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  • 1. Aikio, A. T.
    et al.
    Pitkanen, T.
    Fontaine, D.
    Dandouras, I.
    Amm, O.
    Kozlovsky, A.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fazakerley, A.
    EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 1, p. 87-105Article in journal (Refereed)
    Abstract [en]

    The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromso (66.6 degrees cgmLat) and Longyearbyen (75.2 degrees cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5 degrees cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 R-E mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2 degrees during similar to 5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.

  • 2.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Space and Plasma Physics.
    Vaivads, Andris
    Buchert, Stephan C.
    Fazakerley, A. N.
    Lahiff, A.
    Thin electron-scale layers at the magnetopause2004In: Geophys. Res. Lett., Vol. 31, p. L03803-Article in journal (Refereed)
  • 3.
    André, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yu V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Laitinen, Tiera V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nilsson, H.
    Stenberg, G.
    Fazakerley, A.
    Trotignon, J. G.
    Magnetic reconnection and cold plasma at the magnetopause2010In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, no 22, p. L22108-Article in journal (Refereed)
    Abstract [en]

    We report on detailed observations by the four Cluster spacecraft of magnetic reconnection and a Flux Transfer Event (FTE) at the magnetopause. We detect cold (eV) plasma at the magnetopause with two independent methods. We show that the cold ions can be essential for the electric field normal to the current sheet in the separatrix region at the edge of the FTE and for the associated acceleration of ions from the magnetosphere into the reconnection jet. The cold ions have small enough gyroradii to drift inside the limited separatrix region and the normal electric field can be balanced by this drift, E approximate to -v x B. The separatrix region also includes cold accelerated electrons, as part of the reconnection current circuit.

  • 4. Aunai, N.
    et al.
    Retino, A.
    Belmont, G.
    Smets, R.
    Lavraud, B.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    The proton pressure tensor as a new proxy of the proton decoupling region in collisionless magnetic reconnection2011In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 29, no 9, p. 1571-1579Article in journal (Refereed)
    Abstract [en]

    Cluster data is analyzed to test the proton pressure tensor variations as a proxy of the proton decoupling region in collisionless magnetic reconnection. The Hall electric potential well created in the proton decoupling region results in bounce trajectories of the protons which appears as a characteristic variation of one of the in-plane off-diagonal components of the proton pressure tensor in this region. The event studied in this paper is found to be consistent with classical Hall field signatures with a possible 20% guide field. Moreover, correlations between this pressure tensor component, magnetic field and bulk flow are proposed and validated, together with the expected counterstreaming proton distribution functions.

  • 5.
    Backrud, Marie
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    André, Mats
    Balogh, André
    Buchert, Stephan
    Cornilleau-Wehrlin, Nicole
    Vaivads, Andris
    Identification of Broadband Waves Above the Auroral Acceleration Region: CLUSTER Observations2004In: Annales Geophysicae, ISSN 0992-7689, Vol. 22, no 12, p. 14-Article in journal (Refereed)
  • 6.
    Backrud, Marie
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Space and Plasma Physics.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Space and Plasma Physics.
    Wahlund, Jan-Erik
    Balogh, A.
    Buchert, Stephan
    Cornilleau-Wehrlin, Nicolle
    Vaivads, Andris
    Identification of broad-band waves above the auroral acceleration region: Cluster observations2004In: Ann. Geophys., Vol. 22, p. 4203-4216Article in journal (Refereed)
  • 7.
    Backrud, Marie
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Tjulin, Anders
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Fazakerley, Andrew
    Interferometric Identification of Ion Acoustic Broadband Waves in the Auroral Region: CLUSTER Observations2005In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 21Article in journal (Refereed)
    Abstract [en]

    [1] We determine the phase velocity and k vector for parallel and oblique broadband extremely low frequency, ELF, waves on nightside auroral magnetic field lines at altitudes around 4.6 RE. We use internal burst mode data from the EFW electric field and wave instrument onboard the Cluster spacecraft to retrieve phase differences between the four probes of the instrument. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength obtained from interferometry is around the proton gyro radius and always larger than the Debye length. We find that in regions with essentially no suprathermal electrons above a few tens of eV the observed broadband waves above the proton gyro frequency are consistent with upgoing ion acoustic and oblique ion acoustic waves.

  • 8.
    Bale, S. D.
    et al.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Goetz, K.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Harvey, P. R.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Turin, P.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Bonnell, J. W.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Dudok de Wit, T.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    MacDowall, R. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pulupa, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Bolton, M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Bougeret, J. -L
    Bowen, T. A.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Burgess, D.
    Queen Mary Univ London, Astron Unit, London, England..
    Cattell, C. A.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Chandran, B. D. G.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Chaston, C. C.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Chen, C. H. K.
    Imperial Coll, Dept Phys, London, England..
    Choi, M. K.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Connerney, J. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Cranmer, S.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Diaz-Aguado, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Donakowski, W.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Drake, J. F.
    Univ Maryland, Dept Phys, College Pk, MD 20742 USA..
    Farrell, W. M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Fergeau, P.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Fermin, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Fischer, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Fox, N.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Glaser, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Goldstein, M.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gordon, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Hanson, E.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Harris, S. E.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Hayes, L. M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Hinze, J. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Hollweg, J. V.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Horbury, T. S.
    Imperial Coll, Dept Phys, London, England..
    Howard, R. A.
    Naval Res Lab, Washington, DC 20375 USA..
    Hoxie, V.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Jannet, G.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Karlsson, M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Kasper, J. C.
    Univ Michigan, Ann Arbor, MI 48109 USA..
    Kellogg, P. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Kien, M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Klimchuk, J. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Krasnoselskikh, V. V.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Krucker, S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Lynch, J. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Maksimovic, M.
    Observ Paris, LESIA, Meudon, France..
    Malaspina, D. M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Marker, S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Martin, P.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Martinez-Oliveros, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    McCauley, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    McComas, D. J.
    Southwest Res Inst, San Antonio, TX USA..
    McDonald, T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Meyer-Vernet, N.
    Observ Paris, LESIA, Meudon, France..
    Moncuquet, M.
    Observ Paris, LESIA, Meudon, France..
    Monson, S. J.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    Mozer, F. S.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Murphy, S. D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Odom, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Oliverson, R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Olson, J.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Parker, E. N.
    Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA..
    Pankow, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Phan, T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Quataert, E.
    Univ Calif Berkeley, Dept Astron, 601 Campbell Hall, Berkeley, CA 94720 USA..
    Quinn, T.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Ruplin, S. W.
    Praxis Studios, Brooklyn, NY USA..
    Salem, C.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Seitz, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Sheppard, D. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Siy, A.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Stevens, K.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Summers, D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Szabo, A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Timofeeva, M.
    CNRS, LPC2E, 3A Ave Rech Sci, Orleans, France..
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Velli, M.
    UCLA, Earth Planetary & Space Sci, Los Angeles, CA USA..
    Yehle, A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Werthimer, D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Wygant, J. R.
    Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA..
    The FIELDS Instrument Suite for Solar Probe Plus2016In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 204, no 1-4, p. 49-82Article, review/survey (Refereed)
    Abstract [en]

