasma and electric field data suggest that the last mechanism is decisive for plasma sheet structuring during prolonged periods of northward IMF.

  • 166. POTEMRA, TA
    et al.
    ZANETTI, LJ
    BYTHROW, PF
    ERLANDSON, RE
    LUNDIN, R
    Marklund, Göran T.
    KTH.
    BLOCK, LP
    Lindqvist, Per-Arne
    KTH.
    RESONANT GEOMAGNETIC-FIELD OSCILLATIONS AND BIRKELAND CURRENTS IN THE MORNING SECTOR1988Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 93, nr A4, s. 2661-2674Artikkel i tidsskrift (Fagfellevurdert)
  • 167. Puhl-Quinn, P. A.
    et al.
    Matsui, H.
    Jordanova, V. K.
    Khotyaintsev, Y.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    An effort to derive an empirically based, inner-magnetospheric electric field model: Merging Cluster EDI and EFW data2008Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 70, nr 2-4, s. 564-573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A key ingredient for modelling many inner-magnetospheric processes is the realistic representation of the spatio-temporal dynamics of the inner-magnetospheric electric field, or, IMEF The Cluster Mission provides a unique opportunity to construct an IMEF model using electric field measurements from both the electron drift instrument (EDI) and the electric fields and waves instrument (EFW). A superset of IMEF data is formed by merging EDI and EFW data. Challenges presented by the merging process include the handling of compromised perpendicular electric field (E-L) calculations, electric field offsets, scaling problems, and spurious fields. The present goal is to produce the highest quality merged IMEF data set possible which is minimally affected by these issues. Preliminary investigation of the merging process on Cluster I for the years 2001-2003 has revealed that merging is a worthwhile exercise. The data sets are shown to be complementary, and the IMEF merged data set is superior to either data set alone in terms of improved spatial coverage, and coverage of a wider range of geomagnetic activity levels. Preliminary use of the merged IMEF data set to construct a parameterized, equatorial, electric field model for the inner magnetosphere, the UNH-IMEF model, is also presented. The electric field morphology produced by this preliminary version of the UNH-IMEF model shows the expected sensitivity to IMF orientation.

  • 168.
    Ren, Y.
    et al.
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Dai, L.
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Li, W.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA..
    Tao, X.
    Univ Sci & Technol China, Dept Geophys & Planetary Sci, CAS Key Lab Geospace Environm, Hefei, Anhui, Peoples R China..
    Wang, C.
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Tang, B.
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, CNRS, UPS,CNES, Toulouse, France..
    Wu, Y.
    Univ Sci & Technol China, Dept Geophys & Planetary Sci, CAS Key Lab Geospace Environm, Hefei, Anhui, Peoples R China..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, Paris, France..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Earth & Planetary Sci, Los Angeles, CA USA..
    Ergun, R. E.
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China.;Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik. Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Whistler Waves Driven by Field-Aligned Streaming Electrons in the Near-Earth Magnetotail Reconnection2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 10, s. 5045-5054Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyze Magnetospheric Multiscale Mission observations of whistler waves and associated electron field-aligned crescent distribution in the vicinity of the magnetotail near-Earth X-line. The whistler waves propagate outward from the X-line in the neutral sheet. The associated field-aligned streaming electrons exhibit a crescent-like shape, with an inverse slope (df/d vertical bar v(parallel to)vertical bar > 0) at 1-5 keV. The parallel phase velocity of the waves is in the range (1-5 keV) of the inverse slope of the field-aligned crescents in the velocity space. We demonstrate that the observed whistler waves are driven by the electron field-aligned crescents through Landau resonance. The cyclotron resonance is at the high-energy tail with negligible free energy of pitch angle anisotropy in these events.

  • 169.
    Sadeghi, Soheil
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Nilsson, Hans
    Marghitu, Octab
    Zhang, Y.
    Fazakerley, Andrew
    Lucek, Elisabeth
    Cluster Observations of Quasi-Static Potential Structures Overlapping with Alfvénic Regions2012Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Results are presented from an equatorward crossing of the Cluster spacecraft through the high-altitude auroral acceleration region, over a system of East-West aligned auroral arcs in the Southern hemisphere auroral oval. The event occurred during quiet geomagnetic conditions during the expansion phase of a weak substorm. Acceleration potential profiles of the quasi-static structures are determined from the particle and field data. The observations reveal a dynamically developing system of small-scale and large-scale quasi-static structures overlapping with Alfvénic regions. Such overlaps are found within the PSBL and inside the Region 2 of downward currents. No density cavities are seen in the overlap regions. Growths of small-scale potential structures were observed in the PSBL and in the middle of Region 2, during the ~1.5 minutes between the Cluster 4 and Cluster 3 passages. During this period, the Alfvénic regions retreated both at the poleward and equatorward oval boundaries, and the large-scale quasi-static potentials intensified.

  • 170.
    Sadeghi, Soheil
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Marghitu, Octav
    Space Plasma and Magnetometry Group, Institute for Space Sciences, Bucharest, Romania.
    Fazakerley, Andrew
    Mullard Space Science Laboratory, University College London, Surrey, UK.
    Lucek, Elizabeth A.
    Space and Atmospheric Physics Group, London, UK.
    Spatiotemporal features of the auroral acceleration region as observed by Cluster2011Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, nr 12, s. A00K19-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A pair of negative electric potential structures associated with inverted-V aurora is investigated using electric and magnetic field, ion and electron data from the Cluster spacecraft, crossing the auroral acceleration region (AAR) at different altitudes above the Northern hemisphere midnight auroral oval. The spatial and temporal development of the acceleration structures is studied, given the magnetic conjunction opportunity and the one minute difference between the Cluster spacecraft crossings. The configuration allowed for estimation of characteristic times of development for the two structures and of the parallel electric field and potential drop for the more stable one. The first potential structure had a width of similar to 80 km (projected to the ionosphere) and was relatively short-lived, developing in less than 40 s and decaying in one minute. The parallel potential drop increased between altitudes of 1.13 R(E) and 1.3 R(E), whereas the acceleration potential above 1.3 R(E) remained almost unchanged during that time. This intensification occurred mainly after the time when the associated upward current had reached its maximum value. The second structure had a width of similar to 50 km and was subject to an increase by a factor of 3 of the parallel potential drop below 1.3 R(E), during about 40 s, after which it remained rather stable for one minute or more. Similarly here, the acceleration potential above 1.3 R(E) remained roughly unchanged. For the more stable second structure, an average parallel electric field between 1.13 and 1.3 R(E) could be estimated (similar to 0.56 mV/m). The conductance along the flux tube was also stable for one minute or more.

