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  • 51.
    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    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Electromagnetic weather at 100 km altitude on 3 August 19861994In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 21, p. 2095-2098Article in journal (Refereed)
    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.

  • 52. Feldstein, Y. I.
    et al.
    Levitin, A. E.
    Gromova, L. I.
    Marklund, Göran
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Blomberg, L. G.
    Lindqvist, Per-Arne
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Electromagnetic weather over the high-latitude ionosphere during the aurora in the polar cap1995In: Cosmic research, ISSN 0010-9525, E-ISSN 1608-3075, Vol. 33, p. 326-335Article in journal (Refereed)
  • 53. Feldstein, Y. I.
    et al.
    Levitin, A. E.
    Gromova, L. I.
    Marklund, Göran
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Blomberg, L. G.
    Lindqvist, Per-Arne
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Elektromagnitnaya pogoda nad vysokoshirotnoj ionosferoj vo vremja poljarnogo sijanija v poljarnoj shapke1995In: Kosmicheskie Issledovaniya, Vol. 33, p. 360-370Article in journal (Refereed)
  • 54. Feldstein, Y. I.
    et al.
    Woch, G. J.
    Sandahl, I.
    Blomberg, Lars G.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Meng, C. I.
    Structure of the auroral precipitation region in the dawn sector: relationship to convection reversal boundaries and field-aligned currents2001In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, no 5, p. 495-519Article in journal (Refereed)
    Abstract [en]

    Simultaneous DMSP F7 and Viking satellite measurements of the dawnside high-latitude auroral energy electron and ion precipitation show that the region of the low and middle altitude auroral precipitation consists of three characteristic plasma regimes. The recommendation of the IAGA Working Group IIF/III4 at the IAGA Assembly in Boulder, July 1995 to decouple the nomenclature of ionospheric populations from magnetospheric population is used for their notation. The most equatorial regime is the Diffuse Auroral Zone (DAZ) of diffuse spatially unstructured precipitating electrons. It is generated by the plasma injection to the inner magnetosphere in the nightside and the subsequent drift plasma to the dawnside around the Earth. Precipitating par tides have a hard spectrum with typical energies of electrons and ions of more than 3 keV. In the DAZ, the ion pitch-angle distribution is anisotropic. with the peak near 90 degrees. The next part is the Auroral Oval (AO), a structured electron regime which closely resembles the poleward portion of the nightside auroral oval. The typical electron energy is several keV, and the ion energy is up to 10 keV. Ion distributions are predominantly isotropic. In some cases, this plasma regime may be absent in the prenoon sector. Poleward of the Auroral Oval, there is the Soft Small Scale Luminosity (SSSL) regime. It is caused by structured electron and ion precipitation with typical electron energy of about 0.3 keV and ion energy of about 1 keV. The connection of these low-altitude regimes with plasma domains of the distant magnetosphere is discussed. For mapping of the plasma regimes to the equatorial plane of the magnetosphere, the empirical model by Tsyganenko (1995) and the conceptual model by Alexeev et al. (1996) are used. The DAZ is mapped along the magnetic field lines to the Remnant Layer (RL), which is located in the outer radiation belt region: the zone of structured electrons and isotropic ion precipitation (AO) is mapped to the dawn periphery of the Central Plasma Sheet (CPS); the soft small scale structured precipitation (SSSL) is mapped to the outer magnetosphere close to the magnetopause, i.e. the Low Latitude Boundary Layer (LLBL). In the near-noon sector, earthward fluxes of soft electrons, which cause the Diffuse Red Aurora (DRA), are observed. The ion energies decrease with increasing latitude, The plasma spectra of the DRA regime are analogous to the spectra of the Plasma Mantle (PM). In the dawn sector, the large-scale field-aligned currents flow into the ionosphere at the SSSL latitudes (Region 1) and flow out at the AO or DAZ latitudes (Region 2). In the dawn and dusk sectors, the large-scale Region 1 and Region 2 FAC generation occurs in different plasma domains of the distant magnetosphere. The dawn and dusk FAC connection to the traditional Region 1 and Region 2 has only formal character, as FAC generating in various magnetospheric plasma domains integrate in the same region (Region 1 or Region 2). In the SSSL, there is anti-sunward convection in the DAZ and the AO, there is the sunward convection. At PM latitudes, the convection is controlled by the azimuthal IMF component (By) It is suggested to extend the notation of the plasma pattern boundaries, as proposed by Newell et al. (1996), for the nightside sector of the auroral oval to the dawn sector.

  • 55.
    Figueiredo, Sonia
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution2004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 3, p. 923-934Article in journal (Refereed)
    Abstract [en]

    Based on Astrid-2 satellite data, results are presented from a statistical study on subauroral ion drift (SAID) occurrence. SAID is a subauroral phenomenon characterized by a westward ionospheric ion drift with velocity greater than 1000 m/s, or equivalently, by a poleward-directed electric field with intensity greater than 30 mV/m. SAID events occur predominantly in the premidnight sector, with a maximum probability located within the 20:00 to 23:00 MLT sector, where the most rapid SAID events are also found. They are substorm related, and show first an increase in intensity and a decrease in latitudinal width during the expansion phase, followed by a weakening and widening of the SAID structures during the recovery phase. The potential drop across a SAID structure is seen to remain roughly constant during the recovery phase. The field-aligned current density and the height-integrated Pedersen conductivity distribution associated with the SAID events were calculated. The results reveal that the strongest SAID electric field peaks are associated with the lowest Pedersen conductivity minimum values. Clear modifications are seen in the ionospheric Pedersen conductivity distribution associated with the SAID structure as time evolves: the SAID peak is located on the poleward side of the corresponding region of reduced Pedersen conductivity; the shape of the regions of reduced conductivity is asymmetric, with a steeper poleward edge and a more rounded equatorward edge; the SAID structure becomes less intense and widens with evolution of the substorm recovery phase. From the analysis of the SAID occurrence relative to the mid-latitude trough position, SAID peaks are seen to occur relatively close to the corresponding mid-latitude trough minimum. Both these features show a similar response to magnetospheric disturbances, but on different time scales - with increasing magnetic activity, the SAID structure shows a faster movement towards lower latitudes than that of the mid-latitude trough. From the combined analysis of these results, we conclude that the SAID generation mechanism cannot be regarded either as a pure voltage generator or as a pure current generator, applied to the ionosphere. While the anti-correlation between the width and the peak intensity of the SAID structures with substorm evolution indicates a magnetospheric source acting as a constant voltage generator, the ionospheric modifications and, in particular the reduction in the conductivity for intense SAID structures, are indicative of a constant current system closing through the ionosphere. The ionospheric feedback mechanisms are seen to be of major importance for sustaining and regulating the SAID structures.