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

  • 9. Baumjohann, W.
    et al.
    Roux, A.
    Le Contel, O.
    Nakamura, R.
    Birn, J.
    Hoshino, M.
    Lui, A. T. Y.
    Owen, C. J.
    Sauvaud, J. -A
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fontaine, D.
    Runov, A.
    Dynamics of thin current sheets: Cluster observations2007In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 25, no 6, p. 1365-1389Article, review/survey (Refereed)
    Abstract [en]

    The paper tries to sort out the specific signatures of the Near Earth Neutral Line (NENL) and the Current Disruption (CD) models. and looks for these signatures in Cluster data from two events. For both events transient magnetic si-natures are observed, together with fast ion flows. In the simplest form of NENL scenario, with a large-scale two-dimensional reconnection site, quasi-invariance along Y is expected. Thus the magnetic signatures in the S/C frame are interpreted as relative motions, along the X or Z direction, of a quasi-steady X-line, with respect to the S/C. In the simplest form of CD scenario an azimuthal modulation is expected. Hence the signatures in the S/C frame are interpreted as signatures of azimuthally (along Y) moving current system associated with low frequency fluctuations of J(y) and the corresponding field-aligned currents Event I covers a pseudo-breakup, developing only at high latitudes. First, a thin (H approximate to 2000Km approximate to 2 rho(i), with pi the ion gyroradius) Current Sheet (CS) is found to be quiet. A slightly thinner CS (H approximate to 1000-2000 km approximate to 1-2 rho(i)), crossed about 30 min later, is found to be active. with fast earthward ion flow bursts (300-600 km/s) and simultaneous large amplitude fluctuations (delta B/B similar to 1). In the quiet CS the current density J(y) is carried by ions. Conversely, in the active CS ions are moving eastward; the westward current is carried by electrons that move eastward, faster than ions. Similarly, the velocity of earthward flows (300-600 km/s), observed during the active period. maximizes near or at the CS center. During the active phase of Event I no signature of the crossing of an X-line is identified, but an X-line located beyond Cluster could account for the observed ion flows, provided that it is active for at least 20 min. Ion flow bursts can also be due to CD and to the corresponding dipolarizations which are associated with changes in the current density. Yet their durations are shorter than the duration of the active period. While the overall partial derivative Bz/partial derivative t is too weak to accelerate ions up to the observed velocities, short duration partial derivative B-z/partial derivative t can produce the azimuthal electric field requested to account for the observed ion flow bursts. The corresponding large amplitude perturbations are shown to move eastward. which suggests that the reduction in the tail current could be achieved via a series of eastward traveling partial dipolarisations/CD. The second event is much more active than the first one. The observed flapping of the CS corresponds to an azimuthally propagating wave. A reversal in the proton flow velocity, from 1000 to + 1000 km/s, is measured by CODIF. The overall flow reversal, the associated change in the sign of B-z and the relationship between B-x and B-y suggest that the spacecraft are moving with respect to an X-line and its associated Hall-structure. Yet, a simple tailward retreat of a large-scale X-line cannot account for all the observations, since several flow reversals are observed. These quasi-periodic flow reversals can also be associated with an azimuthal motion of the low frequency oscillations. Indeed, at the beginning of the interval B-y varies rapidly along the Y direction; the magnetic signature is three-dimensional and essentially corresponds to a structure of filamentary field-aligned current, moving eastward at similar to 200 km/s. The transverse size of the structure is similar to 1000 km. Similar structures are observed before and after. Thesefilamentary structures are consistent with an eastward propagation of an azimuthal modulation associated with a current system J(y), J(x). During Event 1, signatures of filamentary field-aligned current structures are also observed, in association with modulations of J(y). Hence, for both events the structure of the magnetic fields and currents is three-dimensional.

  • 10.
    Behlke, Rico
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    André, Mats
    Buchert, Stephan C.
    Vaivads, Andris
    Eriksson, Anders I.
    Lucek, Elizabeth A.
    Balogh, Andre
    Multi-point electric field measurements of Short Large-Amplitude Magnetic Structures (SLAMS) at the Earth' quasi-parallel bow shock2003In: Geophysical Research Letters, ISSN 0094-8276, Vol. 30, no 4Article in journal (Refereed)
  • 11.
    Breuillard, H.
    et al.
    CNRS, LPP, UMR, Paris, France..
    Le Contel, O.
    CNRS, LPP, UMR, Paris, France..
    Retino, A.
    CNRS, LPP, UMR, Paris, France..
    Chasapis, A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Chust, T.
    CNRS, LPP, UMR, Paris, France..
    Mirioni, L.
    CNRS, LPP, UMR, Paris, France..
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wilder, F. D.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Cohen, I.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    Royal Inst Technol, Alfven Lab, Stockholm, Sweden.
    Marklund, G. T.
    Royal Inst Technol, Alfven Lab, Stockholm, Sweden..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Goodrich, K. A.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Macri, J.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Needell, J.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Chutter, M.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Rau, D.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Dors, I.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst IWF, Graz, Austria..
    Strangeway, R. J.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Bromund, K. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst IWF, Graz, Austria..
    Fischer, D.
    Austrian Acad Sci, Space Res Inst IWF, Graz, Austria..
    Leinweber, H. K.
    Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Anderson, B. J.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Le, G.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Slavin, J. A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Kepko, E. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Baumjohann, W.
    Austrian Acad Sci, Space Res Inst IWF, Graz, Austria..
    Mauk, B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fuselier, S. A.
    Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX USA..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst IWF, Graz, Austria..
    Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 14, p. 7279-7286Article in journal (Refereed)
    Abstract [en]

    Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (approximate to 500km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.

  • 12.
    Breuillard, H.
    et al.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France.
    Matteini, L.
    UPMC Univ Paris 06, Univ Paris Diderot, PSL Res Univ, LESIA Observ Paris,CNRS, Meudon, France.
    Argall, M. R.
    Univ New Hampshire, Durham, NH 03824 USA.
    Sahraoui, F.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France.
    Andriopoulou, M.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Le Contel, O.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France.
    Retino, A.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France.
    Mirioni, L.
    Univ Paris Sud, Sorbonne Univ, Ecole Polytech, Lab Phys Plasmas,UMR7648,CNRS, Paris, France.
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Beijing, Peoples R China.
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Goodrich, K. A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Ahmadi, N.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Yordanova, Emiliya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Turner, D. L.
    Aerosp Corp, Space Sci Dept, El Segundo, CA 90245 USA.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    Chasapis, A.
    Univ Delaware, Newark, DE USA.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA.
    Torbert, R. B.
    Univ New Hampshire, Durham, NH 03824 USA.
    Russell, C. T.
    Univ Calif Los Angeles, Los Angeles, CA USA.
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Strangeway, R. J.
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Moore, T. E.
    Giles, B. L.
    Paterson, W. R.
    Pollock, C. J.
    Lavraud, B.
    Univ Paul Sabatier, CNRS UMR5277, IRAP, Toulouse, France.
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX USA.
    Cohen, I. J.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA.
    New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 859, no 2, article id 127Article in journal (Refereed)
    Abstract [en]

    The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i. e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f > 1Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves.