  • 171. SANDAHL, I
    et al.
    Lindqvist, Per-Arne
    KTH.
    Electron populations above the nightside auroral oval during magnetic quiet times1990Inngår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 38, nr 8, s. 1031-1049Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In several studies of particle morphology above the nightside auroral oval, the electrons have been divided into two separate spatial regions, often called the BPS (from "boundary plasma sheet") and the CPS (from "central plasma sheet") (Winningham et al., 1975, J. geophys. Res. 80, 3148). The names were derived from the source regions suggested by Winningham et al. In many cases this classification has worked well, but there are also many cases in which it has not. In this paper an alternative classification is proposed and explored by investigating the spatial distribution of electrons at altitudes between 2000 and 13,500 km, using particle spectrograms from the Viking satellite. A major difference between the newly proposed and the earlier classification is that spatial regions of populations may overlap in this new scheme. Electrons above the auroral oval could be divided into two populations. The first one is spatially unstructured and has a characteristic energy of a few kiloelectron volts. It is usually trapped in its equatorward part, while it is isotropic in its poleward part. The second one is spatially structured and normally has a characteristic energy of 100 eV or less. It is always present when there are signs of electron acceleration along magnetic field lines. The global distributions of both the structured and the unstructured electrons are ring-shaped. The two regions partially overlap, and the average latitude of the structured electrons is higher than the average latitude of the unstructured electrons. The majority of bright auroras appear in the region of overlap. The average poleward edge of the overlap region seems to coincide with the average poleward edge of region 1 field-aligned currents. We suggest that this boundary maps to the boundary between the central plasma sheet and the plasma sheet boundary layer. We also suggest that the sources for the region where only structured electrons are present are the low-latitude boundary layer and plasma sheet boundary layer. The conclusions concerning source regions are supported by mapping of the particle population regions into the equatorial plane of the magnetosphere using the Tsyganenko (1987, Planet. Space Sci. 35, 1347) magnetic field model. The average boundary between region 1 and region 2 field-aligned currents in the afternoon and evening is approximately at the average equatorward boundary of unstructured electrons. Through the midnight, morning and prenoon sectors it is at the average equatorward boundary of structured electrons.

  • 172. Sergeev, V. A.
    et al.
    Apatenkov, S. V.
    Nakamura, R.
    Baumjohann, W.
    Khotyaintsev, Y. V.
    Kauristie, K.
    van de Kamp, M.
    Burch, J. L.
    Ergun, R. E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Torbert, R.
    Russell, C. T.
    Giles, B. L.
    Substorm-Related Near-Earth Reconnection Surge: Combining Telescopic and Microscopic Views2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 12, s. 6239-6247Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A strong ~11-min-long surge of the lobe reconnection was observed during a substorm on the tailward side of the near-Earth neutral line. In the southern lobe near the reconnection separatrix the MMS spacecraft observed short-duration earthward electron beams providing the local Hall current, tailward propagating Alfven wave (AW) bursts with Poynting flux up to 10−4 W/m2, and large-amplitude E field spikes (e-holes) and low hybrid waves. The reconnection surge was accompanied by substorm current wedge formation and fast poleward expansion of auroral bulge-related westward electrojet in the conjugate ionosphere. During its meridional crossing above the expanding bulge the Metop-2 spacecraft observed an intense energetic precipitation spike near the expected X line foot point and confirmed the dipolarized character of magnetic field lines inside of the bulge. Globally the observed average reconnection rate (&lt;Ey &gt; ~3.3 mV/m) was sufficient to produce the magnetic flux increase in the bulge, associated with observed fast poleward expansion (about 6° latitude in 5 min).

  • 173. Stasiewicz, K
    et al.
    Gustafsson, G
    Marklund, Göran T.
    Lindqvist, Per-Arne
    KTH.
    Clemmons, J
    Zanetti, L
    Cavity resonators and Alfven resonance cones observed on Freja1997Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 102, nr A2, s. 2565-2575Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multiresolution wavelet analysis of magnetic field, electric field, and plasma density records taken on Freja during strong auroral events shows evidence for cavity Alfven resonators in the topside ionosphere. The cavity (or transverse) resonators consist of standing perpendicular wave modes which are trapped inside plasma cavities of different perpendicular scales. The smallest size cavities have perpendicular widths comparable to the electron skin depth, lambda(s) = 2 pi c/omega(pe), and are presumably associated with the resonance cones of Alfven waves launched by a magnetospheric source. The Alfven resonance cones (ARCs) carry intense field-aligned currents, support strong parallel electric fields and represent discharge and heating channels for auroral particles. We have made a detailed analysis of the electromagnetic properties of two singular auroral structures associated with ARCs. Field-aligned currents at the resonance structures reach intensities of 100-300 rho Am-2 in the upward and downward directions and are carried mainly by cold ionospheric plasma in both directions. The parallel electric field of ARCs is observed at amplitudes up to 100 mV/m, which is 2 orders of magnitude larger than expected for the unbounded Alfven waves. Field-aligned electron beams accelerated inside ARCs are observed to drive Langmuir waves with parallel electric field occasionally exceeding 1 V/m. One of the analyzed ARC structures has electromagnetic and particle properties characteristic of ''black aurora'' with electric field diverging from the center of the cavity; the other has converging electric field.

  • 174.
    Stawarz, J. E.
    et al.
    Imperial Coll London, Dept Phys, London, England..
    Eastwood, J. P.
    Imperial Coll London, Dept Phys, London, England..
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Burgess, D.
    Queen Mary Univ London, Sch Phys & Astron, London, England..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX USA.;Univ Texas San Antonio, San Antonio, TX USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Sorbonne Univ, CNRS, Ecole Polytech,Observ Paris,Lab Phys Plasmas, Paris, France..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Intense Electric Fields and Electron-Scale Substructure Within Magnetotail Flux Ropes as Revealed by the Magnetospheric Multiscale Mission2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 17, s. 8783-8792Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Three flux ropes associated with near-Earth magnetotail reconnection are analyzed using Magnetospheric Multiscale observations. The flux ropes are Earthward propagating with sizes from similar to 3 to 11 ion inertial lengths. Significantly different axial orientations are observed, suggesting spatiotemporal variability in the reconnection and/or flux rope dynamics. An electron-scale vortex, associated with one of the most intense electric fields (E) in the event, is observed within one of the flux ropes. This E is predominantly perpendicular to the magnetic field (B); the electron vortex is frozen-in with E x B drifting electrons carrying perpendicular current and causing a small-scale magnetic enhancement. The vortex is similar to 16 electron gyroradii in size perpendicular to B and potentially elongated parallel to B. The need to decouple the frozen-in vortical motion from the surrounding plasma implies a parallel E at the structure's ends. The formation of frozen-in electron vortices within reconnection-generated flux ropes may have implications for particle acceleration. Plain LanguageSummary The release of magnetic energy into particle motion through magnetic reconnection is a key driver of dynamics in the Earth's magnetosphere and other space plasmas. In order to understand how the released magnetic energy is distributed and ultimately heats the particles, a detailed examination of the structures formed by magnetic reconnection is necessary. One common structure produced by reconnection is a twisted magnetic field known as a flux rope. We use new data from the National Aeronautics and Space Administration's Magnetospheric Multiscale satellites to examine both the large-and small-scale properties of three flux ropes associated with a single reconnection event. The results reveal the intrinsic three-dimensional nature of the overall reconnection event, which may stem either from variability at the reconnection site and/or the subsequent dynamics of the structures after they form. Additionally, the high-resolution measurements reveal a new small-scale structure, namely, a vortex of electrons, inside of one of the flux ropes. The presence of such vortices may contribute to accelerating particles and points to the necessity of better understanding the substructure of flux ropes in order to characterize particle energization in magnetic reconnection.