  • 56.
    Figueiredo, Sonia
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Johansson, Tommy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Ebihara, Y
    Ejiri, M
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nilsson, H
    Fazakerley, A
    Temporal and spatial evolution of discrete auroral arcs as seen by Cluster2005In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 7, p. 2531-2557Article in journal (Refereed)
    Abstract [en]

    Two event studies are presented in this paper where intense convergent electric fields, with mapped intensities up to 1350 mV/m, are measured in the auroral upward current region by the Cluster spacecraft, at altitudes between 3 and 5 Earth radii. Both events are from May 2003, Southern Hemisphere, with equatorward crossings by the Cluster spacecraft of the pre-midnight auroral oval. Event 1 occurs during the end of the recovery phase of a strong substorm. A system of auroral arcs associated with convergent electric field structures, with a maximum perpendicular potential drop of about similar to 10 kV, and upflowing field-aligned currents with densities of 3 mu A/m(2) (mapped to the ionosphere), was detected at the boundary between the Plasma Sheet Boundary Layer (PSBL) and the Plasma Sheet (PS). The auroral arc structures evolve in shape and in magnitude on a timescale of tens of minutes, merging, broadening and intensifying, until finally fading away after about 50 min. Throughout this time, both the PS region and the auroral arc structure in its poleward part remain relatively fixed in space, reflecting the rather quiet auroral conditions during the end of the substorm. The auroral upward acceleration region is shown for this event to extend beyond 3.9 Earth radii altitude. Event 2 occurs during a more active period associated with the expansion phase of a moderate substorm. Images from the Defense Meteorological Satellite Program (DMSP) F13 spacecraft show that the Cluster spacecraft crossed the horn region of a surge-type aurora. Conjugated with the Cluster spacecraft crossing above the surge horn, the South Pole All Sky Imager recorded the motion and the temporal evolution of an east-west aligned auroral arc, 30 to 50 km wide. Intense electric field variations are measured by the Cluster spacecraft when crossing above the auroral arc structure, collocated with the density gradient at the PS poleward boundary, and coupled to intense upflowing field-aligned currents with mapped densities of up to 20 mu A/m(2). The surge horn consists of multiple arc structures which later merge into one structure and intensify at the PS poleward boundary. The surge horn and the associated PS region moved poleward with a velocity at the ionospheric level of 0.5 km/s, following the large-scale poleward expansion of the auroral oval associated with the substorm expansion phase.

  • 57. Forsyth, C.
    et al.
    Fazakerley, A. N.
    Walsh, A. P.
    Watt, C. E. J.
    Garza, K. J.
    Owen, C. J.
    Constantinescu, D.
    Dandouras, I.
    Fornacon, K. -H
    Lucek, E.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sadeghi, Seyed Soheil
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Khotyaintsev, Y.
    Masson, A.
    Doss, N.
    Temporal evolution and electric potential structure of the auroral acceleration region from multispacecraft measurements2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, no 12, p. A12203-Article in journal (Refereed)
    Abstract [en]

    Bright aurorae can be excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modeling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest that particle acceleration occurs throughout this region. Using multispacecraft observations from Cluster, we have examined two upward current regions on 14 December 2009. Our observations show that the potential difference below C4 and C3 changed by up to 1.7 kV between their respective crossings, which were separated by 150 s. The field-aligned current density observed by C3 was also larger than that observed by C4. The potential drop above C3 and C4 was approximately the same in both crossings. Using a novel technique of quantitively comparing the electron spectra measured by Cluster 1 and 3, which were separated in altitude, we determine when these spacecraft made effectively magnetically conjugate observations, and we use these conjugate observations to determine the instantaneous distribution of the potential drop in the AAR. Our observations show that an average of 15% of the potential drop in the AAR was located between C1 at 6235 km and C3 at 4685 km altitude, with a maximum potential drop between the spacecraft of 500 V, and that the majority of the potential drop was below C3. Assuming a spatial invariance along the length of the upward current region, we discuss these observations in terms of temporal changes and the vertical structure of the electrostatic potential drop and in the context of existing models and previous single- and multispacecraft observations.

  • 58.
    Fälthammar, Carl-Gunne
    et al.
    KTH, Superseded Departments.
    Block, Lars P
    KTH, Superseded Departments.
    Lindqvist, Per-Arne
    KTH, Superseded Departments.
    Marklund, Göran
    KTH, Superseded Departments.
    Pedersen, A.
    Mozer, F. S.
    Preliminary Results from the DC Electric Field Experiment on Viking1987Report (Other academic)
  • 59.
    Fälthammar, Carl-Gunne
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Block, Lars P
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pedersen, A.
    Mozer, F.S.
    Preliminary results from the DC electric fields experiment on Viking1987In: ANNALES GEOPHYSICAE SERIES A-UPPER ATMOSPHERE AND SPACE SCIENCES, ISSN 0755-0685, Vol. 5, p. 171-175Article in journal (Refereed)
  • 60. Graham, D. B.
    et al.
    Khotyaintsev, Yu. V.
    Norgren, C.
    Vaivads, A.
    Andre, M.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    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 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.

  • 61. Graham, D. B.
    et al.
    Khotyaintsev, Yu. V.
    Norgren, C.
    Vaivads, A.
    Andre, M.
    Toledo-Redondo, S.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    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.
    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.

  • 62. Gustafsson, Georg
    et al.
    Andre, M.
    Carozzi, T.
    Eriksson, A. I.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory.
    Grard, R.
    Holmgren, G.
    Holtet, J. A.
    Ivchenko, Nickolay V.
    KTH, Superseded Departments, Alfvén Laboratory.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Khotyaintsev, Y.
    Klimov, S.
    Laakso, H.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory.
    Lybekk, B.
    Marklund, Göran T.
    KTH, Superseded Departments, Alfvén Laboratory.
    Mozer, F.
    Mursula, K.
    Pedersen, A.
    Popielawska, B.
    Savin, S.
    Stasiewicz, K.
    Tanskanen, P.
    Vaivads, A.
    Wahlund, J. E.
    First results of electric field and density observations by Cluster EFW based on initial months of operation2001In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, no 12-okt, p. 1219-1240Article in journal (Refereed)
    Abstract [en]

    Highlights are presented from studies of the electric field data from various regions along the CLUSTER orbit. They all point towards a very high coherence for phenomena recorded on four spacecraft that are separated by a few hundred kilometers for structures over the whole range of apparent frequencies from I mHz to 9 kHz. This presents completely new opportunities to study spatial-temporal plasma phenomena from the magnetosphere out to the solar wind. A new probe environment was constructed for the CLUSTER electric field experiment that now produces data of unprecedented quality. Determination of plasma flow in the solar wind is an example of the capability of the instrument.

  • 63.
    Ivchenko, Nickolay
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Observation of low frequency electromagnetic activity at 1000 km altitude2001In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, p. 643-648Article in journal (Refereed)
    Abstract [en]

    We present a statistical study of low frequency fluctuations of electric and magnetic fields, commonly interpreted as Alfvenic activity. The data base consists of six months of electric and magnetic field measurements by the Astrid-2 microsatellite. The occurrence of the events is studied with respect to the location and general activity. Large regions of broadband Alfvenic activity are persistently observed in the cusp/cleft and, during the periods of high geomagnetic activity, also in the pre-midnight sector of the auroral oval.

  • 64.
    Ivchenko, Nickolay
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Khotyaintsev, Y.
    Inertial Alfven Waves in the Ionosphere: Theoretical Considerations and Experimental Constraints2000In: in Waves in Dusty, Solar and Space Plasmas, ed. F. Verheest, M. Goossens, M. A. Hellberg, and R. Bharuthram, AIP Conf. Proc., Melville, New York, Vol. 537, p. 356-363Article in journal (Refereed)
    Abstract [en]

    Perturbations of electric and magnetic fields with periods of the order of 1 second are commonly observed in the auroral region by satellites and sounding rockets. The events are often accompanied by magnetic field aligned electron precipitation. The observations have been interpreted as inertial Alfvén mode waves. A variety of theories, some of which are surveyed here, have been suggested to describe such events. Recent observations of Alfvénic activity by sounding rockets and satellites are presented and their implications for the theoretical models are discussed.

  • 65.
    Ivchenko, Nickolay
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Lynch, Kristina
    Pietrowski, D.
    Torbert, R.
    Primdahl, F.
    Ranta, A.
    Quasiperiodic oscillations observed at the edge of an auroral arc by Auroral Turbulence 21999In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 26, no 22, p. 3365-3368Article in journal (Refereed)
    Abstract [en]

    The Auroral Turbulence II (AT2) sounding rocket carried three payloads into the auroral ionosphere where they crossed several are structures. At the border of an auroral are a quasiperiodic structure was observed by the magnetic and electric field instruments as well as by the particle detectors. The variations were temporal oscillations, but existed only in a narrow (approximate to 7 km) region transverse to the are, with a correlation length along the are of at least several km. The relation between the electric and magnetic field amplitude indicates the Alfvenic nature of the variations. Field aligned electron precipitation is correlated to the field variations. The narrow band nature of the oscillations and frequency around 0.6 Hz is consistent with waves confined in the ionospheric Alfven resonator.

  • 66.
    Ivchenko, Nickolay V.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran T.
    KTH, Superseded Departments, Alfvén Laboratory.
    Current singularities observed on Astrid-22002In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 30, no 7, p. 1779-1782Article in journal (Refereed)
    Abstract [en]

    Swedish microsatellite Astrid-2 carried out,electric and magnetic field measurements at 1000 km altitude during its operation in January-July, 1999. At a number of occasions sharp gradients in the magnetic field were observed by the satellite. If interpreted as spatial gradients they imply current densities of hundreds muA/m(2). Occurrence of such 11 current singularities is studied. The nature of the events is discussed.

  • 67.
    Johansson, Tommy
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Figueiredo, Sonia
    KTH, Superseded Departments, Alfvén Laboratory.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Fazakerley, Andrew
    Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking.
    Buchert, Stephan
    Swedish Institute of Space Physics, Uppsala.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Intense high-altitude auroral electric fields: temporal and spatial characteristics2004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 7, p. 2485-2495Article in journal (Refereed)
    Abstract [en]

    Cluster electric field, magnetic field, and energetic electron data are analyzed for two events of intense auroral electric field variations, both encountered in the Plasma Sheet Boundary Layer (PSBL), in the evening local time sector, and at approximately 5 R-E geocentric distance. The most intense electric fields (peaking at 450 and 1600 mV/m, respectively) were found to be quasi-static, unipolar, relatively stable on the time scale of at least half a minute, and associated with moving downward FAC sheets (peaking at similar to10 muA/m(2)), downward Poynting flux (peaking at similar to35 mW/m(2)), and upward electron beams with characteristic energies consistent with the perpendicular potentials (all values being mapped to 1 R-E geocentric distance). For these two events in the return current region, quasi-static electric field structures and associated FACs were found to dominate the upward acceleration of electrons, as well as the energy transport between the ionosphere and the magnetosphere, although Alfven waves clearly also contributed to these processes.

  • 68.
    Johansson, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Figueiredo, Sonia
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Buchert, Stephan
    Swedish Institute of Space Physics, Uppsala.
    A statistical study of intense electric fields at 4-7 R-E geocentric distance using Cluster2005In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 7, p. 2579-2588Article in journal (Refereed)
    Abstract [en]

    Intense high-latitude electric fields (> 150 mV/m mapped to ionospheric altitude) at 4-7 R-E geocentric distance have been investigated in a statistical study, using data from the Cluster satellites. The orbit of the Cluster satellites limits the data collection at these altitudes to high latitudes, including the poleward part of the auroral oval. The occurrence and distribution of the selected events have been used to characterize the intense electric fields and to investigate their dependance on parameters such as MLT, CGLat, altitude, and also K-p. Peaks in the local time distribution are found in the evening to morning sectors but also in the noon sector, corresponding to cusp events. The electric field intensities decrease with increasing latitude in the region investigated (above 60 CGLat). A dependence on geomagnetic activity is indicated since the probability of finding an event increases up to K-p=5-6. The scales sizes are in the range up to 10 km (mapped to ionospheric altitude) with a maximum around 4-5 km, consistent with earlier findings at lower altitudes and Cluster event studies. The magnitudes of the electric fields are inversely proportional to the scale sizes. The type of electric field structure (convergent or divergent) is consistent with the FAC direction for a subset of events with electric field intensities in the range 500-1000 mV/m and with clear bipolar signatures. The FAC directions are also consistent with the Region 1 and NBZ current systems, the latter of which prevail only during northward IMF conditions. For scale sizes less than 2 km the majority of the events were divergent electric field structures. Both converging and diverging electric fields were found throughout the investigated altitude range (4-7 RE geocentric distance).

  • 69.
    Johansson, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Liléo, Sonia
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marchaudon, Aurelie
    LPCE, CNRS, Orleans Cedex.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Fazakerley, Andrew
    Mullard Space Science Laboratory, University College, London.
    On the profile of intense high-altitude auroral electric fields at magnetospheric boundaries2006In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, no 6, p. 1713-1723Article in journal (Refereed)
    Abstract [en]

    The profile of intense high-altitude electric fields on auroral field lines has been studied using Cluster data. A total of 41 events with mapped electric field magnitudes in the range between 0.5-1 V/m were examined, 27 of which were co-located with a plasma boundary, defined by gradients in particle flux, plasma density and plasma temperature. Monopolar electric field profiles were observed in 11 and bipolar electric field profiles in 16 of these boundary-associated electric field events. Of the monopolar fields, all but one occurred at the polar cap boundary in the late evening and midnight sectors, and the electric fields were typically directed equatorward, whereas the bipolar fields all occurred at plasma boundaries clearly within the plasma sheet. These results support the prediction by Marklund et al. (2004), that the electric field profile depends on whether plasma populations, able to support intense field-aligned currents and closure by Pedersen currents, exist on both sides, or one side only, of the boundary.

  • 70.
    Johansson, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Liléo, Sonia
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Buchert, Stephan
    Swedish Institute of Space Physics, Uppsala.
    Scale sizes of intense auroral electric fields observed by Cluster2007In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 25, no 11, p. 2413-2425Article in journal (Refereed)
    Abstract [en]

    The scale sizes of intense (>0.15 V/m, mapped to the ionosphere), high-altitude (4-7 R-E geocentric distance) auroral electric fields (measured by the Cluster EFW instrument) have been determined in a statistical study. Monopolar and bipolar electric fields, and converging and diverging events, are separated. The relations between the scale size, the intensity and the potential variation are investigated.

    The electric field scale sizes are further compared with the scale sizes and widths of the associated field-aligned currents (FACs). The influence of, or relation between, other parameters (proton gyroradius, plasma density gradients, and geomagnetic activity), and the electric field scale sizes are considered.

    The median scale sizes of these auroral electric field structures are found to be similar to the median scale sizes of the associated FACs and the density gradients (all in the range 4.2-.9 km) but not to the median proton gyroradius or the proton inertial scale length at these times and locations (22-30km). (The scales are mapped to the ionospheric altitude for reference.)

    The electric field scale sizes during summer months and high geomagnetic activity (K-p>3) are typically 2-3 km, smaller than the typical 4-5 km scale sizes during winter months and low geomagnetic activity (K-p <= 3), indicating a dependence on ionospheric conductivity.

  • 71.
    Karlsson, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    A statistical study of intense low-altitude electric fields observed by Freja1996In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 23, p. 1005-1008Article in journal (Refereed)
    Abstract [en]

    Extremely intense (up to 2 V/m) and fine-structured (1–5 km) electric fields have been observed by the Freja satellite at altitudes of 1400–1770 km. To study the occurrence and characteristics of these intense electric field events, a database was set up by searching 7 months' worth of Freja data for events with peak values greater than 200 mV/m. The intense electric field events are distributed over all local times, but they are mostly concentrated to the midnight and early morning sector of the auroral oval. The events are seen to be associated with low ambient ionospheric conductivities, but are not activity dependent. The most intense events (located in the midnight sector) are associated with the smallest scale sizes, whereas the less intense events on the day side have larger scale sizes.

    The findings are consistent with the interpretation that a majority of the intense electric field events observed by Freja are associated with the small-scale, east-west-aligned, low-conductivity bands devoid of auroral emissions, known as black auroral bands, or with the curls that may develop when these bands go unstable. Several observations of diverging electric fields of around 1 V/m at 800 km altitude, within the southern auroral oval, may serve as support for the prediction that intense electric fields should exist also at ionospheric altitudes.

  • 72.
    Karlsson, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Results from the DC Electric Field Experiment on the Freja Satellite1999In: Advances in Space Research, Vol. 23, p. 1657-1665Article in journal (Refereed)
  • 73.
    Karlsson, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Simulations of effects of small-scale auroral current closure in the return current region1998In: Physics of space plasmas, Vol. 15, p. 401-Article in journal (Other academic)
  • 74.
    Karlsson, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Malkki, A
    Subauroral electric fields observed by the Freja satellite: A statistical study1998In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0233, Vol. 103, no A3, p. 4327-4341Article in journal (Refereed)
    Abstract [en]

    Over 12 months of Freja electric field data have been scanned for subauroral electric fields (SAEF) to enable a comprehensive study of the ionospheric signatures of such electric fields. SAEF are encountered from 1800 to 0200 MLT in agreement with an earlier study. However, a large majority of the SAEF are encountered at a time slightly premidnight (2200 - 2300 MLT), with rather few occurrences before 2000 MLT and after 2400 MLT. Furthermore, the strength of the subauroral electric field is generally much larger for events close to 2200 MLT than for other events. The data confirm that SAEF occur during the substorm recovery phase but also show that SAEF occur earlier during recovery when located close to 2200 MLT than at other local times. The dependence on season and geomagnetic activity is studied, and it is found that the SAEF are more commonly observed at times of high activity when the subauroral electric fields are also generally stronger, except close to winter solstice, when strong electric fields are observed during low activity. The potentials associated with the SAEF and the relation to interplanetary magnetic field B-y are also studied. The observations are discussed in context with substorm-related field-aligned currents and the midlatitude trough, and we present evidence that support and refine one of the proposed production mechanisms.

  • 75.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Brenning, Nils
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Axnäs, Ingvar
    On enhanced aurora and low-altitude parallel electric fields2005In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, no 5, p. 419-422Article in journal (Refereed)
    Abstract [en]

    Enhanced auroras are bands of enhanced intensity, sometimes observed along the bottom edges of auroral arcs. It is here proposed that they sometimes are due to local electron energization by low-altitude. downward-directed DC electric fields. which arise as a consequence of the ionospheric response to small-scale auroral current systems. Simulations of such structures are presented. and the electron energization mechanism is discussed. The enhanced auroras would, in this model, appear parallel and close to (perhaps only a few kin front) an ordinary auroral arc. Detailcd 3-D observations of auroral arc structures could resolve if enhanced auroras sometimes take this form.

  • 76.
    Karlsson, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran T.
    KTH, Superseded Departments, Alfvén Laboratory.
    Figueiredo, Sonia
    KTH, Superseded Departments, Alfvén Laboratory.
    Johansson, Tommy
    KTH, Superseded Departments, Alfvén Laboratory.
    Buchert, S.
    Separating spatial and temporal variations in auroral electric and magnetic fields by Cluster multipoint measurements2004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 7, p. 2463-2472Article in journal (Refereed)
    Abstract [en]

    Cluster multipoint measurements of the electric and magnetic fields from a crossing of auroral field lines at an attitude of 4 R-E are used to show that it is possible to resolve the ambiguity of temporal versus spatial variations in the fields. We show that the largest electric fields (of the order of 300 mV/m when mapped down to the ionosphere) are of a quasi-static nature, unipolar, associated with upward electron beams, stable on a time scale of at least half a minute, and located in two regions of downward current. We conclude that they are the high-altitude analogues of the intense return current/black auroral electric field structures observed at lower altitudes by Freja and FAST. In between these structures there are temporal fluctuations, which are shown to likely be downward travelling Alfven waves. The periods of these waves are 20-40 s, which is not consistent with periods associated with either the Alfvenic ionospheric resonator, typical field line resonances or substorm onset related Pi2 oscillations. The multipoint measurements enable us to estimate a lower limit to the perpendicular wavelength of the Alfven waves to be of the order of 120 kin, which suggests that the perpendicular wavelength is similar to the dimension of the region between the two quasi-static structures. This might indicate that the Alfven waves are ducted within a wave guide, where the quasi-static structures are associated with the gradients making up this waveguide.

  • 77.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Plaschke, Ferdinand
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Hietala, Heli
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, 603 Charles E Young Dr East,Slichter Hall 6844D, Los Angeles, CA 90095 USA..
    Archer, Martin
    Queen Mary Univ London, Sch Phys & Astron, London E1 4NS, England..
    Blanco-Cano, Xochitl
    Univ Nacl Autonoma Mexico, Inst Geofis, Ciudad Univ, Cdmx, Mexico..
    Kajdic, Primoz
    Univ Nacl Autonoma Mexico, Inst Geofis, Ciudad Univ, Cdmx, Mexico..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Investigating the anatomy of magnetosheath jets - MMS observations2018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 36, no 2, p. 655-677Article in journal (Refereed)
    Abstract [en]

    We use Magnetosphere Multiscale (MMS) mission data to investigate a small number of magnetosheath jets, which are localized and transient increases in dynamic pressure, typically due to a combined increase in plasma velocity and density. For two approximately hour-long intervals in November, 2015 we found six jets, which are of two distinct types. (a) Two of the jets are associated with the magnetic field discontinuities at the boundary between the quasi-parallel and quasi-perpendicular magnetosheath. Straddling the boundary, the leading part of these jets contains an ion population similar to the quasi-parallel magnetosheath, while the trailing part contains ion populations similar to the quasi-perpendicular magnetosheath. Both populations are, however, cooler than the surrounding ion populations. These two jets also have clear increases in plasma density and magnetic field strength, correlated with a velocity increase. (b) Three of the jets are found embedded within the quasi-parallel magnetosheath. They contain ion populations similar to the surrounding quasi-parallel magnetosheath, but with a lower temperature. Out of these three jets, two have a simple structure. For these two jets, the increases in density and magnetic field strength are correlated with the dynamic pressure increases. The other jet has a more complicated structure, and no clear correlations between density, magnetic field strength and dynamic pressure. This jet has likely interacted with the magnetosphere, and contains ions similar to the jets inside the quasi-parallel magnetosheath, but shows signs of adiabatic heating. All jets are associated with emissions of whistler, lower hybrid, and broadband electrostatic waves, as well as approximately 10 s period electromagnetic waves with a compressional component. The latter have a Poynting flux of up to 40 mu Wm(-2) and may be energetically important for the evolution of the jets, depending on the wave excitation mechanism. Only one of the jets is likely to have modified the surrounding magnetic field into a stretched configuration, as has recently been reported in other studies. None of the jets are associated with clear signatures of either magnetic or thermal pressure gradient forces acting on them. The different properties of the two types also point to different generation mechanisms, which are discussed here. Their different properties and origins suggest that the two types of jets need to be separated in future statistical and simulation studies.

  • 78. Khotyaintsev, Y V
    et al.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Burch, J. L.
    et al.,
    Electron jet of asymmetric reconnection2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 11, p. 5571-5580Article in journal (Refereed)
    Abstract [en]

    We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E-vertical bar amplitudes reaching up to 300mVm(-1) and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

  • 79. KLETZING, CA
    et al.
    PASCHMANN, G
    BOEHM, MH
    HAERENDEL, G
    SCKOPKE, N
    BAUMJOHANN, W
    TORBERT, RB
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    ELECTRIC-FIELDS DERIVED FROM ELECTRON-DRIFT MEASUREMENTS1994In: GEOPHYSICAL RESEARCH LETTERS, ISSN 0094-8276, Vol. 21, no 17, p. 1863-1866Article in journal (Refereed)
    Abstract [en]

    The first observations of electric fields derived from electron E x B drift measurements aboard the Freja spacecraft are presented. The instrument injects a weak beam of 3 keV electrons and measures the displacement of the returning electrons after one gyroperiod. After removing effects due to beam-detector geometry and applying an empirical calibration based upon comparison with the computed v x B electric field induced by the spacecraft motion, good agreement is found when the electron drift measurements are compared with the electric field components measured by the double probe experiment. Examples are presented in which moderately large electric fields are observed near the edges of or adjacent to electron precipitation regions with little or no electric field within.

  • 80. Le Contel, O.
    et al.
    Retino, A.
    Breuillard, H.
    Mirioni, L.
    Robert, P.
    Chasapis, A.
    Lavraud, B.
    Chust, T.
    Rezeau, L.
    Wilder, F. D.
    Graham, D. B.
    Argall, M. R.
    Gershman, D. J.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Khotyaintsev, Y. V.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ergun, R. E.
    Goodrich, K. A.
    Burch, J. L.
    Torbert, R. B.
    Needell, J.
    Chutter, M.
    Rau, D.
    Dors, I.
    Russell, C. T.
    Magnes, W.
    Strangeway, R. J.
    Bromund, K. R.
    Leinweber, H. K.
    Plaschke, F.
    Fischer, D.
    Anderson, B. J.
    Le, G.
    Moore, T. E.
    Pollock, C. J.
    Giles, B. L.
    Dorelli, J. C.
    Avanov, L.
    Saito, Y.
    Whistler mode waves and Hall fields detected by MMS during a dayside magnetopause crossing2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 12, p. 5943-5952Article in journal (Refereed)
    Abstract [en]

    We present Magnetospheric Multiscale (MMS) mission measurements during a full magnetopause crossing associated with an enhanced southward ion flow. A quasi-steady magnetospheric whistler mode wave emission propagating toward the reconnection region with quasi-parallel and oblique wave angles is detected just before the opening of the magnetic field lines and the detection of escaping energetic electrons. Its source is likely the perpendicular temperature anisotropy of magnetospheric energetic electrons. In this region, perpendicular and parallel currents as well as the Hall electric field are calculated and found to be consistent with the decoupling of ions from the magnetic field and the crossing of a magnetospheric separatrix region. On the magnetosheath side, Hall electric fields are found smaller as the density is larger but still consistent with the decoupling of ions. Intense quasi-parallel whistler wave emissions are detected propagating both toward and away from the reconnection region in association with a perpendicular anisotropy of the high-energy part of the magnetosheath electron population and a strong perpendicular current, which suggests that in addition to the electron diffusion region, magnetosheath separatrices could be a source region for whistler waves.

  • 81.
    Li, Bin
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Alm, Love
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Masson, Arnaud
    Statistical altitude distribution of Cluster auroral electric fields, indicating mainly quasi-static acceleration below 2.8 R-E and Alfvenic above2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 11, p. 8984-8991Article in journal (Refereed)
    Abstract [en]

    Results are presented from a statistical study of high-altitude electric fields and plasma densities using Cluster satellite data collected during 9.5years between 2 and 4 R-E. The average electric fields are most intense on the nightside and associated with an extensive plasma density cavity, with densities of 1cm(-3) or less. The intense electric fields are concentrated in two regions, separated by an altitude gap at about 2.8 R-E. Below this, the average electric field magnitudes reach about 50mV/m (mapped to the ionosphere) between 22 and 01 magnetic local time (MLT). Above 3 R-E, the fields are about twice as high and spread over a broader MLT range. These fields occur in a region where the (E/B)/V-A ratio is close to unity, which suggests an Alfvenic origin. The intense low-altitude electric fields are interpreted to be quasi-static, associated with the auroral acceleration region. This is supported by their location in MLT and altitude, and by a (E/B)/V-A ratio much below unity. The local electric field minimum between the two regions indicates a partial closure of the electrostatic potentials in the lower region. These results show similarities with model results of reflected Alfven waves by Lysak and Dum (1983), and with the O-shaped potential model, with associated wave-particle interaction at its top, proposed by Janhunen et al. (2000).

  • 82.
    Li, Bin
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sadeghi, Soheil
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Vaivads, Andris
    Fazakerley, Andrew
    Zhang, Yongliang
    Lucek, Elizabeth
    Sergienko, Tima
    Nilsson, Hans
    Masson, Arnaud
    Inverted-V and low-energy broadband electron acceleration features of multiple auroras within a large-scale surge2013In: Journal of Geophysical Research: Space Physics, ISSN 2169-9380, Vol. 118, no 9, p. 5543-5552Article in journal (Refereed)
    Abstract [en]

    Results are presented from a Cluster C2 satellite crossing through the acceleration region of multiple auroral structures within a large-scale surge, simultaneously monitored by DMSP F17 imager data. The magnetic and electric field data are consistent with the auroral distribution at large and medium scales. We identify the quasi-static acceleration above and below C2 orbit by downgoing inverted-V electrons and parallel electric potential drops, respectively. In the poleward surge region, within or adjacent to the inverted-V arcs, intense low-energy (broadband) electron fluxes are seen as well as a rough equality between E/B and the Alfven velocity, suggesting that these are of Alfvenic origin. The most poleward and equatorward auroral structure is found to be Alfvenic and quasi-static, respectively. In between, the structures are of mixed origin. We estimate the relative role of the acceleration processes by the contributions to the downward electron energy flux by electrons above and below 1.62keV. Although these are local estimates, they should be representative also below Cluster altitude, except for two regions of intense downward Poynting flux, the power of which will be dissipated at lower altitudes and increasing the Alfvenic contribution. This is also supported by intense fluxes of low-energy, broadband, upgoing electrons observed within these regions. Otherwise, the inverted-V contribution dominates for most of the auroral structures observed by Cluster. The Alfvenic contribution to the mixed arc emissions is to extend these to higher altitudes, as shown by numerical simulation results.

  • 83.
    Lileo, Sonia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Statistical study on the occurrence of ASAID electric fields2010In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, no 2, p. 439-448Article in journal (Refereed)
    Abstract [en]

    The first statistical results on the occurrence of abnormal subauroral ion drifts (ASAID) are presented based on electric and magnetic field measurements from the low-altitude Astrid-2 satellite. ASAID are narrow regions of rapid eastward ion drifts observed in the subauroral ionosphere. They correspond to equatorward-directed electric fields with peak amplitudes seen to vary between 45 mV/m and 185 mV/m, and with latitudinal extensions between 0.2 degrees and 1.2 degrees Corrected Geomagnetic Latitude (CGLat), reaching in some cases up to 3.0 degrees CGLat. Opposite to subauroral ion drifts (SAID) that are known to be substorm-related, ASAID are seen to occur predominantly during extended periods of low substorm activity. Our results show that ASAID are located in the vicinity of the equatorward edge of the auroral oval, mainly in the postmidnight sector between 23:00 and 03:00 magnetic local time. They are associated with a local current system with the same scale-size as the corresponding ASAID, composed by a region of downward field-aligned currents (FACs) flowing in the ASAID poleward side, and a region of upward flowing FACs in the equatorward side. The FACs have densities between 0.5 and 2.0 mu A/m(2). The data suggest that ASAID do not contribute significantly to the reduction of the ionospheric conductivity. ASAID are seen to have life times of at least 3.5 h. A discussion on possible mechanisms for the generation of ASAID is presented. We speculate that the proximity of the electron to the ion plasma sheet inner boundaries and of the plasmapause to the ring current outer edge, during extended quiet times, is an important key for the understanding of the generation of ASAID electric fields.

  • 84.
    Liléo, Sonia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Johansson, Tommy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Magnetosphere-ionosphere coupling during periods of extended high auroral activity: A case study2008In: Annales Geophysicae, ISSN 0992-7689, Vol. 26, p. 583-591Article in journal (Refereed)
    Abstract [en]

    Results are presented from a case study of a plasma boundary crossing by the Cluster spacecraft during an extended period of high auroral activity. The boundary between the magnetotail lobe region of the Southern Hemisphere and the plasma sheet boundary layer, was characterized by intense electric and magnetic field variations, structured upward accelerated ion beams, narrow-scale large field-aligned Poynting fluxes directed upward away from the ionosphere, and a relatively sharp plasma density gradient. The observations are shown to be consistent with the concept of a multi-layered boundary with temporal and/or spatial variations in the different layers. H+ and O+ ion beams are seen to be accelerated upwards both by means of a field-aligned electric field and by magnetic pumping caused by large-amplitude and low-frequency electric field fluctuations. The peak energy of the ion beams may here be used as a diagnostic tool for the temporal evolution of the spatial structures, since the temporal changes occur on a time-scale shorter than the times-of-flight of the detected ion species. The case study also shows the boundary region to be mainly characterized by a coupling of the detected potential structures to the low ionosphere during the extended period of high auroral activity, as indicated by the intense field-aligned Poynting fluxes directed upward away from the ionosphere.