  • 13. Chasapis, A.
    et al.
    Retino, A.
    Sahraoui, F.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sundkvist, D.
    Greco, A.
    Sorriso-Valvo, L.
    Canu, P.
    Thin Current Sheets and Associated Electron Heating in Turbulent Space Plasma2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 804, no 1, article id L1Article in journal (Refereed)
    Abstract [en]

    Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (<3), indicating that the former are dominant for energy dissipation. Current sheets corresponding to very high PVI (>5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.

  • 14.
    Chasapis, Alexandros
    et al.
    Univ Delaware, Newark, DC USA..
    Matthaeus, W. H.
    Univ Delaware, Newark, DC USA..
    Parashar, T. N.
    Univ Delaware, Newark, DC USA..
    LeContel, O.
    Lab Phys Plasmas, Paris, France..
    Retino, A.
    Lab Phys Plasmas, Paris, France..
    Breuillard, H.
    Lab Phys Plasmas, Paris, France..
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Plantol, Toulouse, France.;Ctr Natl Rech Sci, UMR 5277, Toulouse, France..
    Eriksson, Elin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Moore, T. E.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Durham, NH 03824 USA..
    Lindqvist, P. -A
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Marklund, G.
    Royal Inst Technol, Stockholm, Sweden..
    Goodrich, K. A.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO USA..
    Chutter, M.
    Univ New Hampshire, Durham, NH 03824 USA..
    Needell, J.
    Univ New Hampshire, Durham, NH 03824 USA..
    Rau, D.
    Univ New Hampshire, Durham, NH 03824 USA..
    Dors, I.
    Univ New Hampshire, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Le, G.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Strangeway, R. J.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Bromund, K. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Leinweber, H. K.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Fischer, D.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Anderson, B. J.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Electron Heating at Kinetic Scales in Magnetosheath Turbulence2017In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 836, no 2, article id 247Article in journal (Refereed)
    Abstract [en]

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

  • 15. Chen, Li-Jen
    et al.
    Bessho, N.
    Lefebvre, B.
    Vaith, H.
    Fazakerley, A.
    Bhattacharjee, A.
    Puhl-Quinn, P. A.
    Runov, A.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Georgescu, E.
    Torbert, R.
    Evidence of an extended electron current sheet and its neighboring magnetic island during magnetotail reconnection2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A12, p. A12213-Article in journal (Refereed)
    Abstract [en]

    We have identified a spatially extended electron current sheet (ECS) and its adjacent magnetic island during a magnetotail reconnection event with no appreciable guide field. This finding is based on data from the four Cluster spacecraft and is enabled by detailed maps of electron distribution functions and DC electric fields within the diffusion region. The maps are developed using two-dimensional particle-in-cell simulations with a mass ratio m(i)/m(e) = 800. One spacecraft crossed the ECS earthward of the reconnection null and, together with the other three spacecraft, registered the following properties: (1) The ECS is colocated with a layer of bipolar electric fields normal to the ECS, pointing toward the ECS, and with a half width less than 8 electron skin depths. (2) In the inflow region up to the ECS and separatrices, electrons have a temperature anisotropy (Te-parallel to/Te-perpendicular to > 1), and the anisotropy increases toward the ECS. (3) Within about 1 ion skin depth (d(i)) above and below the ECS, the electron density decreases toward the ECS by a factor of 3-4, reaching a minimum at edges of the ECS, and has a local distinct maximum at the ECS center. (4) A di-scale magnetic island is attached to the ECS, separating it from another reconnection layer. Our simulations established that the electric field normal to the ECS is due to charge imbalance and is of the ECS scale, and ions exhibit electron-scale structures in response to this electric field.

  • 16. Chen, Li-Jen
    et al.
    Bhattacharjee, A.
    Puhl-Quinn, P. A.
    Yang, H.
    Bessho, N.
    Imada, S.
    Muehlbachler, S.
    Daly, P. W.
    Lefebvre, B.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fazakerley, A.
    Georgescu, E.
    Observation of energetic electrons within magnetic islands2008In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 4, no 1, p. 19-23Article in journal (Refereed)
    Abstract [en]

    Magnetic reconnection is the underlying process that releases impulsively an enormous amount of magnetic energy(1) in solar flares(2,3), flares on strongly magnetized neutron stars(4) and substorms in the Earth's magnetosphere(5). Studies of energy release during solar flares, in particular, indicate that up to 50% of the released energy is carried by accelerated 20-100 keV suprathermal electrons(6-8). How so many electrons can gain so much energy during reconnection has been a long-standing question. A recent theoretical study suggests that volume-filling contracting magnetic islands formed during reconnection can produce a large number of energetic electrons(9). Here we report the first evidence of the link between energetic electrons and magnetic islands during reconnection in the Earth's magnetosphere. The results indicate that energetic electron fluxes peak at sites of compressed density within islands, which imposes a new constraint on theories of electron acceleration.

  • 17. Deng, X. H.
    et al.
    Zhou, M.
    Li, S. Y.
    Baumjohann, W.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cornilleau, N.
    Santolik, O.
    Pontin, D. I.
    Reme, H.
    Lucek, E.
    Fazakerley, A. N.
    Decreau, P.
    Daly, P.
    Nakamura, R.
    Tang, R. X.
    Hu, Y. H.
    Pang, Y.
    Buechner, J.
    Zhao, H.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Pickett, J. S.
    Ng, C. S.
    Lin, X.
    Fu, S.
    Yuan, Z. G.
    Su, Z. W.
    Wang, J. F.
    Dynamics and waves near multiple magnetic null points in reconnection diffusion region2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 7, p. A07216-Article in journal (Refereed)
    Abstract [en]

    Identifying the magnetic structure in the region where the magnetic field lines break and how reconnection happens is crucial to improving our understanding of three-dimensional reconnection. Here we show the in situ observation of magnetic null structures in the diffusion region, the dynamics, and the associated waves. Possible spiral null pair has been identified near the diffusion region. There is a close relation among the null points, the bipolar signature of the Z component of the magnetic field, and enhancement of the flux of energetic electrons up to 100 keV. Near the null structures, whistler-mode waves were identified by both the polarity and the power law of the spectrum of electric and magnetic fields. It is found that the angle between the fans of the nulls is quite close to the theoretically estimated maximum value of the group-velocity cone angle for the whistler wave regime of reconnection.