  • 175.
    Stawarz, J. E.
    et al.
    Imperial Coll London, Dept Phys, London, England..
    Eastwood, J. P.
    Imperial Coll London, Dept Phys, London, England..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Gingell, I. L.
    Imperial Coll London, Dept Phys, London, England..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA.;Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Lab Phys Plasmas, CNRS, Ecole Polytech,Sorbonne Univ,Observ Paris, Paris, France..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Argall, M. R.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Fischer, D.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Franci, L.
    Queen Mary Univ London, Sch Phys & Astron, London, England..
    Properties of the Turbulence Associated with Electron-only Magnetic Reconnection in Earth's Magnetosheath2019Inngår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 877, nr 2, artikkel-id L37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Turbulent plasmas generate intense current structures, which have long been suggested as magnetic reconnection sites. Recent Magnetospheric Multiscale observations in Earth's magnetosheath revealed a novel form of reconnection where the dynamics only couple to electrons, without ion involvement. It was suggested that such dynamics were driven by magnetosheath turbulence. In this study, the fluctuations are examined to determine the properties of the turbulence and if a signature of reconnection is present in the turbulence statistics. The study reveals statistical properties consistent with plasma turbulence with a correlation length of similar to 10 ion inertial lengths. When reconnection is more prevalent, a steepening of the magnetic spectrum occurs at the length scale of the reconnecting current sheets. The statistics of intense currents suggest the prevalence of electron-scale current sheets favorable for electron reconnection. The results support the hypothesis that electron reconnection is driven by turbulence and highlight diagnostics that may provide insight into reconnection in other turbulent plasmas.

  • 176. Stawarz, J. E.
    et al.
    Eastwood, J. P.
    Varsani, A.
    Ergun, R. E.
    Shay, M. A.
    Nakamura, R.
    Phan, T. D.
    Burch, J. L.
    Gershman, D. J.
    Giles, B. L.
    Goodrich, K. A.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Russell, C. T.
    Strangeway, R. J.
    Torbert, R. B.
    Magnetospheric Multiscale analysis of intense field-aligned Poynting flux near the Earth's plasma sheet boundary2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 14, s. 7106-7113Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Magnetospheric Multiscale mission is employed to examine intense Poynting flux directed along the background magnetic field toward Earth, which reaches amplitudes of nearly 2 mW/m(2). The event is located within the plasma sheet but likely near the boundary at a geocentric distance of 9 RE in association with bulk flow signatures. The fluctuations have wavelengths perpendicular to the magnetic field of 124-264 km (compared to an ion gyroradius of 280 km), consistent with highly kinetic Alfven waves. While the wave vector remains highly perpendicular to the magnetic field, there is substantial variation of the direction in the perpendicular plane. The field-aligned Poynting flux may be associated with kinetic Alfven waves released along the separatrix by magnetotail reconnection and/or the radiation of waves excited by bursty bulk flow braking and may provide a means through which energy released by magnetic reconnection is transferred to the auroral region.

  • 177. Stawarz, J. E.
    et al.
    Eriksson, S.
    Wilder, F. D.
    Ergun, R. E.
    Schwartz, S. J.
    Pouquet, A.
    Burch, J. L.
    Giles, B. L.
    Khotyaintsev, Y.
    Le Contel, O.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Magnes, W.
    Pollock, C. J.
    Russell, C. T.
    Strangeway, R. J.
    Torbert, R. B.
    Avanov, L. A.
    Dorelli, J. C.
    Eastwood, J. P.
    Gershman, D. J.
    Goodrich, K. A.
    Malaspina, D. M.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Mirioni, L.
    Sturner, A. P.
    Observations of turbulence in a Kelvin-Helmholtz event on 8 September 2015 by the Magnetospheric Multiscale mission2016Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 11, s. 11021-11034Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spatial and high-time-resolution properties of the velocities, magnetic field, and 3-D electric field within plasma turbulence are examined observationally using data from the Magnetospheric Multiscale mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a first look at the properties of turbulence in the KHI. For the first time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra exhibit power law behavior with changes in slope near the ion gyrofrequency and lower hybrid frequency. The work provides the first observational evidence for turbulent intermittency and anisotropy consistent with quasi two-dimensional turbulence in association with the KHI. The behavior of kinetic-scale intermittency is found to have differences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics in the KHI.

  • 178.
    Steinvall, K.
    et al.
    Swedish Inst Space Phys, Uppsala, Sweden.;Uppsala Univ, Dept Phys & Astron, Uppsala, Sweden..
    Khotyaintsev, Yu. V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, Andris
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Multispacecraft Analysis of Electron Holes2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 1, s. 55-63Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron holes (EHs) are nonlinear electrostatic structures in plasmas. Most previous in situ studies of EHs have been limited to single- and two-spacecraft methods. We present statistics of EHs observed by Magnetospheric Multiscale on the magnetospheric side of the magnetopause during October 2016 when the spacecraft separation was around 6km. Each EH is observed by all four spacecraft, allowing EH properties to be determined with unprecedented accuracy. We find that the parallel length scale, l(vertical bar), scales with the Debye length. The EHs can be separated into three groups of speed and potential based on their coupling to ions. We present a method for calculating the perpendicular length scale, l. The method can be applied to a small subset of the observed EHs for which we find shapes ranging from almost spherical to more oblate. For the remaining EHs we use statistical arguments to find l/l(vertical bar)approximate to 5, implying dominance of oblate EHs. Plain Language Summary Electron holes are positively charged structures moving along the magnetic field and are frequently observed in space plasmas in relation to strong currents and electron beams. Electron holes interact with the plasma, leading to electron heating and scattering. In order to understand the effect of these electron holes, we need to accurately determine their properties, such as velocity, length scale, and potential. Most earlier studies have relied on single- or two-spacecraft methods to analyze electron holes. In this study we use the four satellites of the Magnetospheric Multiscale mission to analyze 236 electron holes with unprecedented accuracy. We find that the holes can be divided into three distinct groups with different properties. Additionally, we calculate the width of individual electron holes, finding that they are typically much wider than long, resembling pancakes.