  • 85.
    Lindqvist, Per-Arne
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory.
    Nilsson, B. H.
    KTH, Superseded Departments, Alfvén Laboratory.
    Bylander, Lars
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    The double probe electric field experiment on Freja: Telemetry format description1994Report (Other academic)
  • 86.
    Lindqvist, Per-Arne
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory.
    Plasma Characteristics Determined by the Freja Electric Field Instrument1994Report (Other academic)
  • 87.
    Lindqvist, Per-Arne
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Plasma characteristics determined by the Freja electric field instrument1994In: Space Science Reviews, ISSN 00386308 (ISSN), Vol. 70, no 3-4, p. 593-602Article in journal (Refereed)
    Abstract [en]

    A new approach to the study of ionospheric plasma characteristics is presented using data from the Freja double probe electric field instrument. Plasma characteristics are derived from continuous measurements of the satellite potential and from intermittent Langmuir sweeps. These provide information on both relative variations in the plasma density and absolute density and temperature, useful for comparisons with other plasma measurements on Freja, and essential for the interpretation of the electric field measurements. The on-board memory makes it possible to obtain full-orbit coverage of this type of information, which is a new feature of the Freja measurements. The memory is also used for high time resolution Langmuir sweeps which allow for the first time detailed studies of the time behavior of the probe response and computation of the probe-plasma capacitance. Comparisons are also made with similar measurements on earlier missions. © 1994 Kluwer Academic Publishers.

  • 88.
    Lindqvist, Per-Arne
    et al.
    KTH, Superseded Departments, Physics.
    Marklund, Göran T.
    KTH, Superseded Departments, Physics.
    A STATISTICAL STUDY OF HIGH-ALTITUDE ELECTRIC-FIELDS MEASURED ON THE VIKING SATELLITE1990In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 95, no A5, p. 5867-5876Article in journal (Refereed)
  • 89. Lynch, A.
    et al.
    Pietrowski, D.
    Torbert, B.
    Ivchenko, Nickolay
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Primdahl, F.
    Multiple-point electron measurements in a nightside auroral arc: Auroral Turbulence II particle observations1999In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 26, no 22, p. 3361-3364Article in journal (Refereed)
    Abstract [en]

    We report here three-point measurements of bursty, velocity-dispersed, field-aligned electron precipitation at the poleward edge of a northward-moving, post-breakup, nightside auroral arc. The three-point measurement allows detection of the proper motion of the inverted-V arc, which is shown to be 550 m/sec northward. The velocity dispersion patterns are fitted to find the source altitude of the precipitation bursts as a function of distance from the poleward edge of the are. These source points are interpreted to trace out the low-altitude boundary of the inverted-V potential drop, which is seen to rise both in time, and in the northward direction. The precipitation bursts under the inverted-V are seen to have an are-aligned velocity which varies with time, and which is consistent with the measured E x B local drift speed.

  • 90.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Auroras Negras2003In: Investigacion y Ciencia, ISSN 0210-136X, Vol. No. 322, p. 44-49Article in journal (Other (popular science, discussion, etc.))
  • 91.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    André, Mats
    KTH, Superseded Departments, Alfvén Laboratory.
    Lundin, Rickard
    KTH, Superseded Departments, Alfvén Laboratory.
    Swedish small satellites investigate the aurora2004In: EOS: Transactions, ISSN 0096-3941, E-ISSN 2324-9250, Vol. 85, no 16, p. 157+164-165Article in journal (Refereed)
  • 92.
    Marklund, Göran
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Block, Lars
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Rocket measurements of electric fields, electron density and temperature during different phases of auroral substorms1981In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 29, no 2, p. 249-259Article in journal (Refereed)
    Abstract [en]

    On 27 January 1979, three rocket payloads were launched from Kiruna, Sweden into different phases of two successive auroral substorrns. Among other experiments, the payloads carried the RIT double probe electric field experiments providing electric field, electron density and temperature data which are presented here. These data supported by rocket particle observations are discussed mainly in association with ground-based observations (magnetometer, TV) and very briefly with GEOS electric field data. The motions of the auroral forms as obtained from auroral pictures are compared with E × B/B2 drifts and the currents calculated from the rocket electric field and density measurements with the equivalent current system deduced from ground-based magnetometer data (Scandinavian Magnetometer Array).

  • 93.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    On the influence of localized electric fields and field-aligned currents associated with polar arcs on the global potential distribution1991In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 96, no A8, p. 13977-13983Article in journal (Refereed)
    Abstract [en]

    The influence of localized field-aligned current, associated with intense transpolar arcs mostly occuring during periods of northward interplanetary magnetic field (IMF), on the global electrodynamics has been investigated using a numerical simulation model. Idealized field-aligned current distributions representing both the region 1/2 system of the auroral oval and the transpolar arc as well as a corresponding ionospheric conductivity distribution are fed into the model to calculate the potential distributions. The transpolar arc has been represented by a few alternative field-aligned current distributions which are different in the way the downward return currents are distributed in the ionosphere. For the case with a single, upward current sheet the potential pattern assumes a form similar to that typical for IMF B(y) positive conditions, namely a large dusk cell with sunward drift reaching very high latitudes and a crescent-shaped dawn cell. If the conductivity of the main auroral oval is comparable to that of the polar arc the dusk cell will have two local potential minima and thus a region of weak antisunward convection in between. For the cases with two equal but oppositely directed current sheets the potential patterns are very similar to the symmetrical two-cell reference pattern associated with solely the region 1/2 system with an exception for the immediate vicinity of the theta aurora. Depending on the direction of the polar arc current sheets the dawn-dusk electric field will either be reversed (or weakened) or intensified at the location of the transpolar arc. The presence of a reversal depend, however, not only on the relative magnitude between the polar arc currents and those of the region 1/2 system but also on the characteristics of the acceleration region and of the conductivity distribution associated with the polar arc. Comparisons are made between the model results and Viking electric field data for a number of polar arc crossings to reveal the most common electrodynamical signatures of these auroral phenomena.