  • 18.
    Divin, A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Markidis, S.
    Lapenta, G.
    Evolution of the lower hybrid drift instability at reconnection jet front2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 2675-2690Article in journal (Refereed)
    Abstract [en]

    We investigate current-driven modes developing at jet fronts during collisionless reconnection. Initial evolution of the reconnection is simulated using conventional 2-D setup starting from the Harris equilibrium. Three-dimensional PIC calculations are implemented at later stages, when fronts are fully formed. Intense currents and enhanced wave activity are generated at the fronts because of the interaction of the fast flow plasma and denser ambient current sheet plasma. The study reveals that the lower hybrid drift instability develops quickly in the 3-D simulation. The instability produces strong localized perpendicular electric fields, which are several times larger than the convective electric field at the front, in agreement with Time History of Events and Macroscale Interactions during Substorms observations. The instability generates waves, which escape the front edge and propagate into the undisturbed plasma ahead of the front. The parallel electron pressure is substantially larger in the 3-D simulation compared to that of the 2-D. In a time similar to Omega(-1)(ci), the instability forms a layer, which contains a mixture of the jet plasma and current sheet plasma. The results confirm that the lower hybrid drift instability is important for the front evolution and electron energization.

  • 19.
    Divin, Andrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lower hybrid drift instability at a dipolarization front2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 2, p. 1124-1132Article in journal (Refereed)
    Abstract [en]

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

  • 20.
    Divin, Andrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Toledo-Redondo, S.
    European Space Agcy, ESAC, Sci Directorate, Madrid, Spain..
    Markidis, S.
    KTH Royal Inst Technol, Dept Computat Sci & Technol, Stockholm, Sweden..
    Lapenta, G.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Dept Math, Leuven, Belgium..
    Three-scale structure of diffusion region in the presence of cold ions2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 12, p. 12001-12013Article in journal (Refereed)
    Abstract [en]

    Kinetic simulations and spacecraft observations typically display the two-scale structure of collisionless diffusion region (DR), with electron and ion demagnetization scales governing the spatial extent of the DR. Recent in situ observations of the nightside magnetosphere, as well as investigation of magnetic reconnection events at the Earth's magnetopause, discovered the presence of a population of cold (tens of eV) ions of ionospheric origin. We present two-dimensional particle-in-cell simulations of collisionless magnetic reconnection in multicomponent plasma with ions consisting of hot and cold populations. We show that a new cold ion diffusion region scale is introduced in between that of hot ions and electrons. Demagnetization scale of cold ion population is several times (similar to 4-8) larger than the initial cold ion gyroradius. Cold ions are accelerated and thermalized during magnetic reconnection and form ion beams moving with velocities close to the Alfven velocity.

  • 21.
    Ergun, R. E.
    et al.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA;Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Goodrich, K. A.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Ahmadi, N.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Holmes, J. C.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA;Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Eriksson, S.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Stawarz, J. E.
    Imperial Coll London, Blackett Lab, London, England.
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Hesse, M.
    Univ Bergen, Dept Phys & Technol, Bergen, Norway.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA.
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX USA;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.
    Schwartz, S. J.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Eastwood, J. P.
    Imperial Coll London, Blackett Lab, London, England.
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA.
    Le Contel, O.
    Univ Paris Sud, Observ Paris, Sorbonne Univ, Lab Phys Plasmas,CNRS,Ecole Polytech, Paris, France.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA.
    Argall, M. R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.
    Lindqvist, P. -A
    Chen, L. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA;Univ Maryland, Dept Astron, College Pk, MD 20742 USA.
    Cassak, P. A.
    West Univ Virginia, Dept Phys & Astron, Morgantown, WV USA.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Gershman, D.
    West Univ Virginia, Dept Phys & Astron, Morgantown, WV USA.
    Leonard, T. W.
    Univ Colorado, Lab Atmospher & Space Sci, Boulder, CO 80309 USA.
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, Toulouse, France;CNRS, Toulouse, France.
    Retino, A.
    Univ Paris Sud, Observ Paris, Sorbonne Univ, Lab Phys Plasmas,CNRS,Ecole Polytech, Paris, France.
    Matthaeus, W.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 8, p. 3338-3347Article in journal (Refereed)
    Abstract [en]

    We report observations of turbulent dissipation and particle acceleration from large-amplitude electric fields (E) associated with strong magnetic field (B) fluctuations in the Earth's plasma sheet. The turbulence occurs in a region of depleted density with anti-earthward flows followed by earthward flows suggesting ongoing magnetic reconnection. In the turbulent region, ions and electrons have a significant increase in energy, occasionally > 100 keV, and strong variation. There are numerous occurrences of vertical bar E vertical bar > 100 mV/m including occurrences of large potentials (> 1 kV) parallel to B and occurrences with extraordinarily large J.E (J is current density). In this event, we find that the perpendicular contribution of J.E with frequencies near or below the ion cyclotron frequency (f(ci)) provide the majority net positive J.E. Large-amplitude parallel E events with frequencies above f(ci) to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration. Plain Language Summary The Magnetospheric Multiscale mission is able to examine dissipation associated with magnetic reconnection with unprecedented accuracy and frequency response. The observations show that roughly 80% of the dissipation is from the perpendicular currents and electric fields. However, large-amplitude parallel electric fields appear to play a strong role in turbulent dissipation into electrons and in electron acceleration.

  • 22.
    Eriksson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Graham, Daniel B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Divin, Andrey
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Physics Department, St. Petersburg State University, St. Petersburg, Russia.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Yordanova, Emiliya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Electron Energization at a Reconnecting Magnetosheath Current Sheet2018In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 16Article in journal (Refereed)
    Abstract [en]

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

  • 23.
    Eriksson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Graham, Daniel. B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Yordanova, Emiliya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hietala, H.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Avanov, L. A.
    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.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lavraud, B.
    CNRS, IRAP, Toulouse, France..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Saito, Y.
    JAXA, Chofu, Tokyo, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C.
    Torbert, R.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Ergun, R.
    Univ Colorado, Atmospher & Space Phys Lab, Boulder, CO 80309 USA..
    Lindqvist, P-A
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Strong current sheet at a magnetosheath jet: Kinetic structure and electron acceleration2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 10, p. 9608-9618Article in journal (Refereed)
    Abstract [en]

    Localized kinetic-scale regions of strong current are believed to play an important role in plasma thermalization and particle acceleration in turbulent plasmas. We present a detailed study of a strong localized current, 4900 nA m(-2), located at a fast plasma jet observed in the magnetosheath downstream of a quasi-parallel shock. The thickness of the current region is similar to 3 ion inertial lengths and forms at a boundary separating magnetosheath-like and solar wind-like plasmas. On ion scales the current region has the shape of a sheet with a significant average normal magnetic field component but shows strong variations on smaller scales. The dynamic pressure within the magnetosheath jet is over 3 times the solar wind dynamic pressure. We suggest that the current sheet is forming due to high velocity shears associated with the jet. Inside the current sheet we observe local electron acceleration, producing electron beams, along the magnetic field. However, there is no clear sign of ongoing reconnection. At higher energies, above the beam energy, we observe a loss cone consistent with part of the hot magnetosheath-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within the current sheet is similar to the one that occurs at shocks, where electron beams and loss cones are also observed. Therefore, electron beams observed in the magnetosheath do not have to originate from the bow shock but can also be generated locally inside the magnetosheath.