  • 179. Tang, B. -B
    et al.
    Li, W. Y.
    Chinese Acad Sci, State Key Lab Space Weather, Natl Space Sci Ctr, Beijing, Peoples R China.;Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Rager, A. C.
    Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Wang, C.
    Chinese Acad Sci, State Key Lab Space Weather, Natl Space Sci Ctr, Beijing, Peoples R China.;Univ Chinese Acad Sci, Coll Earth & Planetary Sci, Beijing, Peoples R China..
    Khotyaintsev, Yu. V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, Toulouse, France..
    Hasegawa, H.
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Zhang, Y. -C
    Dai, L.
    Chinese Acad Sci, State Key Lab Space Weather, Natl Space Sci Ctr, Beijing, Peoples R China..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause: Magnetospheric Multiscale Observations2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 6, s. 3024-3032Artikkel i tidsskrift (Fagfellevurdert)
    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. 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.

  • 180.
    Tang, Binbin
    et al.
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Li, Wenya
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China.;Swedish Inst Space Phys, Uppsala, Sweden..
    Wang, Chi
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Dai, Lei
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Khotyaintsev, Yuri
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ergun, Robert
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Le Contel, Olivier
    Univ Paris Sud, UPMC Univ Paris 06, CNRS, Lab Phys Plasmas,Ecole Polytech,Observ Paris, Paris, France..
    Pollock, Craig
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Russell, Christopher
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Burch, James
    Southwest Res Inst, San Antonio, TX USA..
    Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin-Helmholtz waves2018Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, nr 3, s. 879-889Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report an ion-scale magnetic flux rope (the size of the flux rope is similar to 8.5 ion inertial lengths) at the trailing edge of Kelvin-Helmholtz (KH) waves observed by the Magnetospheric Multiscale (MMS) mission on 27 September 2016, which is likely generated by multiple X-line reconnection. The currents of this flux rope are highly filamentary: in the central flux rope, the current flows are mainly parallel to the magnetic field, supporting a local magnetic field increase at about 7 nT, while at the edges the current filaments are predominantly along the antiparallel direction, which induce an opposing field that causes a significant magnetic depression along the axis direction (> 20 nT), meaning the overall magnetic field of this flux rope is depressed compared to the ambient magnetic field. Thus, this flux rope, accompanied by the plasma thermal pressure enhancement in the center, is referred to as a crater type. Intense lower hybrid drift waves (LHDWs) are found at the magnetospheric edge of the flux rope, and the wave potential is estimated to be similar to 17% of the electron temperature. Though LHDWs may be stabilized by the mechanism of electron resonance broadening, these waves could still effectively enable diffusive electron transports in the cross-field direction, corresponding to a local density dip. This indicates LHDWs could play important roles in the evolution of crater flux ropes.

  • 181. Teh, W. -L
    et al.
    Nakamura, T. K. M.
    Nakamura, R.
    Baumjohann, W.
    Russell, C. T.
    Pollock, C.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R. E.
    Burch, J. L.
    Torbert, R. B.
    Giles, B. L.
    Evolution of a typical ion-scale magnetic flux rope caused by thermal pressure enhancement2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 2, s. 2040-2050Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With high time-resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion-scale magnetic flux ropes (similar to 5 and similar to 11 ion inertial length radius) separated by similar to 14 s are resolved. These two ion-scale flux ropes (FR1 and FR2) show non-frozen-in ion behavior and consist of a strong axial magnetic field at the reversal of the negative-then-positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater-like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force-free but the FR2 seems not. Moreover, the FR2 is time-dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann-Teller frame using the direct measured electric fields, while the FR1 is in quasi-steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater-like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope.

  • 182. Toledo-Redondo, Sergio
    et al.
    Andre, Mats
    Khotyaintsev, Yuri V.
    Lavraud, Benoit
    Vaivads, Andris
    Graham, Daniel B.
    Li, Wenya
    Perrone, Denise
    Fuselier, Stephen
    Gershman, Daniel J.
    Aunai, Nicolas
    Dargent, Jeremy
    Giles, Barbara
    Le Contel, Olivier
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, Robert E.
    Russell, Christopher T.
    Burch, James L.
    Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 9, s. 9396-9413Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10-25% of the energy spent by reconnection into ion heating went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely helium and oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization. Plain Language Summary The magnetic field of Earth creates a natural shield that isolates and protects us from the particles and fields coming from our star, the Sun. This natural shield is called the magnetosphere and is filled by plasma. The particles coming from the Sun form another plasma called the solar wind and are usually deviated around the magnetosphere. However, under certain circumstances these two plasmas can reconnect (magnetic reconnection), and part of the energy and mass of the two plasmas is interchanged. Magnetic reconnection is the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs to particles of very low energy (cold ions) of ionospheric origin when they reach the reconnecting boundary of the magnetosphere. It is found that they are energized and take an important part of the energy spent in reconnecting the plasmas. The plasma boundary develops spatial structures and emits waves that are able to heat the cold ions. Once heated, these cold ions irreversibly will escape the Earth's magnetosphere to never come back to Earth.

  • 183. Toledo-Redondo, Sergio
    et al.
    Andre, Mats
    Khotyaintsev, Yuri V.
    Vaivads, Andris
    Walsh, Andrew
    Li, Wenya
    Graham, Daniel B.
    Lavraud, Benoit
    Masson, Arnaud
    Aunai, Nicolas
    Divin, Andrey
    Dargent, Jeremy
    Fuselier, Stephen
    Gershman, Daniel J.
    Dorelli, John
    Giles, Barbara
    Avanov, Levon
    Pollock, Craig
    Saito, Yoshifumi
    Moore, Thomas E.
    Coffey, Victoria
    Chandler, Michael O.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Torbert, Roy
    Russell, Christopher T.
    Cold ion demagnetization near the X-line of magnetic reconnection2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 13, s. 6759-6767Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although the effects of magnetic reconnection in magnetospheres can be observed at planetary scales, reconnection is initiated at electron scales in a plasma. Surrounding the electron diffusion region, there is an Ion-Decoupling Region (IDR) of the size of the ion length scales (inertial length and gyroradius). Reconnection at the Earth's magnetopause often includes cold magnetospheric (few tens of eV), hot magnetospheric (10keV), and magnetosheath (1keV) ions, with different gyroradius length scales. We report observations of a subregion inside the IDR of the size of the cold ion population gyroradius (approximate to 15km) where the cold ions are demagnetized and accelerated parallel to the Hall electric field. Outside the subregion, cold ions follow the E x B motion together with electrons, while hot ions are demagnetized. We observe a sharp cold ion density gradient separating the two regions, which we identify as the cold and hot IDRs.

