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  • 51. Erlandson, R. E.
    et al.
    Zanetti, L. J.
    Acuna, M. H.
    Eriksson, A. I.
    Eliasson, L.
    Boehm, M. H.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Freja observations of electromagnetic ion cyclotron ELF waves and transverse oxygen ion acceleration on auroral field lines1994In: Geophysical Research Letters, ISSN 00948276 (ISSN), Vol. 21, no 17, p. 1855-1858Article in journal (Refereed)
    Abstract [en]

    Extremely low-frequency (ELF) magnetic and electric field plasma wave emissions were recorded on 2 October 1993 on auroral field lines by the Magnetic Field Experiment during Freja orbit 4770. The ELF wave frequencies were below the local oxygen gyrofrequency (25 Hz) and between the helium and proton gyrofrequencies (100 to 400 Hz). The ELF waves, interpreted as electromagnetic ion cyclotron (EMIC) waves, were observed in a region of inverted-v-type electron precipitation. The EMIC waves were correlated over time with auroral and lower energy (≈ 100 eV) electrons, which are both possible sources of free energy, and also with transversely accelerated oxygen ions. The waves above the helium gyrofrequency were more closely correlated with the transverse oxygen ion acceleration than the waves below the oxygen gyrofrequency. These observations are consistent with a scenario in which electron beams generate EMIC waves, which then produce transverse oxygen ion acceleration through a gyroresonant interaction.

  • 52. Feldstein, Y I
    et al.
    Gromova, L I
    Levitin, A E
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory.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    KTH, Superseded Departments, Alfvén Laboratory.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.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Electromagnetic characteristics of the high-latitude ionosphere during the various phases of magnetic substorms1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A9, p. 19921-19936Article in journal (Refereed)
    Abstract [en]

    Model calculations of the electrodynamics of the high-latitude ionosphere are compared to measurements made by the Viking satellite during July-August 1986. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field. The events chosen correspond to the growth, the expansion, and the recovery phases of substorms. During the growth and expansion phases the correlation between the model results and the satellite data is rather good. During recovery phase the correlation is not as good. The correlation between modeled and observed quantities suggest that during growth and expansion phase the magnetosphere is mainly directly driven by the solar wind, whereas during recovery phase it is mainly driven by internal processes, i.e., loading-unloading. Best fit is obtained when averaging the measured quantities over a few minutes, which means adjusting the spatial resolution of the measurements to the resolution of the model. Different time delays between the interplanetary magnetic field observations and those of Viking were examined. Best agreement was obtained, not surprisingly, for time delays corresponding to the estimated information transit time from the solar wind spacecraft to the ionosphere.

  • 53.
    Feldstein, Y. I.
    et al.
    IZMIRIAN, Troitsk, Russia.
    Gromova, L. I.
    IZMIRIAN, Troitsk, Russia.
    Levitin, A. E.
    IZMIRIAN, Troitsk, Russia.
    Blomberg, Lars
    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.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    To directly driven and loading-unloading processes during substorm1996In: European Space Agency, (Special Publication) ESA SP, ISSN 03796566 (ISSN), no 389, p. 69-74Article in journal (Refereed)
    Abstract [en]

    Model calculations of the electric fields in the high-latitude ionosphere are compared to measurements made by the Viking satellite during August 3, 1986 pass. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field (IMF). The event chosen correspond to the growth phase of substorm. The correlation between the model results and the satellite data is high, which assumes directly driven of the magnetosphere by the solar wind. Similar high correlation exists between the electric field in the solar wind (V*Bs) and AL magnetic activity indices, if time delays between the V*Bs observations in space and magnetic activity above the Earth's ground are taken into account. It is concluded, that the directly driven response of the magnetosphere to highly variable solar wind electric field is the main feature of geomagnetic activity at high latitudes.

  • 54.
    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.

  • 55. Feldstein, Y. I.
    et al.
    Popov, V. A.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Prigancova, A.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kozyra, J. U.
    Tsurutani, B. T.
    Gromova, L. I.
    Levitin, A. E.
    Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals2006In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 24, no 8, p. 2243-2276Article in journal (Refereed)
    Abstract [en]

    We investigate variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. Special attention was paid to the complex structure of the electrojets and their interrelationship with diffuse and discrete particle precipitation and field-aligned currents in the dusk sector. During magnetospheric substorms the eastward electrojet (EE) location in the evening sector changes with local time from cusp latitudes (Phi similar to 77 degrees) during early afternoon to latitudes of diffuse auroral precipitation (Phi similar to 65 degrees) equatorward of the auroral oval before midnight. During the main phase of an intense magnetic storm the eastward currents in the noon-early evening sector adjoin to the cusp at Phi similar to 65 degrees and in the pre-midnight sector are located at subauroral latitude Phi similar to 57 degrees. The westward electrojet (WE) is located along the auroral oval from evening through night to the morning sector and adjoins to the polar electrojet (PE) located at cusp latitudes in the day-side sector. The integrated values of the eastward (westward) equivalent ionospheric current during the intense substorm are similar to 0.5 MA (similar to 1.5 MA), whereas they are 0.7 MA (3.0 MA) during the storm main phase maximum. The latitudes of auroral particle precipitation in the dusk sector are identical with those of both electrojets. The EE in the evening sector is accompanied by particle precipitation mainly from the Alfven layer but also from the near-Earth part of the central plasma sheet. In the lower-latitude part of the EE the field-aligned currents (FACs) flow into the ionosphere (Region 2 FAC), and at its higher-latitude part the FACs flow out of the ionosphere (Region 1 FAC). During intense disturbances, in addition to the Region 2 FAC and the Region 1 FAC, a Region 3 FAC with the downward current was identified. This FAC is accompanied by diffuse electron precipitation from the plasma sheet boundary layer. Actually, the triple system of FAC is observed in the evening sector and, as a consequence, the WE and the EE overlap. The WE in the evening sector comprises only the high-latitude periphery of the plasma precipitation region and corresponds to the Hall current between the Region 1 FAC and Region 3 FAC. During the September 1998 magnetic storm, two velocity bursts (similar to 2-4 km/s) in the magnetospheric convection were observed at the latitudes of particle precipitation from the central plasma sheet and at subauroral latitudes near the ionospheric trough. These kind of bursts are known as subauroral polarization streams (SAPS). In the evening sector the Alfven layer equatorial boundary for precipitating ions is located more equatorward than that for electrons. This may favour northward electric field generation between these boundaries and may cause high speed westward ions drift visualized as SAPS. Meanwhile, high speed ion drifts cover a wider range of latitudes than the distance between the equatorward boundaries of ions and electrons precipitation. To summarize the results obtained a new scheme of 3-D currents in the magnetosphere-ionosphere system and a clarified view of interrelated 3-D currents and magnetospheric plasma domains are proposed.