  • 24.
    Eriksson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyayintsev, V. M.
    Taras Shevchenko Natl Univ Kyiv, Dept Theoret Phys, Kiev, Ukraine..
    Andre, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Statistics and accuracy of magnetic null identification in multispacecraft data2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, p. 6883-6889Article in journal (Refereed)
    Abstract [en]

    Complex magnetic topologies are ubiquitous in astrophysical plasmas. Analyzing magnetic nulls, regions of vanishing magnetic field, is one way to characterize 3-D magnetic topologies. Magnetic nulls are believed to be important in 3-D reconnection and turbulence. In the vicinity of a null, plasma particles become unmagnetized and can be accelerated to high energies by electric fields. We present the first statistical study of the occurrence of magnetic nulls and their types in the Earth's nightside magnetosphere. We are able to identify the nulls both in the tail and in the magnetopause current sheets. On average, we find one null for every few current sheet crossings. We show that the type identification of magnetic nulls may be sensitive to local fluctuations in the magnetic field. We develop and demonstrate a method to estimate the reliability of the magnetic null type identification.

  • 25. Farrugia, C. J.
    et al.
    Chen, Li-Jen
    Torbert, R. B.
    Southwood, D. J.
    Cowley, S. W. H.
    Vrublevskis, A.
    Mouikis, C.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Decreau, P.
    Vaith, H.
    Owen, C. J.
    Sibeck, D. J.
    Lucek, E.
    Smith, C. W.
    "Crater" flux transfer events: Highroad to the X line?2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no 2, p. A02204-Article in journal (Refereed)
    Abstract [en]

    We examine Cluster observations of a so-called magnetosphere "crater FTE," employing data from five instruments (FGM, CIS, EDI, EFW, and WHISPER), some at the highest resolution. The aim of doing this is to deepen our understanding of the reconnection nature of these events by applying recent advances in the theory of collisionless reconnection and in detailed observational work. Our data support the hypothesis of a stratified structure with regions which we show to be spatial structures. We support the bulge-like topology of the core region (R3) made up of plasma jetting transverse to reconnected field lines. We document encounters with a magnetic separatrix as a thin layer embedded in the region (R2) just outside the bulge, where the speed of the protons flowing approximately parallel to the field maximizes: (1) short (fraction of a sec) bursts of enhanced electric field strengths (up to similar to 30 mV/m) and (2) electrons flowing against the field toward the X line at approximately the same time as the bursts of intense electric fields. R2 also contains a density decrease concomitant with an enhanced magnetic field strength. At its interface with the core region, R3, electric field activity ceases abruptly. The accelerated plasma flow profile has a catenary shape consisting of beams parallel to the field in R2 close to the R2/R3 boundary and slower jets moving across the magnetic field within the bulge region. We detail commonalities our observations of crater FTEs have with reconnection structures in other scenarios. We suggest that in view of these properties and their frequency of occurrence, crater FTEs are ideal places to study processes at the separatrices, key regions in magnetic reconnection. This is a good preparation for the MMS mission.

  • 26. Fu, H. S.
    et al.
    Cao, J. B.
    Cully, C. M.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Angelopoulos, V.
    Zong, Q. -G
    Santolik, O.
    Macusova, E.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Liu, W. L.
    Lu, H. Y.
    Zhou, M.
    Huang, S. Y.
    Zhima, Z.
    Whistler-mode waves inside flux pileup region: Structured or unstructured?2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 11, p. 9089-9100Article in journal (Refereed)
    Abstract [en]

    During reconnection, a flux pileup region (FPR) is formed behind a dipolarization front in an outflow jet. Inside the FPR, the magnetic field magnitude and Bz component increase and the whistler-mode waves are observed frequently. As the FPR convects toward the Earth during substorms, it is obstructed by the dipolar geomagnetic field to form a near-Earth FPR. Unlike the structureless emissions inside the tail FPR, we find that the whistler-mode waves inside the near-Earth FPR can exhibit a discrete structure similar to chorus. Both upper band and lower band chorus are observed, with the upper band having a larger propagation angle (and smaller wave amplitude) than the lower band. Most chorus elements we observed are rising-tone type, but some are falling-tone type. We notice that the rising-tone chorus can evolve into falling-tone chorus within <3s. One of the factors that may explain why the waves are unstructured inside the tail FPR but become discrete inside the near-Earth FPR is the spatial inhomogeneity of magnetic field: we find that such inhomogeneity is small inside the near-Earth FPR but large inside the tail FPR.

  • 27.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dunlop, M.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Liu, W. L.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Lu, H. Y.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Wuhan 430072, Peoples R China..
    Ma, Y. D.
    Beihang Univ, Sch Space & Environm, Beijing 100191, Peoples R China..
    Eriksson, Elin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Identifying magnetic reconnection events using the FOTE method2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 2, p. 1263-1272Article in journal (Refereed)
    Abstract [en]

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

  • 28.
    Fu, H. S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Y. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sergeev, V. A.
    Huang, S. Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Kronberg, E. A.
    Daly, P. W.
    Pitch angle distribution of suprathermal electrons behind dipolarization fronts: A statistical overview2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. A12221-Article in journal (Refereed)
    Abstract [en]

    We examine the pitch angle distribution (PAD) of suprathermal electrons (> 40 keV) inside the flux pileup regions (FPRs) that are located behind the dipolarization fronts (DFs), in order to better understand the particle energization mechanisms operating therein. The 303 earthward-propagating DFs observed during 9 years (2001-2009) by Cluster 1 have been analyzed and divided into two groups according to the differential fluxes of the > 40 keV electrons inside the FPR. One group, characterized by the low flux (F < 500/cm(2) , s . sr . keV), consists of 153 events and corresponds to a broad distribution of IMF Bz components. The other group, characterized by the high flux (F >= 500/cm(2) . s . sr . keV), consists of 150 events and corresponds to southward IMF Bz components. Only the high-flux group is considered to investigate the PAD of the > 40 keV electrons as the low-flux situation may lead to large uncertainties in computing the anisotropy factor that is defined as A = F-perpendicular to/F-parallel to - 1 for F-perpendicular to > F-parallel to, and A = -F-parallel to/F-perpendicular to + 1 for F-perpendicular to < F-parallel to. We find that, among the 150 events, 46 events have isotropic distribution (vertical bar A vertical bar <= 0.5); 60 events have perpendicular distribution (A > 0.5), and 44 events have field-aligned distribution inside the FPR (A < -0.5). The perpendicular distribution appears mainly inside the growing FPR, where the flow velocity is increasing and the local flux tube is compressed. The field-aligned distribution occurs mainly inside the decaying FPR, where the flow velocity is decreasing and the local flux tube is expanding. Inside the steady FPR, we observed primarily the isotropic distribution of suprathermal electrons. This statistical result confirms the previous case study and gives an overview of the PAD of suprathermal electrons behind DFs.

  • 29.
    Fu, H. S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Retino, A.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Energetic electron acceleration by unsteady magnetic reconnection2013In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 9, no 7, p. 426-430Article in journal (Refereed)
    Abstract [en]

    The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares(1,2),substorms(34), and disruptions in fusion experiments(5,6).Observations in the solar chromosphere(1) and the Earth's magnetosphere(7-10) indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent(11). Here we show that energetic electron acceleration is caused by unsteady reconnection. In the Earth's magnetosphere and the solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady(12), so energetic electrons are absent(11). The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain for the peak observed fluxes.

  • 30.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Olshevsky, V.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Leuven, Belgium..
    Eastwood, J. P.
    Imperial Coll London, Blackett Lab, London, England..
    Retino, A.
    UPMC, Ecole Polytech, CNRS, Lab Phys Plasmas, Palaiseau, France..
    Intermittent energy dissipation by turbulent reconnection2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 1, p. 37-43Article in journal (Refereed)
    Abstract [en]

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

  • 31.
    Fu, H. S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Beihang Univ, Space Sci Inst, Sch Astronaut, Beijing 100191, Peoples R China.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Olshevsky, V.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Dept Math, Leuven, Belgium.;Main Astron Observ NAS, Kiev, Ukraine..
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Cao, J. B.
    Beihang Univ, Space Sci Inst, Sch Astronaut, Beijing 100191, Peoples R China..
    Huang, S. Y.
    Ecole Polytech, CNRS, UPMC, Lab Phys Plasmas, F-91128 Palaiseau, France.;Wuhan Univ, Sch Elect & Informat, Wuhan 430072, Peoples R China.
    Retino, A.
    Ecole Polytech, CNRS, UPMC, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Lapenta, G.
    Katholieke Univ Leuven, Ctr Math Plasma Astrophys, Dept Math, Leuven, Belgium..
    How to find magnetic nulls and reconstruct field topology with MMS data?2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 5, p. 3758-3782Article in journal (Refereed)
    Abstract [en]

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

  • 32.
    Fu, Huishan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Huang, S. Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Occurrence rate of earthward-propagating dipolarization fronts2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, p. L10101-Article in journal (Refereed)
    Abstract [en]

    The occurrence rate of earthward-propagating dipolarization fronts (DFs) is investigated in this paper based on the 9 years (2001-2009) of Cluster 1 data. For the first time, we select the DF events by fitting the characteristic increase in B-z using a hyperbolic tangent function. 303 earthward-propagating DFs are found; they have on average a duration of 4 s and a B-z increase of 8 nT. DFs have the maximum occurrence at Z(GSM) approximate to 0 and r approximate to 15 R-E with one event occurring every 3.9 hours, where r is the distance to the center of the Earth in the XYGSM plane. The maximum occurrence rate at Z(GSM) approximate to 0 can be explained by the steep and large increase of B-z near the central current sheet, which is consistent with previous simulations. Along the r direction, the occurrence rate increases gradually from r approximate to 20 to r approximate to 15 R-E but decreases rapidly from r approximate to 15 to r approximate to 10 R-E. This may be due to the increasing pileup of the magnetic flux from r approximate to 20 to r approximate to 15 R-E and the strong background magnetic field at r <similar to 13 R-E, where the magnetic field changes from the tail-like to dipolar shape. The maximum occurrence rate of DFs (one event per 3.9 hours) is comparable to that of substorms, indicating a relation between the two.

  • 33.
    Fu, Huishan S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L16104-Article in journal (Refereed)
    Abstract [en]

    Two dipolarization front (DF) structures observed by Cluster in the Earth midtail region (X(GSM) approximate to -15 R(E)), showing respectively the feature of Fermi and betatron acceleration of suprathermal electrons, are studied in detail in this paper. Our results show that Fermi acceleration dominates inside a decaying flux pileup region (FPR), while betatron acceleration dominates inside a growing FPR. Both decaying and growing FPRs are associated with the DF and can be distinguished by examining whether the peak of the bursty bulk flow (BBF) is co-located with the DF (decaying) or is behind the DF (growing). Fermi acceleration is routinely caused by the shrinking length of flux tubes, while betatron acceleration is caused by a local compression of the magnetic field. With a simple model, we reproduce the processes of Fermi and betatron acceleration for the higher-energy (>40 keV) electrons. For the lower-energy (<20 keV) electrons, Fermi and betatron acceleration are not the dominant processes. Our observations reveal that betatron acceleration can be prominent in the midtail region even though the magnetic field lines are significantly stretched there.

  • 34.
    Fu, Huishan S.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Huang, S. Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Electric structure of dipolarization front at sub-proton scale2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, p. L06105-Article in journal (Refereed)
    Abstract [en]

    Using Cluster data, we investigate the electric structure of a dipolarization front (DF) - the ion inertial length (c/omega(pi)) scale boundary in the Earth's magnetotail formed at the front edge of an earthward propagating flow with reconnected magnetic flux. We estimate the current density and the electron pressure gradient throughout the DF by both single-spacecraft and multi-spacecraft methods. Comparison of the results from the two methods shows that the single-spacecraft analysis, which is capable of resolving the detailed structure of the boundary, can be applied for the DF we study. Based on this, we use the current density and the electron pressure gradient from the single-spacecraft method to investigate which terms in the generalized Ohm's law balance the electric field throughout the DF. We find that there is an electric field at ion inertia scale directed normal to the DF; it has a duskward component at the dusk flank of DF but a dawnward component at the dawn flank of DF. This electric field is balanced by the Hall (j x B/ne) and electron pressure gradient (del P-e/ne) terms at the DF, with the Hall term being dominant. Outside the narrow DF region, however, the electric field is balanced by the convection (V-i x B) term, meaning the frozen-in condition for ions is broken only at the DF itself. In the reference frame moving with the DF the tangential electric field is almost zero, indicating there is no flow of plasma across the DF and that the DF is a tangential discontinuity. The normal electric field at the DF constitutes a potential drop of similar to 1 keV, which may reflect and accelerate the surrounding ions. 