  • 184.
    Toledo-Redondo, Sergio
    et al.
    European Space Agcy, ESAC, Madrid, Spain..
    Dargent, Jeremy
    Univ Paris Sud, UPMC, CNRS, Ecole Polytech,Lab Plasma Phys, Paris, France.;Univ Toulouse, UPS, CNRS, Inst Rech Astrophys & Planetol,CNES, Toulouse, France..
    Aunai, Nicolas
    Univ Paris Sud, UPMC, CNRS, Ecole Polytech,Lab Plasma Phys, Paris, France..
    Lavraud, Benoit
    Univ Toulouse, UPS, CNRS, Inst Rech Astrophys & Planetol,CNES, Toulouse, France..
    Andre, Mats
    Swedish Inst Space Phys, Uppsala, Sweden..
    Li, Wenya
    Swedish Inst Space Phys, Uppsala, Sweden.;Chinese Acad Sci, State Key Lab Space Weather, Natl Space Sci Ctr, Beijing, Peoples R China..
    Giles, Barbara
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ergun, Robert E.
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO USA..
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Perpendicular Current Reduction Caused by Cold Ions of Ionospheric Origin in Magnetic Reconnection at the Magnetopause: Particle-in-Cell Simulations and Spacecraft Observations2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 19, s. 10033-10042Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cold ions of ionospheric origin are present throughout the Earth's magnetosphere, including the dayside magnetopause, where they modify the properties of magnetic reconnection, a major coupling mechanism at work between the magnetosheath and the magnetosphere. We present Magnetospheric MultiScale (MMS) spacecraft observations of the reconnecting magnetopause with different amounts of cold ions and show that their presence reduces the Hall term in the Ohm's law. Then, we compare two particle-in-cell simulations, with and without cold ions on the magnetospheric side. The cold ions remain magnetized inside the magnetospheric separatrix region, leading to the reduction of the perpendicular currents associated with the Hall effect. Moreover, this reduction is proportional to the relative number density of cold ions. And finally, the Hall electric field peak is reduced along the magnetospheric separatrix owing to cold ions. This should have an effect on energy conversion by reconnection from electromagnetic fields to kinetic energy of the particles. Plain Language Summary The magnetic field of Earth creates a natural boundary that isolates and protects us from the particles and fields coming from the Sun, typically known as the solar wind. This natural shield is called the magnetosphere and is filled by plasma. The particles are coming from the solar wind and are usually deviated around the magnetosphere. However, various mechanisms are capable of interconnecting these two regions of plasma, permitting the exchange of mass and energy. Magnetic reconnection is a primary coupling mechanism and the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs when particles of very low energy (cold ions) of ionospheric origin reach the reconnecting boundary between the solar wind and the magnetosphere. We use both spacecraft observations and numerical simulations, and we find that they modify the way reconnection operates, by reducing the currents carried by electrons. The electric fields associated with energization of particles are reduced as well under the presence of cold ions coming from the ionosphere.

  • 185. Tong, Y.
    et al.
    Vasko, I.
    Mozer, F. S.
    Bale, S. D.
    Roth, I.
    Artemyev, A. V.
    Ergun, R.
    Giles, B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, C. T.
    Strangeway, R.
    Torbert, R. B.
    Simultaneous Multispacecraft Probing of Electron Phase Space Holes2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 21, s. 11,513-11,519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a series of electron holes observed simultaneously on four Magnetospheric Multiscale spacecraft in the plasma sheet boundary layer. The multispacecraft probing shows that the electron holes propagated quasi-parallel to the local magnetic field with velocities of a few thousand kilometers per second with parallel spatial scales of a few kilometers (a few Debye lengths). The simultaneous multispacecraft probing allows analyzing the 3-D configuration of the electron holes. We estimate the electric field gradients and charge densities associated with the electrons holes. The electric fields are fit to simple 3-D electron hole models to estimate their perpendicular scales and demonstrate that the electron holes were generally not axially symmetric with respect to the local magnetic field. We emphasize that most of the electron holes had a complicated structure not reproduced by the simple models widely used in single-spacecraft studies.

  • 186. Torbert, R. B.
    et al.
    Burch, J. L.
    Argall, M. R.
    Alm, L.
    Farrugia, C. J.
    Forbes, T. G.
    Giles, B. L.
    Rager, A.
    Dorelli, J.
    Strangeway, R. J.
    Ergun, R. E.
    Wilder, F. D.
    Ahmadi, N.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Khotyaintsev, Y.
    Structure and Dissipation Characteristics of an Electron Diffusion Region Observed by MMS During a Rapid, Normal-Incidence Magnetopause Crossing2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 12, s. 11901-11916Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On 22 October 2016, the Magnetospheric Multiscale (MMS) spacecraft encountered the electron diffusion region (EDR) when the magnetosheath field was southward, and there were signatures of fast reconnection, including flow jets, Hall fields, and large power dissipation. One rapid, normal-incidence crossing, during which the EDR structure was almost stationary in the boundary frame, provided an opportunity to observe the spatial structure for the zero guide field case of magnetic reconnection. The reconnection electric field was determined unambiguously to be 2-3 mV/m. There were clear signals of fluctuating parallel electric fields, up to 6 mV/m on the magnetosphere side of the diffusion region, associated with a Hall-like parallel current feature on the electron scale. The width of the main EDR structure was determined to be similar to 2 km (1.8 de). Although the MMS spacecraft were in their closest tetrahedral separation of similar to 8 km, the divergences and curls for these thin current structures could therefore not be computed in the usual manner. A method is developed to determine these quantities on a much smaller scale and applied to compute the normal component of terms in the generalized Ohm's law for the positions of each individual spacecraft (not a barocentric average). Although the gradient pressure term has a qualitative dependence that follows the observed variation of E + Ve x B, the quantitative magnitude of these terms differs by more than a factor of 2, which is shown to be greater than the respective errors. Thus, future research is required to find the manner in which Ohm's law is balanced. Plain Language Summary The Magnetospheric Multiscale (MMS) spacecraft observed the spatial structure of the region where magnetic energy is converted to particle flows and heat. New features of currents and fields parallel to the magnetic field are analyzed. Some discrepancies with present computer simulations are found within this region.