  • 94.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Toward a better understanding of the global auroral electrodynamics through numerical modeling studies1991In: Magnetospheric Substorms, Washington, DC: American Geophysical Union (AGU), 1991, p. 305-319Chapter in book (Refereed)
    Abstract [en]

    Results from numerical model studies are presented focusing on various aspects of the auroral electrodynamics. Studies of specific events, by means of extensive sets of observations which are fed into a numerical model to provide snapshots of the global electrodynamics, have been conducted in parallel with theoretical model studies. This has proven to be an efficient way to obtain a better physical understanding of the events in general and of the interrelationships between the physical parameters in particular. Of special interest are the electrodynamical features of northward IMF phenomena, to which we pay particular attention in this review. Examples are presented of transpolar arc events with particular emphasis on the convection signatures and how these relate to the auroral distribution. The influence on the global potential distribution of localized Birkeland currents associated with transpolar arcs is shown to be quite different from that of the more extended large-scale NBZ currents. For the former case the potential pattern is typically of a two cell type with modifications showing up as a poleward expansion of one of the cells, a local electric field reversal or possibly an electric field reduction at the center of the arc depending on how the arc-associated currents close in the ionosphere. For the case with large-scale NBZ currents, presumably related to extended regions of dim auroral features, the potential pattern is shown to have two, three, or four large-scale cells depending on the ratio between the NBZ and the oval currents, on the sign of the IMF By, and on the ionospheric conductivity.Of importance to these studies are also the statistical properties of the global electric field, current, and conductivity distributions and the relation between these for various conditions, a subject that will be briefly discussed. The effect of parallel potential drops in regions of upward field-aligned current has been taken into account in the model by assuming a linear relationship between these. Distortions of the equipotential contours above the potential drop occur as a result of this assumption as illustrated by projecting the ionospheric potential to the magnetosphere.

  • 95.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bylander, L.
    KTH, Superseded Departments, Alfvén Laboratory.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Astrid 2, A low-budget microsatellite mission for auroral research1997In: European Space Agency, (Special Publication) ESA SP, ISSN 03796566 (ISSN), no 397, p. 387-394Article in journal (Refereed)
    Abstract [en]

    The next in the Astrid series of low-budget microsatellite missions will be devoted to classical auroral research. The challenge of this mission is to demonstrate the possibility to carry out comprehensive auroral investigations on a microsatellite platform having the size 0.45 × 0.45 × 0.3 m at a cost of about 2 MUSD. A successful mission will open up new less expensive ways carrying out auroral research in the future, ways which are complementary to the more ambitious programmes run within ESA and NASA. Of particular interest are multipoint measurements within the auroral acceleration region using clusters of microsatellites. New light-weight and compact instruments and deployment systems have been developed for the Astrid-2 mission. The payload will carry an integrated electric and magnetic field instrument, including a Langmuir probe, a lightweight ion and electron spectrometer, and two spin-scanning UV photometers for Lyman α and oxygen emissions in the aurora. The electric field probes will be deployed using a newly developed light-weight system for wire boom deployment. Other novel features to be used on Astrid-2 are data compression and data filtering. Astrid-2 is to be launched on a Kosmos vehicle from Plesetsk in 1997 into an 83° inclination circular orbit at 1000 km altitude. The mission will use a geographically distributed ground station network for high-speed S-band data reception, one station to be located at Solna, Sweden and another at the South African Antarctic base SANAE.

  • 96.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Falthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    On intense diverging electric fields associated with black aurora1994In: Geophysical Research Letters, ISSN 00948276 (ISSN), Vol. 21, no 17, p. 1859-1862Article in journal (Refereed)
    Abstract [en]

    Results are presented from the double-probe electric field instrument on the Freja satellite with particular focus on the fine-structured and dynamic plasma of the upper auroral ionosphere. The high-resolution measurements show frequently occuring intense and irregular fine-scale electric fields similar to those observed at higher altitudes by, for example, the S3-3 and Viking satellites. Whereas the high-altitude fields tend to be directly related to the auroral fine-structure this is not always the case for the low-altitude fields as illustrated by high-resolution data of a pair of very intense (≈ 1 V/m), narrow electric field structures in the post-midnight sector in the large-scale downward field-aligned current region. The structures are found to be associated with an excess of positive space charge (diverging electric fields), dropouts of precipitating electrons as well as depletions of thermal plasma, and significant wave activity. Combined with the scale-size of the structures (≈ 1 km) and the spacing between them (≈ 5 km) these observations suggest that the intense electric fields are related to east-west aligned vortex street structures of black aurora, similar to auroral curls but with opposite sense of rotation (clockwise seen antiparallel to B) and a total absence of auroral emissions. The detection of these structures was made possible by the relatively low inclination of the Freja orbit, which at times is almost tangential to the auroral oval. Thus, the Freja orbit provides a new perspective for studying many nightside auroral phenomena both at smaller scales (vortices) and at larger scales as exemplified by observations of north-south oriented auroral structures caused by rotational arc distortions.

  • 97.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    ERLANDSON, RE
    POTEMRA, TA
    Signatures of the high-altitude polar cusp and dayside auroral regions as seen by the Viking electric-field experiment1990In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 95, no A5, p. 5767-5780Article in journal (Refereed)
  • 98.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    ELIASSON, L
    On the occurrence and characteristics of intense low-altitude electric fields observed by Freja1995In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 13, p. 704-712Article in journal (Refereed)
    Abstract [en]

    High-resolution measurements by the double probe electric field instrument on the Freja satellite are presented. The observations show that extremely intense (up to 1 V m-1) and fine-structured (< 1 km) electric fields exist at auroral latitudes within the altitude regime explored by Freja (up to 1700 km). The intense field events typically occur within the early morning sector of the auroral oval (01-07 MLT) during times of geomagnetic activity. In contrast to the observations within the auroral acceleration region characterized by intense converging electric fields associated with electron precipitation, upward ion beams and upward field-aligned currents, the intense electric fields observed by Freja are often found to be diverging and located within regions of downward field-aligned currents outside the electron aurora. Moreover, the intense fields are observed in conjunction with precipitating and transversely energized ions of energies 0.5-1 keV and may play an important role in the ion heating. The observations suggest that the intense electric field events are associated with small-scale low-conductivity ionospheric regions void of auroral emissions such as east-west aligned dark filaments or vortex streets of black auroral curls located between or adjacent to auroral arcs within the morningside diffuse auroral region. We suggest that these intense fields also exist at ionospheric altitudes although no such observations have yet been made. This is possible since the height-integrated conductivity associated with the dark filaments may be as low as 0.1 S or less. In addition, Freja electric field data collected outside the auroral region are discussed with particular emphasis on subauroral electric fields which are observed within the 19-01 MLT sector between the equatorward edge of the auroral oval and the inner edge of the ring current.

  • 99.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hardy, D. A.
    Rich, F. J.
    Instantaneous pictures of the high-latitude electrodynamics using Viking and DMSP/F7 observations1987In: European Rocket & Balloon Programmes and Related Research, 1987, Vol. 270, p. 45-50Conference paper (Other academic)
  • 100.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Investigation of fine-scale aurora with the Freja electric field instrument1992In: Study of the Solar-Terrestrial System, 1992, Vol. 346, p. 307-313Conference paper (Other academic)
1234 51 - 100 of 152
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