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  • 1. Alm, L.
    et al.
    André, M.
    Vaivads, Andris
    Khotyaintsev, Y. V.
    Torbert, R. B.
    Burch, J. L.
    Ergun, R. E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, C. T.
    Giles, B. L.
    Mauk, B. H.
    Magnetotail Hall Physics in the Presence of Cold Ions2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 20, s. 10,941-10,950Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the first in situ observation of cold ionospheric ions modifying the Hall physics of magnetotail reconnection. While in the tail lobe, Magnetospheric Multiscale mission observed cold (tens of eV) E × B drifting ions. As Magnetospheric Multiscale mission crossed the separatrix of a reconnection exhaust, both cold lobe ions and hot (keV) ions were observed. During the closest approach of the neutral sheet, the cold ions accounted for ∼30% of the total ion density. Approximately 65% of the initial cold ions remained cold enough to stay magnetized. The Hall electric field was mainly supported by the j × B term of the generalized Ohm's law, with significant contributions from the ∇·P e and v c ×B terms. The results show that cold ions can play an important role in modifying the Hall physics of magnetic reconnection even well inside the plasma sheet. This indicates that modeling magnetic reconnection may benefit from including multiscale Hall physics.

  • 2.
    Alm, Love
    et al.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Andre, Mats
    Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, Daniel B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Khotvaintsev, Yuri, V
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, Andris
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Chappell, Charles R.
    Vanderbilt Univ, Dept Phys & Astron, Vanderbilt Dyer Observ, Nashville, TN 37235 USA..
    Dargent, Jeremy
    Univ Pisa, Phys Dept Enrico Fermi, Pisa, Italy..
    Fuselier, Stephen A.
    Southwest Res Inst, San Antonio, TX USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX USA..
    Haaland, Stein
    Max Planck Inst Solar Syst Res, Gottingen, Germany.;Univ Bergen, Birkeland Ctr Space Sci, Bergen, Norway..
    Lavraud, Benoit
    Univ Toulouse, Inst Rech Astrophys & Planetol, CNRS, UPS,CNES, Toulouse, France..
    Li, Wenya
    Chinese Acad Sci, Natl Space Sci Ctr, State Key Lab Space Weather, Beijing, Peoples R China..
    Tenfjord, Paul
    Univ Bergen, Birkeland Ctr Space Sci, Bergen, Norway..
    Toledo-Redondo, Sergio
    Univ Toulouse, Inst Rech Astrophys & Planetol, CNRS, UPS,CNES, Toulouse, France..
    Vines, Sarah K.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    MMS Observations of Multiscale Hall Physics in the Magnetotail2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present Magnetospheric Multiscale mission (MMS) observations of Hall physics in the magnetotail, which compared to dayside Hall physics is a relatively unexplored topic. The plasma consists of electrons, moderately cold ions (T similar to 1.5 keV) and hot ions (T similar to 20 keV). MMS can differentiate between the cold ion demagnetization region and hot ion demagnetization regions, which suggests that MMS was observing multiscale Hall physics. The observed Hall electric field is compared with a generalized Ohm's law, accounting for multiple ion populations. The cold ion population, despite its relatively high initial temperature, has a significant impact on the Hall electric field. These results show that multiscale Hall physics is relevant over a much larger temperature range than previously observed and is relevant for the whole magnetosphere as well as for other astrophysical plasma.

  • 3. Andre, M.
    et al.
    Li, W.
    Toledo-Redondo, S.
    Khotyaintsev, Yu. V.
    Vaivads, Andris
    Graham, D. B.
    Norgren, C.
    Burch, J.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R.
    Torbert, R.
    Magnes, W.
    Russell, C. T.
    Giles, B.
    Moore, T. E.
    Chandler, M. O.
    Pollock, C.
    Young, D. T.
    Avanov, L. A.
    Dorelli, J. C.
    Gershman, D. J.
    Paterson, W. R.
    Lavraud, B.
    Saito, Y.
    Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 13, s. 6705-6712Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

  • 4. Andriopoulou, M.
    et al.
    Nakamura, R.
    Torkar, K.
    Baumjohann, W.
    Torbert, R. B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Khotyaintsev, Y. V.
    Dorelli, J.
    Burch, J. L.
    Russell, C. T.
    Study of the spacecraft potential under active control and plasma density estimates during the MMS commissioning phase2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4858-4864Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Each spacecraft of the recently launched magnetospheric multiscale MMS mission is equipped with Active Spacecraft Potential Control (ASPOC) instruments, which control the spacecraft potential in order to reduce spacecraft charging effects. ASPOC typically reduces the spacecraft potential to a few volts. On several occasions during the commissioning phase of the mission, the ASPOC instruments were operating only on one spacecraft at a time. Taking advantage of such intervals, we derive photoelectron curves and also perform reconstructions of the uncontrolled spacecraft potential for the spacecraft with active control and estimate the electron plasma density during those periods. We also establish the criteria under which our methods can be applied.