  • 187. Torbert, R. B.
    et al.
    Burch, J. L.
    Giles, B. L.
    Gershman, D.
    Pollock, C. J.
    Dorelli, J.
    Avanov, L.
    Argall, M. R.
    Shuster, J.
    Strangeway, R. J.
    Russell, C. T.
    Ergun, R. E.
    Wilder, F. D.
    Goodrich, K.
    Faith, H. A.
    Farrugia, C. J.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Phan, T.
    Khotyaintsev, Y.
    Moore, T. E.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Daughton, W.
    Magnes, W.
    Kletzing, C. A.
    Bounds, S.
    Estimates of terms in Ohm's law during an encounter with an electron diffusion region2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 12, s. 5918-5925Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present measurements from the Magnetospheric Multiscale (MMS) mission taken during a reconnection event on the dayside magnetopause which includes a passage through an electron diffusion region (EDR). The four MMS satellites were separated by about 10 km such that estimates of gradients and divergences allow a reasonable estimate of terms in the generalized Ohm's law, which is key to investigating the energy dissipation during reconnection. The strength and character of dissipation mechanisms determines how magnetic energy is released. We show that both electron pressure gradients and electron inertial effects are important, but not the only participants in reconnection near EDRs, since there are residuals of a few mV/m (similar to 30-50%) of E + U-e x B (from the sum of these two terms) during the encounters. These results are compared to a simulation, which exhibits many of the observed features, but where relatively little residual is present.

  • 188.
    Torbert, R. B.
    et al.
    Univ New Hampshire, Durham, NH 03824 USA.;Southwest Res Inst SwRI, San Antonio, TX 78228 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Saito, Y.
    et al,
    Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space2018Inngår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, nr 6421, s. 1391-+Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth's magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth's magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvenic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.

  • 189. Torbert, R. B.
    et al.
    Russell, C. T.
    Magnes, W.
    Ergun, R. E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    LeContel, O.
    Vaith, H.
    Macri, J.
    Myers, S.
    Rau, D.
    Needell, J.
    King, B.
    Granoff, M.
    Chutter, M.
    Dors, I.
    Olsson, Göran F.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Khotyaintsev, Y. V.
    Eriksson, A.
    Kletzing, C. A.
    Bounds, S.
    Anderson, B.
    Baumjohann, W.
    Steller, M.
    Bromund, K.
    Le, Guan
    Nakamura, R.
    Strangeway, R. J.
    Leinweber, H. K.
    Tucker, S.
    Westfall, J.
    Fischer, D.
    Plaschke, F.
    Porter, J.
    Lappalainen, K.
    The FIELDS Instrument Suite on MMS: Scientific Objectives, Measurements, and Data Products2016Inngår i: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 199, nr 1-4, s. 105-135Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission provides comprehensive measurements of the full vector magnetic and electric fields in the reconnection regions investigated by MMS, including the dayside magnetopause and the night-side magnetotail acceleration regions out to 25 Re. Six sensors on each of the four MMS spacecraft provide overlapping measurements of these fields with sensitive cross-calibrations both before and after launch. The FIELDS magnetic sensors consist of redundant flux-gate magnetometers (AFG and DFG) over the frequency range from DC to 64 Hz, a search coil magnetometer (SCM) providing AC measurements over the full whistler mode spectrum expected to be seen on MMS, and an Electron Drift Instrument (EDI) that calibrates offsets for the magnetometers. The FIELDS three-axis electric field measurements are provided by two sets of biased double-probe sensors (SDP and ADP) operating in a highly symmetric spacecraft environment to reduce significantly electrostatic errors. These sensors are complemented with the EDI electric measurements that are free from all local spacecraft perturbations. Cross-calibrated vector electric field measurements are thus produced from DC to 100 kHz, well beyond the upper hybrid resonance whose frequency provides an accurate determination of the local electron density. Due to its very large geometric factor, EDI also provides very high time resolution (similar to 1 ms) ambient electron flux measurements at a few selected energies near 1 keV. This paper provides an overview of the FIELDS suite, its science objectives and measurement requirements, and its performance as verified in calibration and cross-calibration procedures that result in anticipated errors less than 0.1 nT in B and 0.5 mV/m in E. Summaries of data products that result from FIELDS are also described, as well as algorithms for cross-calibration. Details of the design and performance characteristics of AFG/DFG, SCM, ADP, SDP, and EDI are provided in five companion papers.

  • 190. Torkar, K.
    et al.
    Eriksson, A. I.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Steiger, W.
    Long-Term Study of Active Spacecraft Potential Control2008Inngår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, nr 5, s. 2294-2300Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Emitters based on the liquid metal ion source principle have been operating on the Cluster spacecraft between 2000 and 2004, in order to control the spacecraft potential. The resulting reduction of positive spacecraft potential reduces perturbations to the plasma measurements on board. Ion currents up to 40 [LA have been applied, which reduced the energy band in which photoelectrons disturb the plasma electron measurements to values close to the lower detection limit of the instrument. The experience with this method, meanwhile, covers both the maximum and minimum of the present solar cycle and allows one to study the variations of photoemission and other long-term trends and their effects on the measurements. A long-term trend of the controlled spacecraft potential is indeed observed. In addition, it appears that reconstruction of the uncontrolled spacecraft potential from the controlled one is possible if certain conditions are fulfilled. Spacecraft potential control can thereby improve the plasma measurements while still allowing one to estimate the total plasma density from the residual potential.

  • 191. Torkar, K.
    et al.
    Nakamura, R.
    Andriopoulou, M.
    Giles, B. L.
    Jeszenszky, H.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Torbert, R. B.
    Influence of the Ambient Electric Field on Measurements of the Actively Controlled Spacecraft Potential by MMS2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 12, s. 12019-12030Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Space missions with sophisticated plasma instrumentation such as Magnetospheric Multiscale, which employs four satellites to explore near-Earth space benefit from a low electric potential of the spacecraft, to improve the plasma measurements and therefore carry instruments to actively control the potential by means of ion beams. Without control, the potential varies in anticorrelation with plasma density and temperature to maintain an equilibrium between the plasma current and the one of photoelectrons produced at the surface and overcoming the potential barrier. A drawback of the controlled, almost constant potential is the difficulty to use it as convenient estimator for plasma density. This paper identifies a correlation between the spacecraft potential and the ambient electric field, both measured by double probes mounted at the end of wire booms, as the main responsible for artifacts in the potential data besides the known effect of the variable photoelectron production due to changing illumination of the surface. It is shown that the effect of density variations is too weak to explain the observed correlation with the electric field and that a correction of the artifacts can be achieved to enable the reconstruction of the uncontrolled potential and plasma density in turn. Two possible mechanisms are discussed: the asymmetry of the current-voltage characteristic determining the probe to plasma potential and the fact that a large equipotential structure embedded in an electric field results in asymmetries of both the emission and spatial distribution of photoelectrons, which results in an increase of the spacecraft potential.