  • 56.
    Feldstein, Y. I.
    et al.
    IZMIRAN, Troitsk, Russia.
    Popov, V. A.
    IZMIRAN, Troitsk, Russia.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Prigancova, A.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kozyra, J. U.
    Tsurutani, B. T.
    Gromova, L. I.
    IZMIRAN, Troitsk, Russia.
    Levitin, A. E.
    IZMIRAN, Troitsk, Russia.
    Auroral electrojets and 3D currents in the ionosphere-magnetosphere system2006In: “Physics of Auroral Phenomena”, Proc. XXIX Annual Seminar, Apatity, Kola Science Centre, Russian Academy of Science , 2006, p. 25-30Conference paper (Other academic)
    Abstract [en]

    There are shortly described results of the analysis of variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. It is shown that the westward electrojet adjoins to the polar electrojet located at cusp latitudes in the dayside sector. The association of electrojets with the field-aligned currents (FACs), namely Region 1 FAC and Region 2 FAC is considered. During intense disturbances a Region 3 FAC (accompanied with diffuse electron precipitation from the plasma sheet boundary layer) with the downward current was identified. The analysis of observational data is summarized in terms of 2D time-latitude distribution of electrojets at ionospheric altitudes. The magnetic field sawtooth variations generated during the storm main and early recovery phases are also discussed. To follow 3D currents in the magnetosphereionosphere system a clarified view of interrelated 3D currents and magnetospheric plasma domains is presented.

  • 57.
    Feldstein, Y. I.
    et al.
    IZMIRAN, Troitsk, Russia.
    Prigancova, A.
    Vorobjev, V. G.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Starkov, G. V.
    Yagodkina, O. I.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    High-latitude electrojets and auroral luminosity and auroral particle precipitations2007In: “Physics of Auroral Phenomena”, Proc. XXX Annual Seminar, Apatity, Kola Science Centre, Russian Academy of Science , 2007, p. 55-59Conference paper (Other academic)
    Abstract [en]

    The mutual location of high-latitude electrojets, typical regions of the auroral luminosity and regions of auroral energy particle participations into the upper atmosphere under substorm conditions are considered. Three electrojets exist at high latitudes during substorm intervals: WE - westward electrojet, EE - eastward electrojet and PE – polar electrojet. Geomagnetic latitudes of the WE/EE and PE location vary depend on local time and magnetic activity level, respectively. It is shown that the WE is located within the limits of the auroral oval precipitation (AOP), the EE in the evening sector is located within the diffuse auroral zone (DAZ) and the PE near noon is located at the poleward AOP boundary shifting poleward with decreasing the magnetic activity level. The relationship of electrojets with different plasma domains in the magnetosphere is discussed.

  • 58. 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.

  • 59. Frey, H U
    et al.
    Haerendel, G
    Clemmons, J H
    Boehm, M H
    Vogt, J
    Bauer, O H
    Wallis, D D
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Luhr, H
    Freja and ground-based analysis of inverted-V events1998In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 103, no A3, p. 4303-4314Article in journal (Refereed)
    Abstract [en]

    During two campaigns, ground-based auroral observations were performed in coordination with Freja. The high temporal and spatial resolution of the satellite instruments as well as the real-time recording with a stereoscopic camera system from the ground enabled detailed comparison of small- and large-scale optical phenomena with particle and field data measured by the satellite. Three passes of the satellite over inverted-V auroral arcs and over precipitation regions with strong field-aligned electron spectra are investigated. Brightness modulations within auroral arcs coincide with modulations of primary electron fluxes. The dynamics of small-scale structures within arcs as well as the proper motion of arcs are analyzed and compared with electric fields measured by the satellite and with BARS radar measurements. Energy fluxes independently determined from the ground and from the satellite are used to calculate the field-aligned conductance. The results agree with predictions of the kinetic theory of the mirror force, if we allow for variations of the density and thermal energy of the electrons in the source region of the magnetosphere. Detailed comparison of electron spectra and electric and magnetic field perturbations provide evidence of different acceleration mechanisms for the electrons, electrostatic acceleration inside inverted-V's, and wave acceleration in transient regions.

  • 60.
    Gromova, L. I.
    et al.
    IZMIRAN, Troitsk, Russia.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Eriksson, Stefan
    University of Colorado, Boulder, CO, USA.
    Levitin, A. E.
    IZMIRAN, Troitsk, Russia.
    Feldstein, Y. I.
    IZMIRAN, Troitsk, Russia.
    High-Latitude Ionospheric Convection Patterns Dependent on the IMF Orientation2007In: Physics of Auroral Phenomena”, Proc. XXX Annual Seminar, Apatity, Kola Science Centre, Russian Academy of Science , 2007, p. 64-68Conference paper (Other academic)
    Abstract [en]

    The IZMEM model provides high-latitude ionospheric plasma convection patterns in both hemispheres as a function of the IMF orientation. Model electric potentials are compared with electric field measurements from the DE2, FAST and DMSP satellites along high-latitude passes of the Northern and Southern hemispheres during IMF Bz < 0 and By < 0 (By >0). It has been shown that the IZMEM model electric potentials are in good agreement with measurements along the satellite passes, which makes the IZMEM global spatial convection patterns for these plausible. For small IMF magnitude ionospheric convection patterns generally consist of two cells with a positive potential cell on the dawn-side and a negative potential cell on the dusk-side. For IMF By<0 (By>0) a positive (negative) potential cell becomes dominant in the northern hemisphere, and oppositely in the southern hemisphere. During Bz > 0 the convection pattern changes from the standard two-cell pattern to a more complicated one. IZMEM shows two additional convection cells in the dayside polar cap, positive (negative) potential cell is present duskward (dawnward) of the noon-midnight meridian, and may cause three-cell or four-cell convection pattern depending on By/Bz ratio.

  • 61. Horbury, T.
    et al.
    Louarn, P.
    Fujimoto, M.
    Baumjohann, W.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Barabash, S.
    Canu, P.
    Glassmeier, K. -H
    Koskinen, H.
    Nakamura, R.
    Owen, C.
    Pulkkinen, T.
    Roux, A.
    Sauvaud, J. -A
    Schwartz, S. J.
    Svenes, K.
    Vaivads, A.
    Cross-scale: A multi-spacecraft mission to study cross-scale coupling in space plasmas2006In: European Space Agency, (Special Publication) ESA SP, 2006, no 598, p. 561-568Conference paper (Refereed)
    Abstract [en]

    Collisionless astrophysical plasmas exhibit complexity on many scales: if we are to understand their properties and effects, we must measure this complexity. We can identify a small number of processes and phenomena, one of which is dominant in almost every space plasma region of interest: shocks, reconnection and turbulence. These processes act to transfer energy between locations, scales and modes. However, this transfer is characterised by variability and 3D structure on at least three scales: electron kinetic, ion kinetic and fluid. It is the nonlinear interaction between physical processes at these scales that is the key to understanding these phenomena and predicting their effects. However, current and planned multi-spacecraft missions such as Cluster and MMS only study variations on one scale in 3D at any given time - we must measure the three scales simultaneously fully to understand the energy transfer processes. We propose a mission, called Cross-Scale, to study these processes. Cross-Scale would comprise three nested groups, each consisting of up to four spacecraft. Each group would have a different spacecraft separation, at approximately the electron and ion gyroradii, and a larger MHD scale. We would therefore be able to measure variations on all three important physical scales, simultaneously, for the first time. The spacecraft would fly in formation through key regions of near-Earth space: The solar wind, bowshock, magnetosheath, magnetopause and magnetotail.

  • 62. Janhunen, P.
    et al.
    Olsson, A.
    Tsyganenko, N. A.
    Russell, C. T.
    Laakso, H.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Statistics of a parallel Poynting vector in the auroral zone as a function of altitude using Polar EFI and MFE data and Astrid-2 EMMA data2005In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 5, p. 1797-1806Article in journal (Refereed)
    Abstract [en]

    We study the wave-related (AC) and static (DC) parallel Poynting vector (Poynting energy flux) as a function of altitude in auroral field lines using Polar EFI and MFE data. The study is statistical and contains 5 years of data in the altitude range 5000-30 000km. We verify the low altitude part of the results by comparison with earlier Astrid-2 EMMA Poynting vector statistics at 1000km altitude. The EMMA data are also used to statistically compensate the Polar results for the missing zonal electric field component. We compare the Poynting vector with previous statistical DMSP satellite data concerning the electron precipitation power. We find that the AC Poynting vector (Alfvenwave related Poynting vector) is statistically not sufficient to power auroral electron precipitation, although it may, for K-P> 2, power 25-50% of it. The statistical AC Poynting vector also has a stepwise transition at R=4 R-E, so that its amplitude increases with increasing altitude. We suggest that this corresponds to Alfven waves being in Landau resonance with electrons, so that wave-induced electron acceleration takes place at this altitude range, which was earlier named the Alfven Resonosphere (ARS). The DC Poynting vector is similar to 3 times larger than electron precipitation and corresponds mainly to ionospheric Joule heating. In the morning sector (02:00-06:00 MLT) we find that the DC Poynting vector has a nontrivial altitude profile such that it decreases by a factor of similar to 2 when moving upward from 3 to 4 RE radial distance. In other nightside MLT sectors the altitude profile is more uniform. The morning sector nontrivial altitude profile may be due to divergence

  • 63.
    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.

  • 64. Kasaba, Y.
    et al.
    Bougeret, J. L.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kojima, H.
    Yagitani, S.
    Moncuquet, M.
    Trotignon, J. G.
    Chanteur, G.
    Kumamoto, A.
    Kasahara, Y.
    Lichtenberger, J.
    Omura, Y.
    Ishisaka, K.
    Matsumoto, H.
    MatsumotoJ, H.
    The Plasma Wave Investigation (PWI) onboard the BepiColombo/MMO: First measurement of electric fields, electromagnetic waves, and radio waves around Mercury2010In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 58, no 1-2, p. 238-278Article in journal (Refereed)
    Abstract [en]

    The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft includes the plasma and radio wave observation system called Plasma Wave Investigation (PWI). Since the receivers for electric field, plasma waves, and radio waves are not installed in any of the preceding spacecraft to Mercury, the PWI will provide the first opportunity for conducting in-situ and remote-sensing observations of electric fields, plasma waves, and radio waves in the Hermean magnetosphere and exosphere. These observations are valuable in studying structure, dynamics, and energy exchange processes in the unique magnetosphere of Mercury. They are characterized by the key words of the non-MHD environment and the peculiar interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM(2)P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10 MHz for the electric field and from 0.3 Hz to 640kHz for the magnetic field. From 2008, we will start the development of the engineering model, which is conceptually consistent with the flight model design. The present paper discusses the significance and objectives of plasma/radio wave observations in the Hermean magnetosphere, and describes the PWI sensors, receivers and their performance as well as the onboard data processing.

  • 65. Knudsen, D. J.
    et al.
    Whalen, B. A.
    Yau, A. W.
    Greffen, M. J.
    Eriksson, A. I.
    Lloyd, N.
    Boehm, M.
    Clemmons, J.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sub-kilometer thermal plasma structure near 1750 km altitude in the polar cusp/cleft1994In: Geophysical Research Letters, ISSN 00948276 (ISSN), Vol. 21, no 17, p. 1907-1910Article in journal (Refereed)
    Abstract [en]

    We present Freja Cold Plasma Analyzer (CPA) measurements from an encounter with the low altitude (approx.1750 km) polar cusp during which the CPA measured 2-D images of the thermal (0-16 eV) particle distributions at 1.2 s time resolution, and simultaneously made rapid estimates (600/s) of integrated thermal particle flux into the instrument. The high resolution data show bursty ion flux enhancements of the order of tens of percent on time scales of tens of ms, or alternatively, hundreds of m spatial scales. The flux of electrons from 0-16 eV also varied by tens of percent and on temporal/spatial scales comparable to those in the ion cases. There is some evidence that the thermal particle flux variations are associated with intense low-frequency electromagnetic fluctuations with temporal/spatial scales identical to those seen by the CPA (tens of ms. hundreds of m).

  • 66. Kullen, A
    et al.
    Blomberg, Lars
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The influence of IMF B-y on the mapping between the Earth's magnetotail and its ionosphere1996In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 23, no 18, p. 2561-2564Article in journal (Refereed)
    Abstract [en]

    It is well known that the dawn-dusk component of the interplanetary magnetic field (IMF) creates asymmetries in the magnetotail. The main effects are a weak nonuniform penetration of IMF B-y into the tail and a rotation of the whole tail current sheet. In this study we modify the Tsyganenko (1989) model to simulate the IMF B-y induced tail effects. By field line mapping we examine how different regions of the magnetosphere and ionosphere are influenced by the IMF By tail effects. The plasma sheet is shown to rotate around the central axis of the magnetotail. The mapping from the plasma sheet to the ionosphere for nonzero IMF B-y shows a change in the geometry of the auroral oval. The whole oval rotates, a local bulge occurs near midnight and the thickness of the oval is different in the morning and the evening sector. Simple geometrical considerations show that the tilting of the field lines caused by IMF B-y leads to a rotation of the oval, whereas the rotation of the tail current sheet is reponsible for the thickness variations along the oval. These results fit very well with the observed auroral distribution for an IMF with a dawnward or duskward direction.

  • 67.
    Kullen, A.
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Brittnacher, M.
    Cumnock, J. A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Blomberg, Lars G.
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Solar wind dependence of the occurrence and motion of polar auroral arcs: A statistical study2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, no A11Article in journal (Refereed)
    Abstract [en]

    [1] Polar UV images from a 3-month period in winter 1998-1999 are used for a statistical study of polar arcs. The study covers all auroral arcs that are located poleward of the northern auroral oval, and which are detectable by the UV imager. The arcs are examined with respect to their spatial and temporal behavior as well as to a possible connection to solar wind parameters using ACE satellite data. It is found that the majority of polar arcs appear during northward IMF, strong IMF magnitude, and high solar wind speed. A modified Akasofu-Perreault epsilon parameter with a cosine function instead of a sine function (nuB(2) cos(4) (theta/2)(l(0)(2)/mu(0))) combines these results. It correlates well with the occurrence frequency of polar arcs for long timescales. The location of polar arcs is strongly dependent on the sign of the IMF B-y component. Static polar arcs occur in the Northern Hemisphere on the dawn (dusk) side of the oval for negative (positive) IMF B-y, whereas poleward-moving arcs separate from the opposite side of the oval, and then move in the direction of IMF B-y. All polar arcs are sorted into five different categories according to their spatial structure and evolution: oval-aligned, bending, moving, midnight, and multiple arcs. Each polar arc type occurs for a characteristic combination of solar wind parameters. IMF clock angle changes seem to have a strong influence on what type of arc occurs. Oval-aligned arcs appear mainly during steady IMF, bending arcs after an IMF B-z sign change, and moving arcs after an IMF B-y sign change. For the rare midnight and multiple arc events, no characteristic IMF clock angle dependence has been found. The different types of clear polar arcs are discussed in the context of existing observational studies and transpolar arc models.

  • 68.
    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)
  • 69.
    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)
  • 70.
    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.

  • 71.
    Lönnqvist, Håkan
    et al.
    Swedish Institute of Space Physics, Uppsala.
    ANDRE, M
    MATSON, L
    BAHNSEN, A
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    ERLANDSON, RE
    Generation of VLF saucer emissions observed by the Viking satellite1993In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 98, p. 13565-13574Article in journal (Refereed)
    Abstract [en]

    Simultaneous observations by the Viking satellite of electric and magnetic fields as well as charged particles have been used to investigate V-shaped wave phenomena. The intensity of these VLF and ELF emissions is V-shaped when shown in a frequency versus time plot. Simultaneous observations of V-shaped so-called VLF saucer emissions, particles and field-aligned currents strongly suggest, for the first time, that upgoing electrons with energies less than a few hundred electron volts can generate these waves. Broadband waves observed inside the saucer generation region, form frequencies much less than the ion cyclotron frequency up to the plasma frequency, may also be generated by these electrons. Viking observations of VLF saucers at altitudes between 4000 km and 13,500 km show that these emissions occur at higher altitudes tha discussed in previous reports. The generation regions seem to be more extended at these higher altitudes than what has been reported at lower altitudes by other observations.

  • 72.
    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.

  • 73.
    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.

  • 74.
    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.

  • 75.
    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.

  • 76.
    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)
  • 77.
    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.

  • 78.
    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)
  • 79.
    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)
  • 80.
    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.
    Fälthammar, C. -G
    KTH, Superseded Departments, Alfvén Laboratory.
    Haerendel, G.
    Mozer, F. S.
    Pedersen, A.
    Tanskanen, P.
    The double probe electric field experiment on Freja: Experiment description and first results1994In: Space Science Reviews, ISSN 00386308 (ISSN), Vol. 70, no 3-4, p. 483-508Article in journal (Refereed)
    Abstract [en]

    A description is given of the Freja double-probe electric field instrument. Its capability to perform high-resolution measurements of the aurora and its fine-structure as well as collect information on sub-auroral and low-latitude phenomena is illustrated by selected results from the first six months of operation. The instrument is highly flexible and possible to operate in a number of different modes. It is also equipped with a 4-Megabyte burst memory for high data sampling rate and temporary storage of data. It has been fully operational since October 1992, and delivers data from ≈22 hr day-1 including about 5-6 auroral crossings of the northern and southern auroral ionosphere. New and important information on the auroral fine structure and electrodynamics is obtained by means of burst resolution data (6144 samples s-1) and normal resolution data (768 samples s-1). Common burst data collection triggered by the electric field event detector has turned out to be very useful for the selection of scientifically interesting events. This is illustrated by high-resolution data of a pair of extremely intense and narrow electric field structures (1 V m-1) which are associated with a total absence of precipitating particles, depletions of the thermal plasma and with an intense wave activity. The low inclination of the Freja orbit provides a new perspective for studying largescale phenomena associated with east-west gradients as is exemplified by electric field data from a satellite crossing over north-south oriented auroral structures presumably resulting from rotational distortions of east-west aligned auroral arcs. The different plasma regimes encountered by Freja are continuously monitored by means of current sweeps applied to the probes and by the satellite potential. In addition, overview data (8 samples s-1) are collected from full orbits and stored in the on-board memory and have proved to be extremely valuable, providing new information on global electric field phenomena at subauroral and lower latitudes, such as the intense poleward electric fields and Pc-1 observations that have been made near the plasmapause during substorm activity. © 1994 Kluwer Academic Publishers.

  • 81.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory.
    Haerendel, G.
    Mozer, F. S.
    Pedersen, A.
    Tanskanen, P.
    The Double Probe Electric Field Experiment on Freja: Desccription and First Results1993Report (Other academic)
  • 82.
    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.
    MURPHREE, JS
    ELPHINSTONE, RD
    ZANETTI, LJ
    ERLANDSON, RE
    SANDAHL, I
    DELABEAUJARDIERE, O
    OPGENOORTH, H
    RICH, FJ
    On the electrodynamic state of the auroral ionosphere during northward interplanetary magnetic field - a transpolar arc case study1991In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 96, no A6, p. 9567-9578Article in journal (Refereed)
    Abstract [en]

    The ionospheric electrodynamical state has been reconstructed for a transpolar arc event during northward interplanetary magnetic field conditions. An extensive set of observations by Viking and other satellites and by ground-based radars has been used to provide realistic model input data or to verify the modeling results. The resulting convection pattern is found to be consistent with the Viking electric field and intimately linked to the prevalent auroral distribution. It is characterized by a large evening cell, well extended across noon and split up by two separated potential minima, and a minor crescent-shaped morning cell. The convection signatures are found to vary a lot along the transpolar arc depending on the relative role of the arc-associated convection and the ambient convection. The transpolar arc is generally embedded in antisunward convective flow except near the connection points with the auroral oval, where sunward flow exists in localized regions.

  • 83.
    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.
    POTEMRA, TA
    MURPHREE, JS
    RICH, FJ
    STASIEWICZ, K
    A new method to derive instantaneous high-latitude potential distributions from satellite measurements including auroral imager data1987In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 14, no 4, p. 439-442Article in journal (Refereed)
  • 84.
    Marklund, Göran
    et al.
    KTH, Superseded Departments.
    Blomberg, Lars
    KTH, Superseded Departments.
    Stasiewicz, K.
    Murphree, J. S.
    Pottelette, R.
    Zanetti, L. J.
    Potemra, T. A.
    Hardy, D. A.
    Rich, F. J.
    Snapshots of High-Latitude Electrodynamics Using Viking and DMSP/F7 Observations1988Report (Other academic)
  • 85.
    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.
    STASIEWICZ, K
    MURPHREE, JS
    POTTELETTE, R
    ZANETTI, LJ
    POTEMRA, TA
    HARDY, DA
    RICH, FJ
    Snapshots of high-latitude electrodynamics using Viking and DMSP/F7 observations1988In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 93, no A12, p. 14479-14492Article in journal (Refereed)
  • 86.
    Marklund, Göran
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    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.
    Fälthammar, arl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Johnson, L
    Murphree, S
    Andersson, L
    Eliasson, L
    Opgenoorth, J
    Zanetti, J
    Observations of the electric field fine structure associated with the westward traveling surge and large-scale auroral spirals1998In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 103, no A3, p. 4125-4144Article in journal (Refereed)
    Abstract [en]

    The characteristics of the fine scale electric field associated with the westward traveling surge and large-scale auroral spirals and surges are investigated using high-resolution electric field, magnetic field, particle and UV imager observations from four eveningside auroral oval crossings by the Freja satellite. Three of the crossings were associated with signatures of auroral substorms and one crossing went directly through the head of a surge close in time and space to substorm onset. Three passes were adjacent to auroral spiral formations, one poleward of and one equatorward of such forms and one through the multiple arc region near the front of an extended region of auroral activity. The ambient electric field was found to intensify in the direction toward the spiral head (or the center of the auroral activity region) over a region comparable to the size of the visible auroral forms. These results confirm previous findings that the spiral or surge head is associated with negative space charge and an intense upward field-aligned current. The fourth pass, directly through the surge head reveals a very complicated structure of the surge region. Narrowly structured, intense (up to 700 mV/m) and mostly converging electric fields associated with intense electron precipitation (of both high and medium energies) and balanced field-aligned currents (up to 30 μA/m2) are seen near the edge of the surge head and adjacent to auroral structures in the wake. These narrow regions are embedded within more extended regions of intense high-energy electron precipitation but very weak electric fields and field-aligned currents. According to some existing models of the surge, a pronounced westward electric field component and a southward polarisation electric field is expected within the entire high-conductivity region but evidence in support of this was not found in the data. Rather, these suggest that a significant part of the upward surge current is closed by distributed downward field-aligned currents from the near surroundings. The Freja electric field is typically seen to intensify at the edges of or in-between bright auroral structures and to decrease within the arcs similar to what is observed in the ionosphere. The surge electric field is, however, much more intense than previously observed or anticipated at these altitudes with characteristics rather similar to those observed in the auroral acceleration region. Since the particle data indicate that most of the acceleration takes place above Freja altitudes, it seems as if Freja traversed the lower part of the auroral acceleration region associated with the surge.

  • 87.
    Marklund, Göran T.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars G.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Persson, S.
    Astrid-2, an advanced microsatellite for auroral research2001In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 19, no 6, p. 589-592Article in journal (Refereed)
    Abstract [en]

    The successful launch of the Swedish microsatellite Astrid-2 in December 1998 began a new era of auroral research, with advanced microprobes of 30 kg or less used as research tools. Innovative technologies and low-mass solutions were used for the sensors and deployment systems to allow a fairly complete set of scientific instruments within the 10 kg allocated for the scientific payload. A newly developed wire boom deployment system proved to function excellently. During its seven month lifetime Astrid-2 collected more than 26 Gbytes of high-quality data of auroral electric and magnetic fields, and auroral particle and plasma characteristics from approximately 3000 orbits at an inclination of 83 degrees and an altitude of about 1000 km. Scientific results cover a broad range of topics, from the physics of energization of auroral particles to how the magnetosphere responds to the energy input from the solar wind and global magnetic field modelling. The fulfilment of both the technological and the scientific mission objectives has opened entirely new possibilities to carry out low-budget multipoint measurements in near-Earth space.

  • 88. Matsumoto, H.
    et al.
    Bougeret, J. -L
    Blomberg, Lars G.
    KTH.
    Kojima, H.
    Yagitani, S.
    Omura, Y.
    Moncuquet, M.
    Chanteur, G.
    Kasaba, Y.
    Trotignon, J. -G
    Kasahara, Y.
    Plasma/radio wave observations at mercury by the bepicolombo mmo spacecraft2006In: Advances in Geosciences: Planetary Science (PS), World Scientific Publishing Co. , 2006, p. 83-84Chapter in book (Refereed)
    Abstract [en]

    The BepiColombo Mercury Magnetospheric Orbiter (MMO) spacecraft comprises the plasma and radio wave observation system called PlasmaWave Investigation (PWI). The PWI is designed and developed in collaboration between Japanese and European scientists. Since plasma/radio wave receivers were not installed in the former spacecraft, Mariner 10, which observed the planet Mercury, the PWI onboard the MMO spacecraft will provide the first plasma/radio wave data from Mercury orbit. It will give important information for studies of energy exchange processes in the unique magnetosphere of Mercury characterized by the interaction between the relatively large planet without ionosphere and the solar wind with high dynamic pressure. The PWI consists of three sets of receivers (EWO, SORBET, and AM2P), connected to two sets of electric field sensors (MEFISTO and WPT) and two kinds of magnetic field sensors (LF-SC and DB-SC). The PWI will observe both waveforms and frequency spectra in the frequency range from DC to 10MHz for the electric field.