  • 5.
    André, Mats
    et al.
    Uppsala universitet, Institutionen för astronomi och rymdfysik.
    Vaivads, Andris
    Buchert, Stephan C.
    Fazakerley, A. N.
    Lahiff, A.
    Thin electron-scale layers at the magnetopause2004Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 31, s. L03803-Artikkel i tidsskrift (Fagfellevurdert)
  • 6.
    André, Mats
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yu V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Laitinen, Tiera V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Nilsson, H.
    Stenberg, G.
    Fazakerley, A.
    Trotignon, J. G.
    Magnetic reconnection and cold plasma at the magnetopause2010Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, nr 22, s. L22108-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 7.
    Artemyev, A. V.
    et al.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.;Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA.;RAS, Space Res Inst, Moscow, Russia..
    Pritchett, P. L.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90024 USA..
    Angelopoulos, V.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.;Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Zhang, X. -J
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Lu, S.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.;Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Runov, A.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.;Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Fuselier, S. A.
    Southwest Res Inst, San Antonio, TX USA..
    Wellenzohn, S.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.;Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA.;Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90024 USA..
    Lindqvist, Per-Arne
    KTH.
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Field-Aligned Currents Originating From the Magnetic Reconnection Region: Conjugate MMS-ARTEMIS Observations2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 12, s. 5836-5844Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Near-Earth magnetic reconnection reconfigures the magnetotail and produces strong plasma flows that transport plasma sheet particles and electromagnetic energy to the inner magnetosphere. An essential element of such a reconfiguration is strong, transient field-aligned currents. These currents, believed to be generated within the plasma sheet and closed at the ionosphere, are responsible for magnetosphere-ionosphere coupling during substorms. We use conjugate measurements from Magnetospheric Multiscale (MMS) at the plasma sheet boundary (around x approximate to- 10R(E)) and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) at the equator (around x approximate to- 60R(E)) to explore the potential generation region of these currents. We find a clear correlation between the field-aligned current intensity measured by MMS and the tailward plasma sheet flows measured by ARTEMIS. To better understand the origin of this correlation, we compare spacecraft observations with results from 3-D particle-in-cell simulations of magnetotail reconnection. The comparison reveals that field-aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between MMS (near-Earth) and ARTEMIS (at lunar distance). A weak correlation between the field-aligned current intensity at MMS and earthward flow magnitudes at ARTEMIS suggests that distant magnetotail reconnection does not significantly contribute to the generation of the observed near-Earth currents. Our findings support the idea that the dominant role of the near-Earth magnetotail reconnection in the field-aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long-term field-aligned current system. Plain Language Summary Field-aligned currents connect the Earth magnetotail and ionosphere, proving energy and information transport from the region where main energy release process, magnetic reconnection, occurs to the region where the collisional energy dissipation takes place. Therefore, investigation and modeling of the field-aligned current generation is important problem of the magnetosphere plasma physics. However, field-aligned current investigation requires simultaneous observations of reconnection signatures in the magnetotail and at high latitudes. Simultaneous and conjugate operation of two multispacecraft missions, Magnetospheric Multiscale and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun, for the first time provide an opportunity for such investigation. Combining spacecraft observations with results from 3-D particle-in-cell simulations of magnetotail reconnection, we demonstrate that field-aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between near-Earth (Magnetospheric Multiscale location) and lunar distant tail (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun location). Our findings support the idea that the dominant role of the near-Earth magnetotail reconnection in the field-aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long-term field-aligned current system.

  • 8.
    Backrud, Marie
    et al.
    Uppsala universitet, Institutionen för astronomi och rymdfysik.
    Tjulin, Anders
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutionen för astronomi och rymdfysik.
    Fazakerley, Andrew
    Interferometric Identification of Ion Acoustic Broadband Waves in the Auroral Region: CLUSTER Observations2005Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, nr 21Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 9.
    Becerra Garcia, Marley
    et al.
    Division for Electricity, Uppsala University.
    Cooray, Vernon
    Division for Electricity, Uppsala University.
    On the velocity of positive connecting leaders associated with negative downward lightning leaders2008Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A self-consistent leader propagation model is used to estimate the velocity of upward connecting positive leaders initiated from a tall tower under the influence of downward negative lightning leaders. The propagation of upward connecting leaders has been found to be influenced not only by the average velocity of the downward leader but also by the prospective return stroke current, the lateral position of the downward leader channel as well as by the ambient electric field. This result show that the velocity and propagation time of upward connecting positive leaders change from flash to flash due to the variations in these parameters.

  • 10.
    Behlke, Rico
    et al.
    Uppsala universitet, Institutionen för astronomi och rymdfysik.
    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 shock2003Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 30, nr 4Artikkel i tidsskrift (Fagfellevurdert)
  • 11.
    Block, Lars P
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Mozer, F.S.
    Pedersen, A.
    Potemra, T.A.
    Zanetti, L.J.
    Electric field measurements on Viking - 1st results1987Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 14, s. 435-438Artikkel i tidsskrift (Fagfellevurdert)
  • 12.
    Blomberg, Lars G.
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    High-Latitude Convection Patterns For Various Large-Scale Field-Aligned Current Configurations1991Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 18, nr 4, s. 717-720Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The large-scale field-aligned current system for persistent northward interplanetary magnetic field (IMF) is typically different from that for persistent southward IMF. One characteristic difference is that for northward IMF there is often a large-scale field-aligned current system poleward of the main auroral oval. This current system (the NBZ current) typically occupies a large fraction of the region poleward of the region 1 and 2 currents. The present paper models the high-latitude convection as a function of the large-scale field-aligned currents. In particular, a possible evolution of the convection pattern as the current system changes from a typical configuration for southward IMF to a configuration representing northward IMF (or vice versa) is presented. Depending on additional assumptions, for example about the y-component of the IMF, the convection pattern could either turn directly from a two-cell type to a four-cell type, or a three-cell type pattern could show up as an intermediate state. An interesting although rather surprising result of this study is that different ways of balancing the NBZ currents has a minor influence on the large-scale convection pattern.

  • 13. Boardsen, Scott A.
    et al.
    Sundberg, Torbjorn
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Slavin, James A.
    Anderson, Brian J.
    Korth, Haje
    Solomon, Sean C.
    Blomberg, Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Observations of Kelvin-Helmholtz waves along the dusk-side boundary of Mercury's magnetosphere during MESSENGER's third flyby2010Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, artikkel-id L12101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During the third MESSENGER flyby of Mercury on 29 September 2009, 15 crossings of the dusk-side magnetopause were observed in the magnetic field data over a 2-min period, during which the spacecraft traveled a distance of 0.2 R-M (where R-M is Mercury's radius). The quasi-periodic nature of the magnetic field variations during the crossings, the characteristic time separations of similar to 16 s between pairs of crossings, and the variations of the magnetopause normal directions indicate that the signals are likely the signature of surface waves highly steepened at their leading edge that arose from the Kelvin-Helmholtz instability. At Earth, the Kelvin-Helmholtz instability is believed to lead to the turbulent transport of solar wind plasma into Earth's plasma sheet. This solar wind entry mechanism could also be important at Mercury. Citation: Boardsen, S. A., T. Sundberg, J. A. Slavin, B. J. Anderson, H. Korth, S. C. Solomon, and L. G. Blomberg (2010), Observations of Kelvin-Helmholtz waves along the dusk-side boundary of Mercury's magnetosphere during MESSENGER's third flyby, Geophys. Res. Lett., 37, L12101, doi: 10.1029/2010GL043606.

  • 14. Boehm, M. H.
    et al.
    CLEMMONS, J
    WAHLUND, JE
    ERIKSSON, A
    ELIASSON, L
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    KINTNER, P
    HOFNER, H
    Observations of an  upward-directed electron beam with the perpendicular temperature of the cold ionosphere1995Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 22, s. 2103-2106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Freja TESP electron spectrometer has repeatedly observed similar to 100 eV - 1 keV upward-directed, anti-field-aligned electron beams near 1700 km altitude in the auroral zone. A particularly intense event, at energies up to 2 keV, is described. The beam perpendicular temperature T perpendicular to(e)), was as low as 0.1-0.2 eV at 100-200 eV parallel energy. The 10-15 s period of upward fluxes was coincident with a low density (similar to 10 cm(-3)) period and a similar to 5 keV ion conic. Strong low frequency waves and the lack of any downward motion in the simultaneously observed ion conic suggest a strong element of wave acceleration, while electric field and ion loss cone measurements provide limited evidence of potential acceleration to a fraction of the observed energies.

  • 15.
    Brandefelt, Jenny
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Otto-Bliesner, B. L.
    Equilibration and variability in a Last Glacial Maximum climate simulation with CCSM32009Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present results from a 1862 year simulation of the Last Glacial Maximum (LGM) with the Community Climate System Model version 3 (CCSM3). A quasi steady state is reached after approximately 100 years of integration when the initial cooling trend in the annual global mean atmospheric surface temperature (T-s) levels off and even reverses. After another 150 years of integration the climate continues to cool and reaches a new equilibrium after a total of 800 years of integration. The cause of the continued adjustment of the climate to LGM forcing and boundary conditions is found in the abyssal ocean which is cooling at a rate decreasing from 0.15 degrees C per century until the new equilibrium is reached. The new equilibrium differs substantially from the first quasi steady state with 1.1 degrees C colder global mean Ts and regional differences of 5-15 degrees C in the North Atlantic region and a 30% reduction of the strength of the Atlantic meridional overturning circulation (AMOC). Further, the variability in the global mean Ts is significantly larger in the new equilibrium. This variability is associated with coupled ocean-atmosphere-sea ice variations in the North Atlantic region. Citation: Brandefelt, J., and B. L. Otto-Bliesner (2009), Equilibration and variability in a Last Glacial Maximum climate simulation with CCSM3, Geophys. Res. Lett., 36, L19712, doi: 10.1029/2009GL040364.

  • 16.
    Brethouwer, Geert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Lindborg, Erik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Passive scalars in stratified turbulence2008Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Statistics of a passive scalar (or tracer) with a horizontal mean gradient in randomly forced and strongly stratified turbulence are investigated by numerical simulations. We observe that horizontal isotropy of the passive scalar spectrum is satisfied in the inertial range. The spectrum has the form E-theta(k(h)) = C-theta epsilon theta epsilon(-1/3)(K) k(h)(-5/3), where epsilon(theta), epsilon(K) are the dissipation of scalar variance and kinetic energy respectively, and C-theta similar or equal to 0.5 is a constant. This spectrum is consistent with atmospheric measurements in the mesoscale range with wavelengths 1 - 500 km. We also calculate the fourth-order passive scalar structure function and show that intermittency effects are present in stratified turbulence.

  • 17. Breuillard, H.
    et al.
    Le Contel, O.
    Retino, A.
    Chasapis, A.
    Chust, T.
    Mirioni, L.
    Graham, D. B.
    Wilder, F. D.
    Cohen, I.
    Vaivads, Andris
    Khotyaintsev, Yu V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Burch, J. L.
    Torbert, R. B.
    Ergun, R. E.
    Goodrich, K. A.
    Macri, J.
    Needell, J.
    Chutter, M.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Plaschke, F.
    Fischer, D.
    Leinweber, H. K.
    Anderson, B. J.
    Le, G.
    Slavin, J. A.
    Kepko, E. L.
    Baumjohann, W.
    Mauk, B.
    Fuselier, S. A.
    Nakamura, R.
    Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 14, s. 7279-7286Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 18.
    Burch, J. L.
    et al.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Cassak, P. A.
    Univ Virginia, Dept Phys & Astron, Morgantown, WV USA..
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX USA..
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX 78238 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA..
    Hwang, K. -J
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Allen, R. C.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Chen, L. -J
    Wang, S.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Gershman, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Observ Paris, Lab Phys Plasmas, CNRS,Ecole Polytech,UPMC Univ Paris 06, Paris, France..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Planetary Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Planetary Sci, Los Angeles, CA USA..
    Wilder, F. D.
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Hesse, M.
    Univ Bergen, Dept Phys & Technol, Bergen, Norway..
    Drake, J. F.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Swisdak, M.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Price, L. M.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Pollock, C. J.
    Denali Sci, Healy, AK USA..
    Denton, R. E.
    Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA..
    Newman, D. L.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Localized Oscillatory Energy Conversion in Magnetopause Reconnection2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 3, s. 1237-1245Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. High-resolution measurements of plasmas and fields are used to identify highly localized (similar to 15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J . E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X-line. This difference is explained in terms of channels for the out-of-plane current (agyrotropic electrons at the stagnation point and guide field-aligned electrons at the X-line).

  • 19. Callaghan, Terry V.
    et al.
    Bergholm, Fredrik
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk Analys och Datalogi, NADA.
    Christensen, Torben R.
    Jonasson, Christer
    Kokfelt, Ulla
    Johansson, Margareta
    A new climate era in the sub-Arctic: Accelerating climate changes and multiple impacts2010Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, nr 14, s. L14705-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Climate warming in the Swedish sub-Arctic since 2000 has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930' s and early 1940' s, and has significantly crossed the 0 degrees C mean annual temperature threshold which causes many cryospheric and ecological impacts. The accelerating temperature increase trend has driven similar trends in the century-long increase in snow thickness, loss of lake ice, increases in active layer thickness, lake water TOC (total organic carbon) concentrations and the assemblages of diatoms, and changes in tree-line location and plant community structure. Some of these impacts were not evident in the first warm period of the 20th Century. Changes in climate are associated with reduced temperature variability, particularly loss of cold winters and cool summers, and an increase in extreme precipitation events that cause mountain slope instability and infrastructure failure. The long term records of multiple, local environmental factors compiled here for the first time provide detailed information for adaptation strategy development while dramatic changes in an environment particularly vulnerable to climate change highlight the need to adopt global mitigation strategies.

  • 20. Cao, D.
    et al.
    Fu, H. S.
    Cao, J. B.
    Wang, T. Y.
    Graham, D. B.
    Chen, Z. Z.
    Peng, F. Z.
    Huang, S. Y.
    Khotyaintsev, Y. V.
    Andre, M.
    Russell, C. T.
    Giles, B. L.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Torbert, R. B.
    Ergun, R. E.
    Le Contel, O.
    Burch, J. L.
    MMS observations of whistler waves in electron diffusion region2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 9, s. 3954-3962Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Whistler waves that can produce anomalous resistivity by affecting electrons' motion have been suggested as one of the mechanisms responsible for magnetic reconnection in the electron diffusion region (EDR). Such type of waves, however, has rarely been observed inside the EDR so far. In this study, we report such an observation by Magnetospheric Multiscale (MMS) mission. We find large-amplitude whistler waves propagating away from the X line with a very small wave-normal angle. These waves are probably generated by the perpendicular temperature anisotropy of the -300eV electrons inside the EDR, according to our analysis of dispersion relation and cyclotron resonance condition; they significantly affect the electron-scale dynamics of magnetic reconnection and thus support previous simulations.

  • 21. Cattell, C.
    et al.
    Breneman, A.
    Colpitts, C.
    Dombeck, J.
    Thaller, S.
    Tian, S.
    Wygant, J.
    Fennell, J.
    Hudson, M. K.
    Ergun, Robert
    Russell, C. T.
    Torbert, Roy
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Burch, J.
    Dayside response of the magnetosphere to a small shock compression: Van Allen Probes, Magnetospheric MultiScale, and GOES-132017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 17, s. 8712-8720, artikkel-id L074895Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Observations from Magnetospheric MultiScale (similar to 8 Re) and Van Allen Probes (similar to 5 and 4 Re) show that the initial dayside response to a small interplanetary shock is a double-peaked dawnward electric field, which is distinctly different from the usual bipolar (dawnward and then duskward) signature reported for large shocks. The associated ExB flow is radially inward. The shock compressed the magnetopause to inside 8 Re, as observed by Magnetospheric MultiScale (MMS), with a speed that is comparable to the ExB flow. The magnetopause speed and the ExB speeds were significantly less than the propagation speed of the pulse from MMS to the Van Allen Probes and GOES-13, which is consistent with the MHD fast mode. There were increased fluxes of energetic electrons up to several MeV. Signatures of drift echoes and response to ULF waves also were seen. These observations demonstrate that even very weak shocks can have significant impact on the radiation belts. Plain Language Summary Very fast moving clouds of charged particles are ejected from the Sun when it is active. Shock waves often develop at the cloud front as it plows through the solar wind. When the shock hits the Earth's magnetic field, it can push the Earth's magnetic shield inside the distance where many communication and weather satellites orbit. The energy associated with the shock can also very rapidly increase the energy of electrons trapped in the Earth's magnetic field in the Van Allen Radiation belts. These electrons can damage satellites. We have used four satellites arrayed at different locations on the dayside of the Earth's magnetic field to show, for the first time, that small shocks have a different effect than the large shocks that are usually studied but that even small shocks can produce relativistic electrons.

  • 22. Cazzola, E.
    et al.
    Innocenti, M. E.
    Goldman, M. V.
    Newman, D. L.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Lapenta, G.
    On the electron agyrotropy during rapid asymmetric magnetic island coalescence in presence of a guide field2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 15, s. 7840-7849Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an analysis of the properties of the electron velocity distribution during island coalescence in asymmetric reconnection with and without guide field. In a previous study, three main domains were identified, in the case without guide field, as X, D, and M regions featuring different reconnection evolutions. These regions are also identified here in the case with guide field. We study the departure from isotropic and gyrotropic behavior by means of different robust detection algorithms proposed in the literature. While in the case without guide field these metrics show an overall agreement, when the guide field is present, a discrepancy in the agyrotropy within some relevant regions is observed, such as at the separatrices and inside magnetic islands. Moreover, in light of the new observations from the Multiscale MagnetoSpheric mission, an analysis of the electron velocity phase-space in these domains is presented.

  • 23. Chen, L. -J
    et al.
    Wang, S.
    Hesse, M.
    Ergun, R. E.
    Moore, T.
    Giles, B.
    Bessho, N.
    Russell, C.
    Burch, J.
    Torbert, R. B.
    Genestreti, K. J.
    Paterson, W.
    Pollock, C.
    Lavraud, B.
    Le Contel, O.
    Strangeway, R.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 12, s. 6230-6238Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Kinetic structures of electron diffusion regions (EDRs) under finite guide fields in magnetotail reconnection are reported. The EDRs with guide fields 0.14–0.5 (in unit of the reconnecting component) are detected by the Magnetospheric Multiscale spacecraft. The key new features include the following: (1) cold inflowing electrons accelerated along the guide field and demagnetized at the magnetic field minimum while remaining a coherent population with a low perpendicular temperature, (2) wave fluctuations generating strong perpendicular electron flows followed by alternating parallel flows inside the reconnecting current sheet under an intermediate guide field, and (3) gyrophase bunched electrons with high parallel speeds leaving the X-line region. The normalized reconnection rates for the three EDRs range from 0.05 to 0.3. The measurements reveal that finite guide fields introduce new mechanisms to break the electron frozen-in condition.

  • 24.
    Cvetkovic, Vladimir
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik, Vattenvårdsteknik.
    Diffusion-controlled tracer retention in crystalline rock on the field scale2010Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, s. L13401-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tracer retention is a key process for the barrier function of crystalline rock to any contaminant. Here we investigate the nature of retention mechanisms and their field-scale parametrization using results of a comprehensive tracer transport experiment in crystalline rock on the field scale (Aspo Hard Rock Laboratory, Sweden). A method for identifying dominant retention mechanisms and inferring key parameters on the site scale is presented. Taking advantage of multiple tracer tests with a wide range of sorption affinities, retention is shown to be diffusion-controlled. For the considered site, robust features of tracer migration can be reasonably well predicted within a rock volume on at least 200 m scale, by combining independent information with a simple model.

  • 25. Dahlgren, H.
    et al.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lanchester, B. S.
    Monoenergetic high-energy electron precipitation in thin auroral filaments2012Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, nr 20, s. L20101-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The energy distribution of the electron precipitation responsible for extremely narrow (70 m) and dynamic auroral filaments is found to be sharply peaked at around 8 keV. The events were captured with high resolution low-light optical imagers located near Tromso, Norway. The method uses imaging in two emissions which have different energy dependent responses to auroral electron precipitation. The key feature of the events was that no difference in the altitude of the two emissions was detected, nor any time-of-flight dispersion, thus leading to the conclusion that the filaments were caused by monoenergetic precipitation. Comparisons with an electron transport and ion chemistry model show that the high energy filaments were embedded in a region of lower energy precipitation of about 4 keV. There is currently no consistent theory to explain the characteristics of the observed auroral structures.

  • 26.
    Dahlgren, Hanna
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. University of Southampton, United Kingdom .
    Lanchester, B. S.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Coexisting structures fromhigh- and low-energy precipitation in fine-scale aurora2015Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 5, s. 1290-1296Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution multimonochromatic measurements of auroral emissions have revealed the first optical evidence of coexisting small-scale auroral features resulting from separate high- and low-energy populations of precipitating electrons on the same field line. The features exhibit completely separate motion and morphology. From emission ratios and ion chemistry modeling, the average energy and energy flux of the precipitation is estimated. The high-energy precipitation is found to form large pulsating patches of 0.1Hz with a 3Hz modulation, and nonpulsating coexisting discrete auroral filaments. The low-energy precipitation is observed simultaneously on the same field line as discrete filaments with no pulsation. The simultaneous structures do not interact, and they drift with different speeds in different directions. We suggest that the high- and low-energy electron populations are accelerated by separate mechanisms, at different distances from Earth. The small-scale structures could be caused by local instabilities above the ionosphere.

  • 27. Deca, Jan
    et al.
    Divin, Andrey
    Wang, Xu
    Lembege, Bertrand
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST). KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Horanyi, Mihaly
    Lapenta, Giovanni
    Three-dimensional full-kinetic simulation of the solar wind interaction with a vertical dipolar lunarmagnetic anomaly2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 9, s. 4136-4144Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A detailed understanding of the solar wind interaction with lunar magnetic anomalies (LMAs) is essential to identify its implications for lunar exploration and to enhance our physical understanding of the particle dynamics in a magnetized plasma. We present the first three-dimensional full-kinetic electromagnetic simulation case study of the solar wind interaction with a vertical dipole, resembling a medium-size LMA. In contrast to a horizontal dipole, we show that a vertical dipole twists its field lines and cannot form a minimagnetosphere. Instead, it creates a ring-shaped weathering pattern and reflects up to 21% (four times more as compared to the horizontal case) of the incoming solar wind ions electrostatically through the normal electric field formed above the electron shielding region surrounding the cusp. This work delivers a vital piece to fully comprehend and interpret lunar observations, as we find the amount of reflected ions to be a tracer for the underlying field structure.

  • 28. Divin, A.
    et al.
    Semenov, V.
    Korovinskiy, D.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Deca, J.
    Olshevsky, V.
    Lapenta, G.
    A new model for the electron pressure nongyrotropy in the outer electron diffusion region2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 20, s. 10565-10573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a new model to describe the electron pressure nongyrotropy inside the electron diffusion region (EDR) in an antiparallel magnetic reconnection scenario. A combination of particle-in-cell simulations and analytical estimates is used to identify such a component of the electron pressure tensor in the rotated coordinates, which is nearly invariant along the outflow direction between the X line and the electron remagnetization points in the outer EDR. It is shown that the EDR two-scale structure (inner and outer parts) is formed due to superposition of the nongyrotropic meandering electron population and gyrotropic electron population with large anisotropy parallel to the magnetic field upstream of the EDR. Inside the inner EDR the influence of the pressure anisotropy can largely be ignored. In the outer EDR, a thin electron layer with electron flow speed exceeding the E x B drift velocity is supported by large-momentum flux produced by the electron pressure anisotropy upstream of the EDR. We find that this fast electron exhaust flow with |V(e)xB|>|E| is in fact a constituent part of the EDR, a finding which will steer the interpretation of the Magnetospheric Multiscale Mission (MMS) data.

  • 29.
    Eastwood, J. P.
    et al.
    Imperial Coll London, Blackett Lab, London, England..
    Mistry, R.
    Imperial Coll London, Blackett Lab, London, England..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Schwartz, S. J.
    Imperial Coll London, Blackett Lab, London, England.;Univ Colorado, Dept Astrophys & Planetary Sci, LASP, Boulder, CO 80309 USA..
    Ergun, R. E.
    Univ Colorado, Dept Astrophys & Planetary Sci, LASP, Boulder, CO 80309 USA..
    Drake, J. F.
    Univ Maryland, Dept Phys, College Pk, MD 20742 USA.;Univ Maryland, Inst Phys Sci & Technol, College Pk, MD 20742 USA..
    Oieroset, M.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Stawarz, J. E.
    Imperial Coll London, Blackett Lab, London, England..
    Goldman, M. V.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Haggerty, C.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA.;Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Gershman, D. J.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Torbert, R. B.
    Univ Chicago, Dept Astron & Astrophys, 5640 S Ellis Ave, Chicago, IL 60637 USA.;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Guide Field Reconnection: Exhaust Structure and Heating2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 10, s. 4569-4577Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetospheric Multiscale observations are used to probe the structure and temperature profile of a guide field reconnection exhaust similar to 100 ion inertial lengths downstream from the X-line in the Earth's magnetosheath. Asymmetric Hall electric and magnetic field signatures were detected, together with a density cavity confined near 1 edge of the exhaust and containing electron flow toward the X-line. Electron holes were also detected both on the cavity edge and at the Hall magnetic field reversal. Predominantly parallel ion and electron heating was observed in the main exhaust, but within the cavity, electron cooling and enhanced parallel ion heating were found. This is explained in terms of the parallel electric field, which inhibits electron mixing within the cavity on newly reconnected field lines but accelerates ions. Consequently, guide field reconnection causes inhomogeneous changes in ion and electron temperature across the exhaust.

  • 30. Eastwood, J. P.
    et al.
    Phan, T. D.
    Cassak, P. A.
    Gershman, D. J.
    Haggerty, C.
    Malakit, K.
    Shay, M. A.
    Mistry, R.
    Oieroset, M.
    Russell, C. T.
    Slavin, J. A.
    Argall, M. R.
    Avanov, L. A.
    Burch, J. L.
    Chen, L. J.
    Dorelli, J. C.
    Ergun, R. E.
    Giles, B. L.
    Khotyaintsev, Y.
    Lavraud, B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Moore, T. E.
    Nakamura, R.
    Paterson, W.
    Pollock, C.
    Strangeway, R. J.
    Torbert, R. B.
    Wang, S.
    Ion-scale secondary flux ropes generated by magnetopause reconnection as resolved by MMS2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4716-4724Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New Magnetospheric Multiscale (MMS) observations of small-scale (similar to 7 ion inertial length radius) flux transfer events (FTEs) at the dayside magnetopause are reported. The 10 km MMS tetrahedron size enables their structure and properties to be calculated using a variety of multispacecraft techniques, allowing them to be identified as flux ropes, whose flux content is small (similar to 22 kWb). The current density, calculated using plasma and magnetic field measurements independently, is found to be filamentary. Intercomparison of the plasma moments with electric and magnetic field measurements reveals structured non-frozen-in ion behavior. The data are further compared with a particle-in-cell simulation. It is concluded that these small-scale flux ropes, which are not seen to be growing, represent a distinct class of FTE which is generated on the magnetopause by secondary reconnection.

  • 31. Ergun, R. E.
    et al.
    Chen, L. -J
    Wilder, F. D.
    Ahmadi, N.
    Eriksson, S.
    Usanova, M. E.
    Goodrich, K. A.
    Holmes, J. C.
    Sturner, A. P.
    Malaspina, D. M.
    Newman, D. L.
    Torbert, R. B.
    Argall, M. R.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Burch, J. L.
    Webster, J. M.
    Drake, J. F.
    Price, L.
    Cassak, P. A.
    Swisdak, M.
    Shay, M. A.
    Graham, D. B.
    Strangeway, R. J.
    Russell, C. T.
    Giles, B. L.
    Dorelli, J. C.
    Gershman, D.
    Avanov, L.
    Hesse, M.
    Lavraud, B.
    Le Contel, O.
    Retino, A.
    Phan, T. D.
    Goldman, M. V.
    Stawarz, J. E.
    Schwartz, S. J.
    Eastwood, J. P.
    Hwang, K. -J
    Nakamura, R.
    Wang, S.
    Drift waves, intense parallel electric fields, and turbulence associated with asymmetric magnetic reconnection at the magnetopause2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 7, s. 2978-2986Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large-amplitude parallel electric fields (E-||). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large-amplitude (similar to 100mV/m) E-|| in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process.

  • 32. Ergun, R. E.
    et al.
    Goodrich, K. A.
    Wilder, F. D.
    Ahmadi, N.
    Holmes, J. C.
    Eriksson, S.
    Stawarz, J. E.
    Nakamura, R.
    Genestreti, K. J.
    Hesse, M.
    Burch, J. L.
    Torbert, R. B.
    Phan, T. D.
    Schwartz, S. J.
    Eastwood, J. P.
    Strangeway, R. J.
    Le Contel, O.
    Russell, C. T.
    Argall, M. R.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Chen, L. J.
    Cassak, P. A.
    Giles, B. L.
    Dorelli, J. C.
    Gershman, D.
    Leonard, T. W.
    Lavraud, B.
    Retino, A.
    Matthaeus, W.
    Vaivads, A.
    Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 8, s. 3338-3347Artikkel i tidsskrift (Fagfellevurdert)
    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 |E| >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 (fci) provide the majority net positive J · E. Large-amplitude parallel E events with frequencies above fci to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration.

  • 33. Ergun, R E
    et al.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Andre, M.
    et al.,
    Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 11, s. 5626-5634Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earth's magnetopause. The observed waves have parallel electric fields (E-||) with amplitudes on the order of 100mV/m and display nonlinear characteristics that suggest a possible net E-||. These waves are observed within the ion diffusion region and adjacent to (within several electron skin depths) the electron diffusion region. They are in or near the magnetosphere side current layer. Simulation results support that the strong electrostatic linear and nonlinear wave activities appear to be driven by a two stream instability, which is a consequence of mixing cold (<10eV) plasma in the magnetosphere with warm (similar to 100eV) plasma from the magnetosheath on a freshly reconnected magnetic field line. The frequent observation of these waves suggests that cold plasma is often present near the magnetopause.

  • 34. Erickson, P. J.
    et al.
    Matsui, H.
    Foster, J. C.
    Torbert, R. B.
    Ergun, R. E.
    Khotyaintsev, Yu. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Argall, M. R.
    Farrugia, C. J.
    Paulson, K. W.
    Strangeway, R. J.
    Magnes, W.
    Multipoint MMS observations of fine-scale SAPS structure in the inner magnetosphere2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 14, s. 7294-7300Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present detailed observations of dynamic, fine-scale inner magnetosphere-ionosphere coupling at approximate to 3.9R(E) in the Region 2 Birkeland field-aligned current (FAC). We find that observed electrodynamic spatial/temporal scales are primarily characteristic of magnetically mapped ionospheric structure. On 15 September 2015, conjugate Magnetospheric Multiscale (MMS) spacecraft and Millstone Hill radar observations show plasmasphere boundary region subauroral polarization stream (SAPS) electric fields at L = 4.0-4.2 near 21 MLT. MMS observations reveal high-altitude approximate to 1mV/m fine-scale radial and azimuthal electric field perturbations over 0.15L with high spatial coherence over 2-3min and show outward motion within a broader FAC of approximate to 0.12A/m(2). Our analysis shows that MMS electric field fluctuations are most likely reflective of SAPS ionospheric structure at scales of approximate to 22km and with ionospheric closure of small-scale filamentary FAC perturbations. The results highlight the ionosphere's importance in regulating fine-scale magnetosphere-ionosphere structure.

  • 35.
    Eriksson, Elin
    et al.
    Swedish Inst Space Phys, Uppsala, Sweden.;Uppsala Univ, Dept Phys & Astron, Uppsala, Sweden..
    Vaivads, Andris
    Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, Daniel B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Divin, Andrey
    Swedish Inst Space Phys, Uppsala, Sweden.;St Petersburg State Univ, Dept Phys, St Petersburg, Russia..
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Yordanova, Emiliya
    Swedish Inst Space Phys, Uppsala, Sweden..
    Andre, Mats
    Swedish Inst Space Phys, Uppsala, Sweden..
    Giles, Barbara L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Pollock, Craig J.
    Denali Sci LLC, Healy, AK USA..
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Le Contel, Olivier
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Ecole Polytech,CNRS,Lab Phys Plasmas, Paris, France..
    Torbert, Roy B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Ergun, Robert E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Electron Energization at a Reconnecting Magnetosheath Current Sheet2018Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 16, s. 8081-8090Artikkel i tidsskrift (Fagfellevurdert)
    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 (similar to 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. Plain Language Summary Magnetic reconnection is an important physical energy conversion process in astrophysical and laboratory plasmas. The easiest place to analyze magnetic reconnection is in near-Earth space. Due to lack of sufficient electron resolution of previous spacecraft missions, there are many unanswered questions regarding electron heating and acceleration processes at small scales. In particular, the regime where thermal pressure dominates over magnetic pressure, the most common state of plasmas in the Universe, is little explored. In this letter we study such a regime using the four-spacecraft Magnetospheric Multiscale mission. We analyze a reconnecting current sheet in the magnetosheath. We show that electrons are energized by a parallel potential, similar to what has been observed in the different plasma regimes the magnetopause and magnetotail. Thus, despite different plasma conditions, a similar acceleration mechanism and corresponding heating of electrons is occurring in all these regions.

  • 36.
    Eriksson, Elin
    et al.
    Uppsala universitet, Institutionen för fysik och astronomi.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri. V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyayintsev, V. M.
    Taras Shevchenko Natl Univ Kyiv, Dept Theoret Phys, Kiev, Ukraine..
    Andre, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Statistics and accuracy of magnetic null identification in multispacecraft data2015Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, s. 6883-6889Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 37. Eriksson, S.
    et al.
    Lavraud, B.
    Wilder, F. D.
    Stawarz, J. E.
    Giles, B. L.
    Burch, J. L.
    Baumjohann, W.
    Ergun, R. E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Magnes, W.
    Pollock, C. J.
    Russell, C. T.
    Saito, Y.
    Strangeway, R. J.
    Torbert, R. B.
    Gershman, D. J.
    Khotyaintsev, Yu. V.
    Dorelli, J. C.
    Schwartz, S. J.
    Avanov, L.
    Grimes, E.
    Vernisse, Y.
    Sturner, A. P.
    Phan, T. D.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Moore, T. E.
    Paterson, W. R.
    Goodrich, K. A.
    Magnetospheric Multiscale observations of magnetic reconnection associated with Kelvin-Helmholtz waves2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 11, s. 5606-5615Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The four Magnetospheric Multiscale (MMS) spacecraft recorded the first direct evidence of reconnection exhausts associated with Kelvin-Helmholtz (KH) waves at the duskside magnetopause on 8 September 2015 which allows for local mass and energy transport across the flank magnetopause. Pressure anisotropy-weighted Walen analyses confirmed in-plane exhausts across 22 of 42 KH-related trailing magnetopause current sheets (CSs). Twenty-one jets were observed by all spacecraft, with small variations in ion velocity, along the same sunward or antisunward direction with nearly equal probability. One exhaust was only observed by the MMS-1,2 pair, while MMS-3,4 traversed a narrow CS (1.5 ion inertial length) in the vicinity of an electron diffusion region. The exhausts were locally 2-D planar in nature as MMS-1,2 observed almost identical signatures separated along the guide-field. Asymmetric magnetic and electric Hall fields are reported in agreement with a strong guide-field and a weak plasma density asymmetry across the magnetopause CS.

  • 38.
    Farrugia, C. J.
    et al.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys, Toulouse, France.;CNRS, Toulouse, France..
    Torbert, R. B.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Argall, M.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Kacem, I.
    Univ Toulouse, Inst Rech Astrophys, Toulouse, France..
    Yu, W.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Alm, L.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Russell, C. T.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Shuster, J.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Dorelli, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Eastwood, J. P.
    Imperial Coll London, Blackett Lab, London, England..
    Ergun, R. E.
    Univ Colorado, Boulder, CO 80309 USA..
    Fuselier, S.
    Southwest Res Inst, San Antonio, TX USA.;Univ Texas San Antonio, Dept Space Sci, San Antonio, TX USA..
    Gershman, D.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Swedish Institute of Space Physics, Sweden.
    Matsui, H.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Swedish Institute of Space Physics, Sweden.
    Phan, T. D.
    Space Sci Lab, Berkeley, CA USA..
    Paulson, K.
    Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Pollock, C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Los Angeles, CA USA..
    Magnetospheric Multiscale Mission observations and non-force free modeling of a flux transfer event immersed in a super-Alfvenic flow2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 12, s. 6070-6077Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyze plasma, magnetic field, and electric field data for a flux transfer event (FTE) to highlight improvements in our understanding of these transient reconnection signatures resulting from high-resolution data. The similar to 20 s long, reverse FTE, which occurred south of the geomagnetic equator near dusk, was immersed in super-Alfvenic flow. The field line twist is illustrated by the behavior of flows parallel/perpendicular to the magnetic field. Four-spacecraft timing and energetic particle pitch angle anisotropies indicate a flux rope (FR) connected to the Northern Hemisphere and moving southeast. The flow forces evidently overcame the magnetic tension. The high-speed flows inside the FR were different from those outside. The external flows were perpendicular to the field as expected for draping of the external field around the FR. Modeling the FR analytically, we adopt a non-force free approach since the current perpendicular to the field is nonzero. It reproduces many features of the observations.

  • 39.
    Feldstein, Y. I.
    et al.
    IZMIRIAN, Troitsk, Russia.
    Levitin, A. E.
    IZMIRIAN, Troitsk, Russia.
    Gromova, L. I.
    IZMIRIAN, Troitsk, Russia.
    DREMUHINA, LA
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lindqvist, Per-Arne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Electromagnetic weather at 100 km altitude on 3 August 19861994Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 21, s. 2095-2098Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electromagnetic weather at high altitudes above the Earth’s surface is determined by the transport of ionospheric plasma, which in turn is governed by the magnitude as well as the direction of the electric and magnetic fields. Different models [Levitin et al., 1984; Friis-Christensen et al., 1985; Mishin, 1990] have been proposed that allow an estimation of the electromagnetic parameters of the upper atmosphere, given a knowledge of the magnitude and orientation of the interplanetary magnetic field. Here we use one such model to estimate the global convection pattern and its temporal evolution during a pass of the Swedish satellite Viking over the northern polar cap. The model predictions are shown to agree well with the electric and magnetic fields measured along the satellite trajectory. The good agreement implies that the model can be used to reconstruct, with reasonable confidence, the large-scale distribution of electric and magnetic fields and their time-variation in the entire auroral ionosphere.

  • 40.
    Flache, D.
    et al.
    University of Florida, Gainesville, USA.
    Rakov, V. A.
    University of Florida, Gainesville, USA.
    Heidler, F.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Zischank, W.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Thottappillil, Rajeev
    Uppsala University.
    Initial-stage pulses in upward lightning: Leader/return stroke versus M-component mode of charge transfer to ground2008Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, nr 13, s. L13812-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyzed high-speed video images and corresponding current records for eight upward lightning flashes initiated by the Peissenberg tower (160 m) in Germany. These flashes contained a total of 33 measurable initial stage (IS) current pulses, which are superimposed on steady IS currents. Seven IS pulses had relatively short (< 8 mu s) 10-to-90% risetimes and 26 IS pulses had relatively long (> 8 mu s) risetimes. Six (86%) of seven IS current pulses with shorter risetimes each developed in a newly-illuminated branch, and 25 (96%) of 26 IS pulses with longer risetimes occurred in already luminous (current-carrying) channels. These results support the hypothesis that longer risetimes are indicative of the M-component mode of charge transfer to ground, while shorter risetimes are associated with the leader/return stroke mode. Similar results were obtained for M-component pulses that are superimposed on continuing currents following return-stroke pulses.

  • 41.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Cao, J. B.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Cao, D.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Wang, Z.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China.
    Vaivads, Andris
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik. Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA.
    Huang, S. Y.
    Wuhan Univ, Sch Elect & Informat, Wuhan, Hubei, Peoples R China.
    Evidence of Magnetic Nulls in Electron Diffusion Region2019Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, nr 1, s. 48-54Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theoretically, magnetic reconnection—the process responsible for solar flares and magnetospheric substorms—occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient techniques and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed First‐Order Taylor Expansion (FOTE) Expansion technique. We investigate 12 EDR candidates at the Earth's magnetopause and find radial nulls (X‐lines) in all of them. In some events, spacecraft are only 3 km (one electron inertial length) away from the null. We reconstruct the magnetic topology of these nulls and find it agrees well with theoretical models. These nulls, as reconstructed for the first time inside the EDR by the FOTE technique, indicate that the EDR is active and the reconnection process is ongoing.

    Plain Language Summary: Magnetic reconnection is a key process responsible for many explosive phenomena in nature such as solar flares and magnetospheric substorms. Theoretically, such process occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is still unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient technique and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed FOTE technique.

  • 42.
    Fu, H. S.
    et al.
    Beihang Univ, Sch Space & Environm, Beijing, Peoples R China..
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    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 reconnection2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 1, s. 37-43Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 43.
    Fu, Huishan
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Huang, S. Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Occurrence rate of earthward-propagating dipolarization fronts2012Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, artikkel-id L10101Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 44.
    Fu, Huishan S.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Fermi and betatron acceleration of suprathermal electrons behind dipolarization fronts2011Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, artikkel-id L16104Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 45.
    Fu, Huishan S.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Huang, S. Y.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Electric structure of dipolarization front at sub-proton scale2012Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, s. L06105-Artikkel i tidsskrift (Fagfellevurdert)
    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. 

  • 46. Gavryushkin, P. N.
    et al.
    Popov, Z. I.
    Litasov, K. D.
    Belonoshko, Anatoly
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Kondenserade materiens teori.
    Gavryushkin, A.
    Stability of B2-type FeS at Earth's inner core pressures2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 16, s. 8435-8440Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using density functional theory, we investigated how substituting sulfur atoms for iron atoms affects the structure and energy of the body centered cubic and hexagonal close-packed iron phases at 350 GPa and at 0 K. We conclude that formation of random (Fe,S) solid solutions is energetically favorable in all intermediate compositions, although the random low-symmetry substitutions cause structural distortion. The (Fe,S) solid solution is nearly as favorable as the mechanical mixture of Fe-hcp and FeS-B2. This finding, in combination with dynamical stability, defines the B2 structure as a strong candidate for the sulfur-bearing phase of the Earth's inner core.

  • 47. Germany, G A
    et al.
    Parks, G K
    Brittnacher, M
    Cumnock, Judy
    Center for Space Sciences, University of Texas at Dallas, Richardson, TX.
    Lummerzheim, D
    Spann, J F
    Chen, L
    Richards, P G
    Rich, F J
    Remote determination of auroral energy characteristics during substorm activity1997Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 24, s. 995-998Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultraviolet auroral images from the Ultraviolet Imager (UVI) onboard the POLAR satellite can be used as quantitative remote diagnostics of the auroral regions, yielding estimates of incident energy characteristics, compositional changes, and other higher order data products. Here incident energy estimates derived from UVI are compared with in situ measurements of the same parameters from an overflight by the DMSP F12 satellite coincident with the UVI image times during substorm activity occurring on May 19, 1996. This event was simultaneously observed by WIND, GEOTAIL, INTERBALL, DMSP and NOAA spacecraft as well as by POLAR.

  • 48. Goodrich, Katherine A.
    et al.
    Ergun, Robert E.
    Wilder, Frederick D.
    Burch, James
    Torbert, Roy
    Khotyaintsev, Yuri
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Russell, Christopher
    Strangeway, Robert
    Magnes, Werner
    Gershman, Daniel
    Giles, Barbara
    Nakamura, Rumi
    Stawarz, Julia
    Holmes, Justin
    Sturner, Andrew
    Malaspina, David M.
    MMS Multipoint electric field observations of small-scale magnetic holes2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 12, s. 5953-5959Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Small-scale magnetic holes (MHs), local depletions in magnetic field strength, have been observed multiple times in the Earth's magnetosphere in the bursty bulk flow (BBF) braking region. This particular subset of MHs has observed scale sizes perpendicular to the background magnetic field (B) less than the ambient ion Larmor radius (rho(i)). Previous observations by Time History of Events and Macroscale Interactions during Substorms (THEMIS) indicate that this subset of MHs can be supported by a current driven by the E x B drift of electrons. Ions do not participate in the E x B drift due to the small-scale size of the electric field. While in the BBF braking region, during its commissioning phase, the Magnetospheric Multiscale (MMS) spacecraft observed a small-scale MH. The electric field observations taken during this event suggest the presence of electron currents perpendicular to the magnetic field. These observations also suggest that these currents can evolve to smaller spatial scales.

  • 49. Graham, D. B.
    et al.
    Khotyaintsev, Yu. V.
    Norgren, C.
    Vaivads, Andris
    Andre, M.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R. E.
    Paterson, W. R.
    Gershman, D. J.
    Giles, B. L.
    Pollock, C. J.
    Dorelli, J. C.
    Avanov, L. A.
    Lavraud, B.
    Saito, Y.
    Magnes, W.
    Russell, C. T.
    Strangeway, R. J.
    Torbert, R. B.
    Burch, J. L.
    Electron currents and heating in the ion diffusion region of asymmetric reconnection2016Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4691-4700Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 50.
    Graham, Daniel B.
    et al.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Khotyaintsev, Yuri V.
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Vaivads, Andris
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    André, Mats
    Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen.
    Electrostatic solitary waves with distinct speeds associated with asymmetric reconnection2015Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 2, s. 215-224Artikkel i tidsskrift (Fagfellevurdert)
    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.

123 1 - 50 of 142
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