  • 192.
    Torkar, K.
    et al.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Wellenzohn, S.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Jeszenszky, H.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Improved Determination of Plasma Density Based on Spacecraft Potential of the Magnetospheric Multiscale Mission Under Active Potential Control2019Inngår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 47, nr 8, s. 3636-3647Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current-voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission.

  • 193. Varsani, A.
    et al.
    Nakamura, R.
    Sergeev, V. A.
    Baumjohann, W.
    Owen, C. J.
    Petrukovich, A. A.
    Yao, Z.
    Nakamura, T. K. M.
    Kubyshkina, M. V.
    Sotirelis, T.
    Burch, J. L.
    Genestreti, K. J.
    Voeroes, Z.
    Andriopoulou, M.
    Gershman, D. J.
    Avanov, L. A.
    Magnes, W.
    Russell, C. T.
    Plaschke, F.
    Khotyaintsev, Y. V.
    Giles, B. L.
    Coffey, V. N.
    Dorelli, J. C.
    Strangeway, R. J.
    Torbert, R. B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R.
    Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 11, s. 10891-10909Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high-energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X-line was located relatively close to the Earth, approximately at 16-18 R-E.

  • 194.
    Vasko, I. Y.
    et al.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Mozer, F. S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Krasnoselskikh, V. V.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Orleans, LPC2E, Orleans, France..
    Artemyev, A. V.
    Univ Calif Los Angeles, Inst Geophys & Planetary Sci, Los Angeles, CA 90024 USA.;Russian Acad Sci, Space Res Inst, Moscow, Russia..
    Agapitov, O. V.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Bale, S. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Avanov, L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Ergun, R.
    Univ Colorado, Boulder, CO 80309 USA..
    Giles, B.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lindqvist, Per-Arne
    KTH.
    Russell, C. T.
    Univ Calif Los Angeles, Inst Geophys & Planetary Sci, Los Angeles, CA 90024 USA..
    Strangeway, R.
    Univ Calif Los Angeles, Inst Geophys & Planetary Sci, Los Angeles, CA 90024 USA..
    Torbert, R.
    Univ New Hampshire, Durham, NH 03824 USA..
    Solitary Waves Across Supercritical Quasi-Perpendicular Shocks2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 12, s. 5809-5817Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider intense electrostatic solitary waves (ESW) observed in a supercritical quasi-perpendicular Earth's bow shock crossing by the Magnetospheric Multiscale Mission. The ESW have spatial scales of a few tens of meters (a few Debye lengths) and propagate oblique to a local quasi-static magnetic field with velocities from a few tens to a few hundred kilometers per second in the spacecraft frame. Because the ESW spatial scales are comparable to the separation between voltage-sensitive probes, correction factors are used to compute the ESW electric fields. The ESW have electric fields with amplitudes exceeding 600mV/m (oriented oblique to the local magnetic field) and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature. The negative electrostatic potentials indicate that the ESW are not electron phase space holes, while interpretation in terms of ions phase space holes is also questionable. Whatever is their nature, we show that due to the oblique electric field orientation the ESW are capable of efficient pitch-angle scattering and isotropization of thermal electrons. Due to the negative electrostatic potentials the ESW Fermi reflects a significant fraction of the thermal electrons streaming from upstream (downstream) back to upstream (downstream) region, thereby affecting the shock dynamics. The role of the ESW in electron heating is discussed. Plain Language Summary Processes governing electron thermalization across shock waves are not entirely understood. The high resolution particle and 3-D electric field measurements provided by the Magnetospheric Multiscale Mission make it possible to study the Earth's bow shock that is an excellent laboratory for addressing the electron thermalization across supercritical shock waves. Previous observations showed that electron heating across the bow shock is generally governed by macroscopic cross-shock electrostatic field. On the other hand, the role of the turbulence observed across the bow shock in the electron thermalization has remained unclear. In this letter we consider a particular bow shock crossing by the Magnetospheric Multiscale Mission and focus on the role of the high amplitude electrostatic solitary waves in the electron thermalization process. We accurately estimate the electrostatic solitary wave parameters and show that due to electric fields oriented oblique to a local DC magnetic field and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature, these Debye-scale structures are capable of efficient pitch angle scattering, Fermi reflection, and isotropization of thermal electrons.

  • 195.
    Vaverka, Jakub
    et al.
    Umea Univ, Dept Phys, Umea, Sweden.;Natl Inst Polar Res, Tachikawa, Tokyo, Japan.;Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic..
    Nakamura, Takuji
    Natl Inst Polar Res, Tachikawa, Tokyo, Japan..
    Kero, Johan
    Swedish Inst Space Phys, Kiruna, Sweden..
    Mann, Ingrid
    Arctic Univ Norway, Tromso, Norway..
    De Spiegeleer, Alexandre
    Umea Univ, Dept Phys, Umea, Sweden..
    Hamrin, Maria
    Umea Univ, Dept Phys, Umea, Sweden..
    Norberg, Carol
    Umea Univ, Dept Phys, Umea, Sweden.;Swedish Inst Space Phys, Kiruna, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Pellinen-Wannberg, Asta
    Umea Univ, Dept Phys, Umea, Sweden.;Swedish Inst Space Phys, Kiruna, Sweden..
    Comparison of Dust Impact and Solitary Wave Signatures Detected by Multiple Electric Field Antennas Onboard the MMS Spacecraft2018Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 8, s. 6119-6129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dust impact detection by electric field instruments is a relatively new method. However, the influence of dust impacts on electric field measurements is not completely understood and explained. A better understanding is very important for reliable dust impact identification, especially in environments with low dust impact rate. Using data from Earth-orbiting Magnetospheric Multiscale mission (MMS) spacecraft, we present a study of various pulses detected simultaneously by multiple electric field antennas in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations. The study includes data obtained during an impact of a millimeter-sized object. We show that the identification of dust impacts by a single antenna is a very challenging issue in environments where solitary waves are commonly present and that some pulses can be easily misinterpreted as dust impacts. We used data from multiple antennas to distinguish between changes in the spacecraft potential (dust impact) and structures in the ambient plasma or electric field. Our results indicate that an impact cloud is in some cases able to influence the potential of the electric field antenna during its expansion.