  • 35. Gedalin, M.
    et al.
    Medvedev, M.
    Spitkovsky, A.
    Krasnoselskikh, V.
    Balikhin, M.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Perri, S.
    Growth of filaments and saturation of the filamentation instability2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 3, p. 032108-Article in journal (Refereed)
    Abstract [en]

    The filamentation instability of counterstreaming beams is a nonresonant hydrodynamic-type instability whose growth rate is a smooth function of the wavelength (scale). As a result, perturbations with all unstable wavelengths develop, and the growth saturates due to the saturation of available current. For a given scale, the magnetic field at saturation is proportional to the scale. As a result, the instability develops in a nearly linear regime, where the unstable modes stop growing as soon as the saturation of the corresponding wavelength is reached. At each moment there exists a dominant scale of the magnetic field which is the scale that reached saturation at this particular time. The smaller scales do not disappear and can be easily distinguished in the current structure. The overall growth of the instability stops when the loss of the streaming ion energy because of deceleration is comparable to the initial ion energy.

  • 36. Gedalin, M.
    et al.
    Spitkovsky, A.
    Medvedev, M.
    Balikhin, M.
    Krasnoselskikh, V.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Perri, S.
    Relativistic filamentary equilibria2011In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 77, p. 193-205Article in journal (Refereed)
    Abstract [en]

    Plasma filamentation is often encountered in collisionless shocks and inertial confinement fusion. We develop a general analytical description of the two-dimensional relativistic filamentary equilibrium and derive the conditions for existence of potential-free equilibria. A pseudopotential equation for the vector-potential is constructed for cold and relativistic Maxwellian distributions. The role of counter-streaming is explained. We present single current sheet and periodic current sheet solutions, and analyze the equilibria with electric potential. These solutions can be used to study linear and nonlinear evolution of the relativistic filamentation instability.

  • 37.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Swedish Inst Space Phys, Uppsala, Sweden..
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Norgren, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    Marklund, G. T.
    KTH Royal Inst Technol, Sch Elect Engn, Space & Plasma Phys, Stockholm, Sweden..
    Ergun, R. E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Planetol, Toulouse, France.;CNRS, Toulouse, France..
    Saito, Y.
    JAXA, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria..
    Russell, C. T.
    Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria.;Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Strangeway, R. J.
    Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria.;Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Burch, J. L.
    SW Res Inst, San Antonio, TX USA..
    Electron currents and heating in the ion diffusion region of asymmetric reconnection2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 10, p. 4691-4700Article in journal (Refereed)
    Abstract [en]

    In this letter the structure of the ion diffusion region of magnetic reconnection at Earth's magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.

  • 38.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Norgren, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Toledo-Redondo, S.
    European Space Agcy ESAC, Madrid, Spain..
    Lindqvist, P. -A
    Marklund, G. T.
    KTH Royal Inst Technol, Sch Elect Engn, Space & Plasma Phys, Stockholm, Sweden..
    Ergun, R. E.
    Univ Colorado Boulder, Lab Atmospher & Space Phys, Boulder, CO USA..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, C. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Avanov, L. A.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, Dept Astron, College Pk, MD USA..
    Lavraud, B.
    Univ Toulouse UPS, Inst Rech Astrophys & Plantol, Toulouse, France.;Ctr Natl Rech Sci, Toulouse, France..
    Saito, Y.
    JAXA, Inst Space & Aeronaut Sci, Sagamihara, Kanagawa, Japan..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Lower hybrid waves in the ion diffusion and magnetospheric inflow regions2017In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 1, p. 517-533Article in journal (Refereed)
    Abstract [en]

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

  • 39.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Electrostatic solitary waves and electrostatic waves at the magnetopause2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 4, p. 3069-3092Article in journal (Refereed)
    Abstract [en]

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

  • 40.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Electrostatic solitary waves with distinct speeds associated with asymmetric reconnection2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 2, p. 215-224Article in journal (Refereed)
    Abstract [en]

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

  • 41.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fazakerley, A. N.
    Electron Dynamics in the Diffusion Region of an Asymmetric Magnetic Reconnection2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 21, p. 215004-Article in journal (Refereed)
    Abstract [en]

    During a magnetopause crossing near the subsolar point Cluster observes the ion diffusion region of antiparallel magnetic reconnection. The reconnecting plasmas are asymmetric, differing in magnetic field strength, density, and temperature. Spatial changes in the electron distributions in the diffusion region are resolved and investigated in detail. Heating of magnetosheath electrons parallel to the magnetic field is observed. This heating is shown to be consistent with trapping of magnetosheath electrons by parallel electric fields.

  • 42.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Norgren, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Space Plasma Physics.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX 77005 USA.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX 78238 USA.
    Lindqvist, P. -A
    Space and Plasma Physics, School of Electrical Engineering, KTH Royal Institute of Technology, Stockholm SE-11428, Sweden.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA.
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Gershman, D. J.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA;NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90095 USA.
    Instability of Agyrotropic Electron Beams near the Electron Diffusion Region2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 2, article id 025101Article in journal (Refereed)
    Abstract [en]

    During a magnetopause crossing the Magnetospheric Multiscale spacecraft encountered an electron diffusion region (EDR) of asymmetric reconnection. The EDR is characterized by agyrotropic beam and crescent electron distributions perpendicular to the magnetic field. Intense upper-hybrid (UH) waves are found at the boundary between the EDR and magnetosheath inflow region. The UH waves are generated by the agyrotropic electron beams. The UH waves are sufficiently large to contribute to electron diffusion and scattering, and are a potential source of radio emission near the EDR. These results provide observational evidence of wave-particle interactions at an EDR, and suggest that waves play an important role in determining the electron dynamics.

  • 43.
    Graham, Daniel B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, Observ Paris, LPP,UMR7648,CNRS,Ecole Polytech, Paris, France.
    Malaspina, D. M.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Lindqvist, P. -A
    Wilder, F. D.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Gershman, D. J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA;Univ Maryland, Dept Astron, College Pk, MD 20742 USA.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA.
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA.
    Large-Amplitude High-Frequency Waves at Earth's Magnetopause2018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 4, p. 2630-2657Article in journal (Refereed)
    Abstract [en]

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

  • 44.
    Hamrin, M.
    et al.
    Umea Univ, Dept Phys, Umea, Sweden..
    Andersson, L.
    LASP, Boulder, CO USA..
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Pitkanen, T.
    Umea Univ, Dept Phys, Umea, Sweden..
    Gunell, H.
    Belgian Inst Space Aeron, Brussels, Belgium..
    The use of the power density for identifying reconnection regions2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 10, p. 8644-8662Article in journal (Refereed)
    Abstract [en]

    In the vicinity of magnetic reconnection, magnetic energy is transferred into kinetic energy. A reconnection region hence corresponds to a load, and it should manifest itself as large and positive values of the power density, E<bold>J </bold>>> 0, where E is the electric field and J the current density. In this article we analyze Cluster plasma sheet data from 2001-2004 to investigate the use of the power density for identifying possible magnetic reconnection events from large sets of observed data. From theoretical arguments we show that an event with E<bold>J</bold>20pW/m(3) in the Earth's magnetotail observed by the Cluster instruments (X <- 10R(E) and |Y|less than or similar to 10RE) is likely to be associated with reconnection. The power density can be used as a primary indicator of potential reconnection regions, but selected events must be reviewed separately to confirm any possible reconnection signatures by looking for other signatures such as Hall electric and magnetic fields and reconnection jets. The power density can be computed from multispacecraft data, and we argue that the power density can be used as a tool for identifying possible reconnection events from large sets of data, e.g., from the Cluster and the Magnetospheric Multiscale missions.

  • 45. Hamrin, M.
    et al.
    Norqvist, P.
    Marghitu, O.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Klecker, B.
    Kistler, L. M.
    Dandouras, I.
    Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet2009In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, no 11, p. 4147-4155Article in journal (Refereed)
    Abstract [en]

    In this article, and in a companion paper by Hamrin et al. (2009) [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs) in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data) at the altitude of about 15-20 R-E in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs) and 35 Concentrated Generator Regions (CGRs). By examining variations in the power density, E.J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 R-E less than or similar to Delta 1 S-ECR less than or similar to 5 R-E. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1-10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005). The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1-10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

  • 46. Hamrin, M.
    et al.
    Pitkanen, T.
    Norqvist, P.
    Karlsson, T.
    Nilsson, H.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Buchert, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Marghitu, O.
    Klecker, B.
    Kistler, L. M.
    Dandouras, I.
    Evidence for the braking of flow bursts as they propagate toward the Earth2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 11, p. 9004-9018Article in journal (Refereed)
    Abstract [en]

    In this article we use energy conversion arguments to investigate the possible braking of flow bursts as they propagate toward the Earth. By using EJ data (E and J are the electric field and the current density) observed by Cluster in the magnetotail plasma sheet, we find indications of a plasma deceleration in the region -20 R-E < X < - 15 R-E. Our results suggest a braking mechanism where compressed magnetic flux tubes in so-called dipolarization fronts (DFs) can decelerate incoming flow bursts. Our results also show that energy conversion arguments can be used for studying flow braking and that the position of the flow velocity peak with respect to the DF can be used as a single-spacecraft proxy when determining energy conversion properties. Such a single-spacecraft proxy is invaluable whenever multispacecraft data are not available. In a superposed epoch study, we find that a flow burst with the velocity peak behind the DF is likely to decelerate and transfer energy from the particles to the fields. For flow bursts with the peak flow at or ahead of the DF we see no indications of braking, but instead we find an energy transfer from the fields to the particles. From our results we obtain an estimate of the magnitude of the deceleration of the flow bursts, and we find that it is consistent with previous investigations.

  • 47. Hamrin, M.
    et al.
    Rönnmark, K.
    Borlin, N.
    Vedin, J.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    GALS - Gradient Analysis by Least Squares2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 11, p. 3491-3499Article in journal (Refereed)
    Abstract [en]

    We present a method, GALS (Gradient Analysis by Least Squares) for estimating the gradient of a physical field from multi-spacecraft observations. To obtain the best possible spatial resolution, the gradient is estimated in the frame of reference where structures in the field are essentially locally stationary. The estimates are refined iteratively by a least squares method. We show that GALS is not very sensitive to the spacecraft configuration and resolves structures much smaller than the characteristic size of the spacecraft distribution. Furthermore, GALS requires little user input. GALS has been tested on synthetic magnetic field data and data from the Cluster FGM instrument. GALS will also be useful for other types of data. The results indicate that GALS is robust and superior to the curlometer method for estimating the current from magnetic field measurements.

  • 48. Hasegawa, H.
    et al.
    Retino, A.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nakamura, T. K. M.
    Teh, W. -L
    Sonnerup, B. U. Oe.
    Schwartz, S. J.
    Seki, Y.
    Fujimoto, M.
    Saito, Y.
    Reme, H.
    Canu, P.
    Kelvin-Helmholtz waves at the Earth's magnetopause: Multiscale development and associated reconnection2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 12, p. A12207-Article in journal (Refereed)
    Abstract [en]

    We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at similar to 1500 magnetic local time (MLT) by the Geotail spacecraft and at similar to 1900 MLT by the Cluster spacecraft, which detected rolled-up MHD-scale vortices generated by the Kelvin-Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD-scale and ion-scale structures of the vortices, and the formation mechanism of the low-latitude boundary layer (LLBL). The observed KH wavelength (>4 x 10(4) km) is considerably longer than predicted by the linear theory from the thickness (similar to 1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high-latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length similar to 100 km and of magnetic shear similar to 60 degrees existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvenic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field-aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk-flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.

  • 49. Hasegawa, H.
    et al.
    Retino, A.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Nakamura, R.
    Takada, T.
    Miyashita, Y.
    Reme, H.
    Lucek, E. A.
    Retreat and reformation of X-line during quasi-continuous tailward-of-the-cusp reconnection under northward IMF2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no 15, p. L15104-Article in journal (Refereed)
    Abstract [en]

    We present observations on 19-20 November 2006 by the Cluster spacecraft that were skimming the high-latitude dusk-flank magnetopause, which are consistent with more than one reconnection X-line present on the tailward side of the cusp under northward IMF. Evidence of quasi-continuous reconnection over 16 hours exists in the form of Alfvenic acceleration of magnetosheath ions found almost always when either of the satellites traversed the boundary. The data indicate that a dominant X-line was sunward of Cluster for most of the time, but ion velocity distributions consisting of two magnetosheath populations demonstrate that for part of the time, more than one X-line existed. Further, the motion of reconnected field lines shows that some X-line(s) retreated tailward. It is inferred that following the X-line retreat, another X-line reformed sunward of Cluster, leading tomultiple X-lines.

  • 50. Hietala, H.
    et al.
    Laitinen, Tiera V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andreeova, K.
    Vainio, R.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Palmroth, M.
    Pulkkinen, T. I.
    Koskinen, H. E. J.
    Lucek, E. A.
    Reme, H.
    Supermagnetosonic Jets behind a Collisionless Quasiparallel Shock2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 24, p. 245001-Article in journal (Refereed)
    Abstract [en]

    The downstream region of a collisionless quasiparallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multispacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasiparallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasiparallel shocks in many plasma environments.

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