  • 89. Mishin, V M
    et al.
    Block, L P
    KTH, Superseded Departments, Alfvén Laboratory.
    Bazarzhapov, A D
    Saifudinova, T I
    Lunyushkin, S B
    Shirapov, D S
    Woch, J
    Eliasson, L
    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.
    Opgenoorth, H
    A study of the CDAW 9C substorm of May 3, 1986, using magnetogram inversion technique 2, and a substorm scenario with two active phases1997In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 102, no A9, p. 19845-19859Article in journal (Refereed)
    Abstract [en]

    One of the CDAW 9C substorms is investigated in this paper using the database reported by Hones et al. and supplemented with magnetogram inversion technique (MIT) 2 data. These latter have provided information about the dynamics of the open tail magnetic Aux, current systems in the ionosphere, and the size and dynamics of the current wedge. We have identified the growth: expansion, and recovery phases of this substorm, with characteristics expected from a generally accepted scenario. However, specific signatures were observed in the interval (0919-0935) UTI i.e., between the growth and expansion phases, indicating the concurrent development of the substorm onset and corresponding instabilities in the innermost current sheet, and small-scale cross-tail current disruptions without the open tail reconnection. In addition to signatures of small-scale dipolarization, an increase of the open tail magnetic flux, and a current system of the type close to DP 2 were observed at (0919-0935) UT, which is more likely to suggest predominance of the tail-stretching process than magnetic collapse, This fact was interpreted in tel ms of a relevant simple model as a signature of the growth of the energy input from the solar wind which ensures the observable disturbance power. Hence the disturbance st (0919-0935) UT was more likely a driven one than an unloading one. The aforementioned signatures make it possible to identify the interval (0919-0935) UT as the ''phase of multiple onsets'' or: (equivalently) the ''first active phase,'' which was previously defined by Mishin [1991., and references therein] as one of the four standard phases of a typical substorm (in addition to the expansion phase). Thus the case study supports the substorm scenario with two active phases and, accordingly, with two different kinds of physics, This case study illustrates also the informativity of MIT 2 data and their ability to effectively complement the database traditionally used in substorm studies.

  • 90. Miyoshi, Y.
    et al.
    Ono, T.
    Takashima, T.
    Asamura, K.
    Hirahara, M.
    Kasaba, Y.
    Matsuoka, A.
    Kojima, H.
    Shiokawa, K.
    Seki, K.
    Fujimoto, M.
    Nagatsuma, T.
    Cheng, C. Z.
    Kazama, Y.
    Kasahara, S.
    Mitani, T.
    Matsumoto, H.
    Higashio, N.
    Kumamoto, A.
    Yagitani, S.
    Kasahara, Y.
    Ishisaka, K.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fujimoto, A.
    Katoh, Y.
    Ebihara, Y.
    Omura, Y.
    Nosé, M.
    Hori, T.
    Miyashita, Y.
    Tanaka, Y. -M
    Segawa, T.
    The energization and radiation in geospace (ERG) project2012In: Dynamics of The Earth's Radiation Belts and Inner Magnetosphere, American Geophysical Union (AGU), 2012, Vol. 199, p. 103-116Conference paper (Refereed)
    Abstract [en]

    The Energization and Radiation in Geospace (ERG) project for solar cycle 24 will explore how relativistic electrons in the radiation belts are generated during space storms. This geospace exploration project consists of three research teams: the ERG satellite observation team, the ground-based network observation team, and the integrated data analysis/simulation team. Satellite observation will provide in situ measurements of features such as the plasma distribution function, electric and magnetic fields, and plasma waves, whereas remote sensing by ground-based observations using, for example, HF radars, magnetometers, optical instruments, and radio wave receivers will provide the global state of the geospace. Various kinds of data will be integrated and compared with numerical simulations for quantitative understanding. Such a synergetic approach is essential for comprehensive understanding of relativistic electron generation/loss processes through crossenergy and cross-regional coupling in which different plasma populations and regions are dynamically coupled with each other. In addition, the ERG satellite will utilize a new and innovative measurement technique for wave-particle interactions that can directly measure the energy exchange process between particles and plasma waves. In this paper, we briefly review some of the profound problems regarding relativistic electron accelerations and losses that will be solved by the ERG project, and we provide an overview of the project.

  • 91. Moncuquet, M.
    et al.
    Matsumoto, H.
    Bougeret, J-L
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Issautier, K.
    Kasaba, Y.
    Kojima, H.
    Maksimovic, M.
    Meyer-Vernet, N.
    Zarka, P.
    The radio waves and thermal electrostatic noise spectroscopy (SORBET) experiment on BEPICOLOMBO/MMO/PWI: Scientific objectives and performance2006In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 38, no 4, p. 680-685Article in journal (Refereed)
    Abstract [en]

    SORBET (Spectroscopie des Ondes Radio and du Bruit Electrostatique Thermique) is a radio HF spectrometer designed for the radio and Plasma Waves Instrument onboard BepiColombo/Mercury Magnetospheric Orbiter (MMO), which performs remote and in situ measurements of waves (electromagnetic and electrostatic). Technically, SORBET includes a plasma wave spectrometer, with two E-field inputs from the two perpendicular electric antennas and one B-field input from a search coil, in the range 2.5-640 kHz. This frequency band includes the local gyrofrequency and plasma frequency expected on most part of the MMO orbits. SORBET also includes a higher frequency radio receiver for remote sensing in the range 500 kHz-10.2 MHz. Owing to its capabilities, SORBET will be able to address the following scientific objectives: High resolution mapping(similar to 30 km) of electron density and temperature in the solar wind and in the Hermean magnetosphere and exo-ionosphere, via the technique of Quasi-Thermal Noise (QTN) spectroscopy. These QTN measurements will be determinant for the dynamic modeling of the magnetosphere and will provide a fundamental input for the chemistry of cold ionized species (Na, K, O, . . .) in Mercury's environment. Detection and study of Hermean radio emissions, including possible cyclotron emissions (up to similar to 10-20 kHz) from mildly energetic electrons in most highly magnetized (polar?) regions, and possible synchrotron radiation (up to a few MHz?) from more energetic electrons. Monitoring of solar radio emissions up to similar to 10 MHz in order to create a solar activity index from the view point of Mercury, allowing to correlate it with the Hermean magnetospheric response. We especially discuss the capabilities of SORBET for performing the QTN spectroscopy in Mercury's magnetosphere, using the two electric dipole antennas equipping MMO, called MEFISTO and WPT.

  • 92.
    Mursula, Kalevi
    et al.
    University of Oulu.
    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.
    BRAYSY, T
    RASINKANGAS, R
    TANSKANEN, P
    Dispersive Pc1 bursts observed by Freja1994In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 21, no 17, p. 1851-1854Article in journal (Refereed)
    Abstract [en]

    Electric field measurements by the Freja double probe sensor are used to study equatorially generated ion cyclotron waves, also called Pc1 pulsations. We have examined the global occurrence and spectral properties of these waves in the upper ionosphere during 12-hour period on Nov. 18, 1992, when a long chain of structured Pc1 waves (pearls) was observed on ground. In agreement with ground observations, Pc1 waves were found to occur as short bursts of 10-25 s in early morning to postnoon MLT sector. Most Pc1 activity was detected within a small latitudinal range, extending from 60-degrees CGMlat at dawn to 630 CGMlat at noon. The latitudinal width of the source was only about 0.5-degrees CGMlat. Observations give evidence for a plasmapause connected source region that was several hours wide in MLT and active during many hours. One burst displayed a fully developed classical dispersive Pc1 pearl, now detected for the first time above the ionosphere. In all studied Pc1 events, two spectral maxima (bands) were observed. The longer Pc1 wave bursts showed evidence for a small time delay between the lower and upper frequency bands, unveiling a new dispersive phenomenon.

  • 93. Norqvist, P
    et al.
    Andre, M
    Eliasson, L
    Eriksson, A I
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Luhr, H
    Clemmons, J H
    Ion cyclotron heating in the dayside magnetosphere1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A6, p. 13179-13193Article in journal (Refereed)
    Abstract [en]

    Observations of waves and particles obtained by the Freja satellite at altitudes around 1700 km in the dayside high-latitude magnetosphere are used to study ion energization. We find that ions, including O+, during several events of intense ion energization can be heated perpendicularly to the geomagnetic field to mean energies df up to about 20 eV via the process of cyclotron resonance by broadband waves around the ion gyrofrequencies. There is a good correlation between such broadband waves and the ion energization. The waves show no spectral features at the O+ gyrofrequency. The observed wave amplitudes are used as an input to a Monte Carlo simulation to obtain the observed ion energies. The waves around the ion gyrofrequencies may be generated either by field-aligned electrons or by nonlinear processes transferring energy from waves with lower frequencies. Not only the mean energy but also the shape of the particle distribution agrees with the cyclotron resonance heating mechanism. Other mechanisms, such as heating by lower hybrid waves or by a slowly varying electric field, are investigated but are found to be less important than cyclotron heating in this region of space.

  • 94. Norqvist, P
    et al.
    Oscarsson, T
    Andre, M
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Isotropic and perpendicular energization of oxygen ions at energies below 1 eV1998In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 103, no A3, p. 4223-4239Article in journal (Refereed)
    Abstract [en]

    We present observations of low-energy O+ ion distributions obtained by the Freja satellite at altitudes between 1100 and 1600 km in the dayside high-latitude magnetosphere. The particle observations are obtained by the Freja ion mass spectrometer designed to observe ion energies up to several keV. We show that such instruments can also be used to accurately measure temperatures less than 1 eV, by operating the instrument at a fixed energy level of a few eV. When the mass spectrometer is operated at an energy approximately equal to the energy of O+ ions moving with the satellite velocity (several km/s), the satellite motion and the detector viewing directions become important. The idea is that the satellite ram effect together with different instrument viewing directions related to the satellite spin can allow sampling of different regions of ion velocity space. We find that isotropic O+ energization dominates at mean energies below about 0.4 eV, while energization perpendicular to the geomagnetic field dominates at higher energies. The isotropic ion distributions may exhibit a bulk motion up or down along the geomagnetic field, while the perpendicularly heated distributions are moving upward. The perpendicular energization occurs in the dayside auroral region including the cusp/cleft, the source region of the so-called cleft ion fountain. The perpendicular heating to a few eV can be associated with weak broadband low-frequency electric wave fields, similar to the stronger emissions causing O+ energization to hundreds of eV. However, at low energies other mechanisms map also be important.

  • 95. Ohtani, S
    et al.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Newell, P T
    Yamauchi, M
    Potemra, T A
    Zanetti, L J
    Altitudinal comparison of dayside field-aligned current signatures by viking and DMSP-F7: Intermediate-scale field-aligned current systems1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A7, p. 15297-15310Article in journal (Refereed)
    Abstract [en]

    Dayside large-scale and intermediate-scale field-aligned current (FAG) signatures are examined with multi-instrument measurements from Viking and DMSP-F7 at magnetic conjunctions. The present paper reports four such conjunction events, with an emphasis on an event that occurred on October 13, 1986. In these four events both Viking and DMSP-F7 crossed prenoon FAC systems approximately along meridians. The altitude of DMSP-F7 was 835 km, whereas that of Viking ranged from 8500 to 12,000 km. The electric to magnetic field ratio measured by Viking indicates that intermediate-scale FAC systems, as well as large-scale FAC systems, are often quasi-stationary, This is also supported by the comparison between the Viking and DMSP-F7 magnetic measurements. The only obvious exception is the equatorward part of the October 13 event, in which the Viking and DMSP-F7 measurements are better explained in terms of Alfven waves. In two other events the Viking signature projected to the DMSP-F7 altitude is significantly more structured than the DMSP-F7 signature, although the electric to magnetic field ratio observed by Viking suggests that the associated FACs were quasistationary. This apparent discrepancy is possibly ascribed to the fact that Viking stays longer in FAC systems and therefore has more chance to observe temporal changes in FACs. However, such temporal effects must operate longer than the Alfven transit time so that FAC systems become quasi-stationary. Although the generation mechanism(s) of intermediate-scale FAC systems remains an open question, possibilities include a localized shear of plasma convection and a localized merging between the solar wind and magnetospheric field lines.

  • 96. Ohtani, S
    et al.
    Elphinstone, R D
    Troshichev, O A
    Yamauchi, M
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Zanetti, L J
    Potemra, T A
    Response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field1997In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 102, no A10, p. 22247-22260Article in journal (Refereed)
    Abstract [en]

    The response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field (IMF) is examined with multi-instrument data from the Viking and DMSP-F7 satellites as well as ground magnetometer data. The event selected, which occurred on October 5, 1986, was previously identified as a high-latitude dayside form by Murphree and Elphinstone [1988]. IMF B-Y was positive during most of the Viking auroral UV observation, whereas IMF B-Z made a transient southward excursion, followed by a sharp increase to +8 nT. The results are summarized as follows: (1) There were two auroral belts extending westward from the early afternoon sector. The equatorward belt was persistent throughout the event and was embedded in the CPS/BPS precipitation region, whereas the poleward belt was in the open field line region and was associated with northward IMF B-Z. (2) A new auroral spot emerged in the afternoon sector just poleward of the previously active region, delayed 10 min from the sudden increase in IMF B-Z. This time lag is ascribed to the travel time of the new IMF orientation from the subsolar point to a solar wind-magnetosphere interaction site tailward of the dayside cusp, as well as to the response time of the dayside auroral acceleration process. (3) The new auroral activity expanded both eastward and westward during the first few minutes and then expanded primarily westward across the noon meridian, forming the poleward belt. The speed of the westward extension in the second phase was comparable to the speed of the ionospheric convection. (4) The dayside auroral process has a finite decay constant, which is inferred to be at least 10 min. (5) The response time of the midday ionospheric convection to IMF variations is estimated to be a few to several minutes.

  • 97. Ohtani, S.
    et al.
    Korth, H.
    Brandt, P. C.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Singer, H. J.
    Henderson, M. G.
    Lucek, E. A.
    Frey, H. U.
    Zong, Q.
    Weygand, J. M.
    Zheng, Y.
    Lui, A. T. Y.
    Cluster observations in the inner magnetosphere during the 18 April 2002 sawtooth event: Dipolarization and injection at r=4.6 R-E2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no A8Article in journal (Refereed)
    Abstract [en]

    The present study examines a sawtooth injection event that took place around 0800 UT on 18 April 2002 when the Cluster spacecraft were located in the inner magnetosphere in the premidnight sector. In association with this injection, Cluster, at a radial distance of 4.6 RE, observed that the local magnetic field became more dipolar and that both ion and electron fluxes increased without notable energy dispersion. These features were accompanied by intensifications of the equatorward component of a double- oval structure and also by an enhancement of the ring- current oxygen ENA flux. The event was also accompanied by large magnetic field ( a few tens of nT) and electric field ( a few tens of mV/ m) fluctuations with characteristic timescales of a few tens of seconds. These observations strongly suggest that this sawtooth injection extended not only widely in local time but also deeply into the inner magnetosphere. Interestingly, Cluster repeatedly observed dipolarization- like signatures afterward, which, however, were not associated with enhancements of local energetic ion flux or with geosynchronous dipolarization or injection signatures. Instead, these magnetic signatures were accompanied by oscillatory plasma motion in the radial direction with a characteristic timescale of about 10 min, which appears to be related to the westward propagation of a spatially periodic auroral structure. The associated azimuthal electric field component was well correlated with the time derivative of the north- south magnetic field component, suggesting that the observed electric field is inductive. These findings suggest that electromagnetic processes far inside geosynchronous orbit play an important role in energization of energetic ions and auroral dynamics during magnetospheric storms.

  • 98. Ohtani, S
    et al.
    POTEMRA, TA
    NEWELL, PT
    ZANETTI, LJ
    IIJIMA, T
    WATANABE, M
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    ELPHINSTONE, RD
    MURPHREE, JS
    YAMAUCHI, M
    WOCH, JG
    4 Large-scale field-aligned current systems in the dayside high-latitude region1995In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 100, p. 137-153Article in journal (Refereed)
    Abstract [en]

    A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and DMSP-F7 crossings of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the CPS precipitation region, often overlapping with the BPS at its poleward edge, and is interpreted as a region 2 current. The pair of downward and upward FACs in the middle of the structure are collocated with structured electron precipitation. The precipitation of high-energy (>1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simultaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region 0) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B-Y, We discuss the FAC structure in terms of three types of convection cells: the merging, viscous, and lobe cells. During strongly negative IMF B-Y two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitudinal overlap of midday and morning FAC systems. We suggest that the four-current sheet structure is common in a certain prenoon local time sector during strongly negative IMF B-Y.

  • 99. Ohtani, S
    et al.
    Potemra, T.A.
    Newell, P.T.
    Zanetti, L.J.
    Iijima, T.
    Watanabe, M.
    Yamauchi, M.
    Elphinstone, R.D.
    Delabeaujardiere, O.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory.
    Simultaneous prenoon and postnoon observations of 3 field-aligned current systems from Viking and DMSP F71995In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 100, no A1, p. 119-136Article in journal (Refereed)
    Abstract [en]

    The spatial structure of dayside large-scale field-aligned current (FAG) systems is examined by using Viking and DMSP-F7 data. We focus on four events in which the satellites simultaneously observed postnoon and prenoon three FAC systems: the region 2, the region 1, and the mantle (referred to as midday region 0) systems, from equatorward to poleward. These events provide the most solid evidence to date that the midday region 0 system is a separate and unique FAC system, and is not an extension of the region 1 system from other local times. The events are examined comprehensively by making use of a multi-instrument data set, which includes magnetic field, particle flux, electric field, auroral UV image data from the satellites, and the Sondrestrom convection data. The results are summarized as follows: (1) Region 2 currents flow mostly in the CPS precipitation region, often overlapping with the BPS at their poleward edge. (2) The region 1 system is located in the core part of the auroral oval and is confined in a relatively narrow range in latitude which includes the convection reversal. The low-latitude boundary layer, possibly including the outer part of the plasma sheet, and the external cusp are the major source regions of dayside region 1 currents. (3) Midday region 0 currents flow on open field lines and are collocated with the shear of antisunward convection flows with velocities decreasing poleward. On the basis of these results we support the view that both prenoon and postnoon current systems consist of the three-sheet structure when the distortion of the convection pattern associated with interplanetary magnetic field (IMF) B-y is small and both morningside and eveningside convection cells are crescent-shaped. We also propose that the midday region 0 and a part of the region 1 systems are closely coupled to the same source.

  • 100. Olsson, Annika
    et al.
    Janhunen, Pekka
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Ivchenko, Nickolay V.
    KTH, Superseded Departments, Alfvén Laboratory.
    Blomberg, Lars G.
    KTH, Superseded Departments, Alfvén Laboratory.
    Statistics of Joule heating in the auroral zone and polar cap using Astrid-2 satellite Poynting flux2004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 12, p. 4133-4142Article in journal (Refereed)
    Abstract [en]

    We make a statistical study of ionospheric Joule heating with the Poynting flux method using six months of Astrid-2/EMMA electric and magnetic field data during 1999 (solar maximum year). For the background magnetic field we use the IGRF model. Our results are in agreement with earlier statistical satellite studies using both the Sigma(P)E(2) method and the Poynting flux method. We present a rather comprehensive set of fitted Joule heating formulas expressing the Joule heating in given magnetic local time (MLT) and invariant latitude (ILAT) range under given solar illumination conditions as a function of the K-P index, the AE index, the Akasofu epsilon parameter and the solar wind kinetic energy flux. The study thus provides improved and more detailed estimates of the statistical Joule heating. Such estimates are necessary building blocks for future quantitative studies of the power budget in the magnetosphere and in the nightside auroral region.

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