  • 196. Vines, S. K.
    et al.
    Allen, R. C.
    Anderson, B. J.
    Engebretson, M. J.
    Fuselier, S. A.
    Russell, C. T.
    Strangeway, R. J.
    Ergun, R. E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Torbert, R. B.
    Burch, J. L.
    EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 11, s. 5707-5716Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electromagnetic ion cyclotron (EMIC) waves at large L shells were observed away from the magnetic equator by the Magnetospheric MultiScale (MMS) mission nearly continuously for over four hours on 28 October 2015. During this event, the wave Poynting vector direction systematically changed from parallel to the magnetic field (toward the equator), to bidirectional, to antiparallel (away from the equator). These changes coincide with the shift in the location of the minimum in the magnetic field in the southern hemisphere from poleward to equatorward of MMS. The local plasma conditions measured with the EMIC waves also suggest that the outer magnetospheric region sampled during this event was generally unstable to EMIC wave growth. Together, these observations indicate that the bidirectionally propagating wave packets were not a result of reflection at high latitudes but that MMS passed through an off-equator EMIC wave source region associated with the local minimum in the magnetic field.

  • 197. Vines, S. K.
    et al.
    Fuselier, S. A.
    Trattner, K. J.
    Burch, J. L.
    Allen, R. C.
    Petrinec, S. M.
    Anderson, B. J.
    Webster, J. M.
    Ergun, R. E.
    Giles, B. L.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Russell, C. T.
    Magnetospheric Ion Evolution Across the Low-Latitude Boundary Layer Separatrix2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 10, s. 10247-10262Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On 20 September 2015, the Magnetospheric Multiscale (MMS) spacecraft crossed the dusk magnetopause after a compression of the magnetosphere. Enhanced densities and fluxes of both colder (≤10 eV) and hotter (&gt;1 keV) magnetospheric and magnetosheath heavy ion species were observed reaching the magnetopause. The evolution of the velocity distributions for H+, He+, and O+ measured by the Hot Plasma Composition Analyzer on MMS during this magnetopause crossing is presented. In particular, this study focuses on the changes in the species' distribution functions as MMS passes from the magnetosphere through the electron edge of the low-latitude boundary layer (LLBL) separatrix and then into the LLBL. Two types of processes are suggested to play a role in the heating of colder magnetospheric ions across the LLBL separatrix in the region between the separatrix and the electron and ion edges of the LLBL. One mechanism leads to the formation and enhancement of ring distributions in this layer of the LLBL as the magnetospheric ions propagate across the separatrix. A second mechanism leading first to perpendicular heating and then to parallel heating of colder protons may arise from a possible two-stream instability as the magnetospheric ions first encounter the warmer magnetosheath electrons in the electron layer and then the warmer magnetosheath ions between the electron and ion edges of the LLBL separatrix. Perpendicular heating of He+ and O+ is seen more so in the main reconnection exhaust, due to nonadiabatic behavior of these ions as they are accelerated up to the bulk flow speed.

  • 198. VOGELSANG, H
    et al.
    LUHR, H
    VOELKER, H
    WOCH, J
    BOSINGER, T
    POTEMRA, TA
    Lindqvist, Per-Arne
    KTH.
    An ionospheric travelling convection vortex event observed by ground‐based magnetometers and by Viking1993Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 20, nr 21, s. 2343-2346Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A transient ionospheric travelling convection vortex (ITCV) event was recorded by the EISCAT magnetometer cross in northern Scandinavia on April 21, 1986 around 8:40 MLT. Simultaneously, the near-conjugate satellite VIKING observed strong magnetic and electric field variations on closed magnetic field lines. The signatures seen by the spacecraft are consistent with a passage through two oppositely directed field-aligned current tubes. The total upward and downward currents turned out to be matched within a region of approximately 1000 km in the ionosphere. Because of the close spatial and temporal proximity of both observations we interpret the field-aligned currents as being associated with the ITCV. This is the first time that in-situ measurements of the currents connecting the ITCV to the source region close to the magnetopause have been published. Both the current density and the dimensions of the current tubes could be estimated here.

  • 199. Voros, Z.
    et al.
    Yordanova, E.
    Varsani, A.
    Genestreti, K. J.
    Khotyaintsev, Yu. V.
    Li, W.
    Graham, D. B.
    Norgren, C.
    Nakamura, R.
    Narita, Y.
    Plaschke, F.
    Magnes, W.
    Baumjohann, W.
    Fischer, D.
    Vaivads, A.
    Eriksson, E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R. E.
    Leitner, M.
    Leubner, M. P.
    Strangeway, R. J.
    Le Contel, O.
    Pollock, C.
    Giles, B. J.
    Torbert, R. B.
    Burch, J. L.
    Avanov, L. A.
    Dorelli, J. C.
    Gershman, D. J.
    Paterson, W. R.
    Lavraud, B.
    Saito, Y.
    MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath2017Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 11, s. 11442-11467Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi-parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid-scale and kinetic-scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent-like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined.

  • 200.
    Wahlund, Jan-Erik
    et al.
    Swedish Institute of Space Physics, Uppsala.
    Blomberg, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Morooka, Michiko
    Swedish Institute of Space Physics, Uppsala.
    André, Mats
    Swedish Institute of Space Physics, Uppsala.
    Eriksson, Anders
    Swedish Institute of Space Physics, Uppsala.
    Cumnock, Judy
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Cold Plasma Diagnostics in the Jovian System: Brief Scientific Case and Instrumentation Overview2006Inngår i: Proceedings of the 6th IAA International Conference on Low-Cost Planetary Missions, 2006, s. 341-346Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The Jovian magnetosphere equatorial region is filled with cold dense plasma that in a broad sense co-rotate with its magnetic field. The volcanic moon Io, which expels sodium, sulphur and oxygen containing species, dominates as a source for this cold plasma. The three icy Galilean moons (Callisto, Ganymede, and Europa) also contribute with water group and oxygen ions.

    All the Galilean moons have thin atmospheres with residence times of a few days at most. Their ionized ionospheric components interact dynamically with the co-rotating magnetosphere of Jupiter and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. On these moons the surface interactions with the space environment determine their atmospheric and ionospheric properties.

    The range of processes associated with the Jovian magnetospheric interaction with the Galilean moons, where the cold dense plasma expelled from these moons play a key role, are not well understood. Conversely, the volatile material expelled from their interiors is important for our understanding of the Jovian magnetosphere dynamics and energy transfer. A Langmuir probe investigation, giving in-situ plasma density, temperatures, UV intensity and plasma speed with high time resolution, would be a most valuable component for future payloads to the Jupiter system. Recent developments in low-mass instrumentation facilitate Langmuir probe in situ measurements on such missions.

12345 151 - 200 of 220
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf