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  • 101. Orsini, S.
    et al.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Delcourt, D.
    Grard, R.
    Massetti, S.
    Seki, K.
    Slavin, J.
    Magnetosphere-exosphere-surface coupling at Mercury2007In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 132, no 04-feb, p. 551-573Article in journal (Refereed)
    Abstract [en]

    Mercury's environment is a complex system, resulting from the interaction between the solar wind, magnetosphere, exosphere and surface. A comprehensive description of its characteristics requires a detailed study of these four elements. This paper illustrates and discusses the key processes that are implicated in the strong coupling of the Hermean magnetosphere with the other elements. The magnetosphere of Mercury, frequently called mini- magnetosphere, when compared to that of Earth, plays a significant role in controlling the planet source and loss processes, by means of both particle and field interactions. We review the status of our knowledge, and give possible interpretations of the still-limited data set presently available.

  • 102. Oster, J.
    et al.
    Collier, A. B.
    Hughes, A. R. W.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lichtenberger, J.
    Spatial correlation between lightning strikes and whistler observations from Tihany, Hungary2009In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 105, no 5-6, p. 234-237Article in journal (Refereed)
    Abstract [en]

    A whistler is a very low frequency (VLF) phenomenon that acquires its characteristics from dispersive propagation in the magnetosphere. Whistlers are derived from the intense VLF radiation produced in lightning strikes, which can travel great distances within the Earth-ionosphere waveguide (EIWG) before penetrating the ionosphere, and exciting a duct. Field-aligned ducts of enhanced plasma density guide the propagation from one hemisphere to the other. The location of the duct, relative to the strike that causes the whistler, is unknown. Whistler time series from Tihany, Hungary, have been cross-correlated with lightning data obtained from the World Wide Lightning Location Network (WWLLN). The results show that whistlers observed at Tihany originate mainly from lightning strikes in an area with a radius of approximately 1 000 km surrounding the magnetic conjugate point in the Indian Ocean just east of East London, South Africa. A clear diurnal distinction was seen in that the correlation is maximised when the whistler station and the source region are in darkness. This is believed to relate to the diurnal variation of the ionosphere, which becomes more transparent to VLF waves at night.

  • 103.
    Persson, M. A. L.
    et al.
    Swedish Institute of Space Physics, Uppsala.
    OPGENOORTH, HJ
    PULKKINEN, TI
    ERIKSSON, AI
    DOVNER, PO
    REEVES, GD
    BELIAN, RD
    ANDRE, M
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    ERLANDSON, RE
    BOEHM, MH
    AIKIO, AT
    HAGGSTROM, I
    Near-Earth substorm onset - a coordinated study1994In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 21, no 17, p. 1875-1878Article in journal (Refereed)
    Abstract [en]

    We present simultaneous satellite and ground-based measurements of a substorm. Throughout the initial substorm expansion, southward drifting arcs are observed poleward of the expanding substorm aurora, indicating two independent systems of particle precipitation. Freja passes the brightening onset arc in the topside ionosphere near the moment of the substorm onset, observing an Alfven wave, field aligned current and oxygen ion outflow. The substorm onset occurs at low magnetospheric L-shells, near the poleward edge of the region of trapped particles. The location and time for the substorm injection are confirmed by geostationary spacecraft together with magnetometers, all-sky cameras and radar on the ground. We believe that the substorm onset may be triggered by modification of the oxygen content of the inner magnetosphere during the growth-phase caused by ionospheric ion outflow.

  • 104. Potemra, T A
    et al.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    A survey of Pc 5 pulsations in the dayside high-latitude regions observed by Viking1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A11, p. 24801-24813Article in journal (Refereed)
    Abstract [en]

    We have examined magnetic and electric field observations acquired with the polar orbiting Viking satellite near its 3 R(E) apogee and at local times from dawn through noon to dusk. Our objective was to determine the statistical properties of Pc 5 (150-600 s period) pulsations at different dayside local times and their relationship to large-scale Birkeland currents. The Viking data examined in detail here were acquired from 41 orbits during the period from March 26, 1986, to July 19, 1986. Pulsations could be readily identified on prenoon orbits as evidenced in a series of 10 consecutive orbits in one case and six consecutive orbits in another. The waveforms in the postnoon hours are more complicated than in the morning, and this made it more difficult to identify pulsations in this region. The simultaneous electric and magnetic field measurements from Viking were used to distinguish the magnetic variations associated with large-scale Birkeland currents from those associated with waves. These observations also made it possible to derive values for Pedersen and wave conductivities and Poynting fluxes for the waves. The average wave period for the 40 cases studied here is 4.8 min (frequency of 3.5 mHz), the average magnetic field amplitude is 30 nT, the average electric field amplitude (for the 11 cases when the electric field observations were available) is 7 mV/m, and the average incident Poynting flux is 85 mu W/m(2). The principal characteristics of the waves include the following: (1) From morning to noon, the magnetic field pulsations are polarized primarily in the east-west direction, and the associated electric field oscillations lag by 60 degrees-80 degrees and are polarized close to the north-south direction. Consequently, these pulsations are interpreted as the fundamental modes of resonant toroidal magnetic field oscillations. (2) In the afternoon hours, the magnetic field pulsations have a strong north-south component and include higher-frequency components (possibly the second harmonic). (3) In both the morning and afternoon hours, the pulsations occur 2 degrees-5 degrees equatorward of the interface between the counterflowing region 1 and region 2 Birkeland currents. (4) The average wave periods increase from similar to 3 min near 0800 magnetic local time (MLT) to similar to 5 min near noon. (5) The average wave amplitudes range from similar to 40 nT near 0900-1000 MLT to similar to 25 nT near 1300-1600 MLT.

  • 105. Potemra, T. A.
    et al.
    LUHR, H
    ZANETTI, LJ
    TAKAHASHI, K
    ERLANDSON, RE
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Block, L. P.
    KTH, Superseded Departments, Alfvén Laboratory.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    LEPPING, RP
    Mulitsatellite and ground-based observations of transient ULF waves1989In: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 94, no A3, p. 2543-2554Article in journal (Refereed)
  • 106. Saito, A
    et al.
    Iyemori, T
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Yamamoto, M
    Takeda, M
    Conjugate observations of the mid-latitude electric field fluctuations with the MU radar and the Freja satellite1998In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 60, no 1, p. 129-140Article in journal (Refereed)
    Abstract [en]

    Conjugate Freja satellite and MU radar observations were conducted from 1993 to 1995 to clarify the generation mechanism of mid-latitude electric field fluctuations (MEFs) which were found from DE-2 satellite observations. The detection of MEFs at higher altitudes than 1000 km by the Freja satellite confirms that the MEFs are transmitted along the geomagnetic held line without any significant damping. On one night of such conjugate observations, MEFs were observed in a traveling ionospheric disturbance (TID). On the other nights when the MEFs were observed by Freja, large scale density structures in the ionosphere were observed with the MU radar. Spread-F phenomena were also observed by ionosondes associated with these structures. The large scale modulation of the ionosphere, such as TIDs, might cause small scale modulations which grow through ionospheric instabilities. The linear growth rate is evaluated using a set of equations describing the growth of the mid-latitude ionospheric irregularities. The growth rate is shown to be too small under average conditions; however, when the neutral wind in TIDs is included, it is large enough to generate MEFs. (C) 1998 Elsevier Science Ltd. All rights reserved.

  • 107. Schaefer, S.
    et al.
    Glassmeier, K. H.
    Eriksson, P. T. I.
    Pierrard, V.
    Fornacon, K. H.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Spatial and temporal characteristics of poloidal waves in the terrestrial plasmasphere: a CLUSTER case study2007In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 25, no 4, p. 1011-1024Article in journal (Refereed)
    Abstract [en]

    Oscillating magnetic field lines are frequently observed by spacecraft in the terrestrial and other planetary magnetospheres. The CLUSTER mission is a very suitable tool to further study these Alfven waves as the four CLUSTER spacecraft provide for an opportunity to separate spatial and temporal structures in the terrestrial magnetosphere. Using a large scaled configuration formed by the four spacecraft we are able to detect a poloidal Ultra-Low-Frequency (ULF) pulsation of the magnetic and electric field in order to analyze its temporal and spatial structures. For this purpose the measurements are transformed into a specific field line related coordinate system to investigate their specific amplitude pattern depending on the path of the CLUSTER spacecraft across oscillating field lines. These measurements are then compared with modeled spacecraft observations across a localized poloidal wave resonator in the dayside plasmasphere. A detailed investigation of theoretically expected poloidal eigenfrequencies allows us to specify the observed 16 mHz pulsation as a third harmonic oscillation. Based on this we perform a case study providing a clear identification of wave properties such as an spatial scale structure of about 0.67 R-E. the azimuthal wave number m approximate to 30, temporal evolution, and energy transport in the detected ULF pulsations.

  • 108. Schafer, S.
    et al.
    Glassmeier, K. H.
    Eriksson, P. T. I.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Mager, P. N.
    Pierrard, V.
    Fornacon, K. H.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Schaefer, S.
    Spatio-temporal structure of a poloidal Alfven wave detected by Cluster adjacent to the dayside plasmapause2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 7, p. 1805-1817Article in journal (Refereed)
    Abstract [en]

    A case study of a poloidal ULF pulsation near the dayside plasmapause is presented based on Cluster observations of magnetic and electric fields. The pulsation is detected close to the magnetic equatorial plane at L shells L=[4.4, 4.6] and oscillates with a frequency of f=23 mHz. Investigating the wave energy flux reveals the standing wave nature of the observed pulsation. An estimation of the azimuthal wave number exposes a narrow azimuthal structure of the wave field with m approximate to 160. Spatial and temporal characteristics of the pulsation are analyzed in detail by representing data in a field line related coordinate system and a range-time-intensity representation. This allows an estimation of both the spatial extension of the wave field in the radial direction and its temporal decay rate. The analysis furthermore indicates that the same field lines are excited to a standing wave oscillation twice. Furthermore an accurate identification of a phase jump of the wave field across L shells is possible. Comparing the radial localization of the detected wave with theoretically expected field line eigenfrequencies reveals that the wave field is confined in the Alfven resonator at the outer edge of the plasmapause.

  • 109. Sundberg, K. Å. T.
    et al.
    Hughes, A. R. W.
    Collier, A. B.
    Eriksson, P. T. I.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Magnetic field oscillations at SANAE IV related to sudden increases in solar wind dynamic pressure2005In: South African Journal of Science, ISSN 0038-2353, E-ISSN 1996-7489, Vol. 101, no 12-nov, p. 539-543Article in journal (Refereed)
    Abstract [en]

    The magnetospheric response at times when sudden increases in the solar wind dynamic pressure cause terrestrial magnetic storms has been studied with data from the pulsation magnetometer at the South African Antarctic research base, SANAE IV. For solar wind events that lead to a sudden increase in the terrestrial magnetic field at Hermanus and Kakioka, related pulsations were found in the SANAE IV data. We studied seven solar wind events of special interest between 19 February 2003 and 18 February 2004. The events can be divided into two main pulsation groups: one group had a well-defined frequency and a duration of about 15 minutes, whereas the other had a less well-defined frequency content, longer duration and exhibited large amplitude fluctuations. The analysis confirms the conclusion that the measured response time of the magnetosphere to disturbances in the solar wind is broadly consistent with the propagation speed of magneto-hydrodynamic waves driven by solar wind dynamic pressure.

  • 110.
    Sundberg, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Properties of the Boundary Layer Potential for Northward Interplanetary Magnetic Field2009In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, no 11, p. L11104-Article in journal (Refereed)
    Abstract [en]

    We present a method for estimating the portion of the ionospheric high-latitude potential that maps to the magnetospheric boundary layer during steady northward IMF and global ionospheric 4-cell convection patterns associated with lobe reconnection, together with the results of a statistical study based on DMSP F13 data from 1996-2004. In comparison with a previous study for steady southward IMF by Sundberg et al. [2008], the results show significantly larger boundary layer potentials, with a mean value of 10 kV for the 271 events studied, corresponding to roughly 30-35% of the potential generated by the solar wind interaction. In a statistical analysis, the boundary layer potential is also shown to depend significantly on viscous parameters such as the solar wind velocity, density and pressure.

     

  • 111.
    Sundberg, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Statistical analysis of the sources of the cross-polar potential for southward IMF, based on particle precipitation characteristics2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no 8, p. L08103-Article in journal (Refereed)
    Abstract [en]

    There are several proposed physical processes which may contribute to the cross-polar potential and thus drive ionospheric convection around the polar caps. It is generally believed that magnetic reconnection is the dominant process, however dynamos such as viscous interaction and impulsive penetration are other possible contributors. A comprehensive statistical study has been conducted using data from the DMSP F13 satellite for passages along the northern hemisphere dawn-dusk meridian, with focus on typical two-cell convection patterns during times of steady southward IMF conditions. The results show that the low-latitude dynamo (viscous interaction or reconnection in the LLBL) on average accounts for only 1–2 kV of the total potential drop, values lower than those previously predicted. At rare occasions this dynamo can be a significant source of energy, however, contributing to more than 20 kV of the cross-polar potential.

  • 112.
    Sundberg, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Boardsen, S. A.
    Slavin, J. A.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Korth, H.
    The Kelvin-Helmholtz instability at Mercury: An assessment2010In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 58, no 11, p. 1434-1441Article in journal (Refereed)
    Abstract [en]

    The Kelvin-Helmholtz instability is believed to be an important means for the transfer of energy, plasma, and momentum from the solar wind into planetary magnetospheres, with in situ measurements reported from Earth, Saturn, and Venus. During the first MESSENGER flyby of Mercury, three periodic rotations were observed in the magnetic field data possibly related to a Kelvin-Helmholtz wave on the dusk side magnetopause. We present an analysis of the event, along with comparisons to previous Kelvin-Helmholtz observations and an investigation of what influence finite ion gyro radius effects, believed to be of importance in the Hermean magnetosphere, may have on the instability. The wave signature does not correspond to that of typical Kelvin-Helmholtz events, and the magnetopause direction does not show any signs of major deviation from the unperturbed case. There is thus no indication of any high amplitude surface waves. On the other hand, the wave period corresponds to that expected for a Kelvin-Helmholtz wave, and as the dusk side is shown to be more stable than the dawn side, we judge the observed waves not to be fully developed Kelvin-Helmholtz waves, but they may be an initial perturbation that could cause Kelvin-Helmholtz waves further down the tail. (C) 2010 Elsevier Ltd. All rights reserved.

  • 113.
    Sundberg, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Boardsen, S.A.
    Slavin, J.A.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cumnock, Judy A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Solomon, S. C.
    Anderson, B. J.
    Korth, H.
    Reconstruction of propagating Kelvin-Helmholtz vortices at Mercury's magnetopause2011In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 59, no 15, p. 2051-2057Article in journal (Refereed)
    Abstract [en]

    A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin-Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.

  • 114.
    Sundberg, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The Reverse Convection Potential:  A Statistical Study of the General Properties of Lobe Reconnection and Saturation Effects During Northward IMF2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 6, p. A06205-Article in journal (Refereed)
    Abstract [en]

    The saturation tendency of the cross-polar potential for southward interplanetary magnetic fields has been the subject of numerous studies, however, the behavior of the reverse convection potential when the IMF is northward remains less clear. In this study, we present a thorough statistical analysis of the 4-cell convection pattern associated with northward IMF and lobe reconnection, based on a large set of DMSP F13 satellite data. Results show a behavior much similar to the southward IMF case, with a clear saturation tendency of the reverse convection potential for strong solar wind electric fields both seen in the data and validated in the statistical analysis. The saturated potential level reaches a limit of about 60 kV, on the order of a fourth of the saturated potential seen for dayside reconnection during southward IMF.

  • 115. Trotignon, J. G.
    et al.
    Beghin, C.
    Lagoutte, D.
    Michau, J. L.
    Matsumoto, H.
    Kojima, H.
    Hashimoto, K.
    Kasaba, Y.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lebreton, J. P.
    Masson, A.
    Hamelin, M.
    Pottelette, R.
    Active measurement of the thermal electron density and temperature on the Mercury Magnetospheric Orbiter of the BepiColombo mission2006In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 38, no 4, p. 686-692Article in journal (Refereed)
    Abstract [en]

    The thermal component of Mercury's electron population has never been measured. One scientific objective of the Plasma Wave Investigation consortium, PWI, is to determine the influence of the thermal plasma upon the formation and dynamics of the planetary magnetosphere, as a function of solar activity. The Active Measurement of Mercury's Plasma experiment, AM(2)p, has been proposed as part of PWI, to monitor the density and temperature of the thermal electron population, during the whole mission of the Mercury Magnetospheric Orbiter of BepiColombo. These two physical parameters will be deduced from the measurements of the self- and mutual-impedances of the MEFISTO (Mercury Electric Field In Situ Tool) double-sphere antenna, in a frequency range comprising the expected plasma frequency. The in situ measurement of the antenna impedance is also essential for calibrating the electric antenna which measures the natural waves; it will allow, in particular, the effective length of the antenna to be calculated as a function of frequency and plasma conditions. The purpose of this paper is to define the scientific objectives of AM(2)p, to explain the principle of the measurement, to describe the electronic device, and to show the ability of AM 2p to make reliable and accurate measurements of the thermal plasma density and temperature in the Hermean magnetosphere, as well as in the solar wind at heliocentric distances of 0.31-0.47 AU. The potential performance of this instrument has been evaluated using both an analytical approach and numerical simulations.

  • 116. Vaivads, A
    et al.
    Andre, M
    Norqvist, P
    Oscarsson, T
    Ronnmark, K
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Clemmons, J H
    Santolik, O
    Energy transport during O+ energization by ELF waves observed by the Freja satellite1999In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 104, no A2, p. 2563-2572Article in journal (Refereed)
    Abstract [en]

    We present a study of strong ELF waves correlated with Of ion heating. We investigate the kinetic energy flux of oxygen ions and electrons parallel to the ambient magnetic field and the Poynting flux along the magnetic field of waves in different frequency regions. We show that the Poynting flux of lower hybrid waves and waves with frequencies below the oxygen gyrofrequency is downward but much less than the upgoing oxygen ion energy flux. The Poynting flux of ELF waves with frequencies at about half the local proton gyrofrequency is also downward, and it is comparable to, or larger, than the upward oxygen energy flux. Our results are consistent with a scenario where ELF waves with frequencies around half the proton gyrofrequency are generated above the satellite and transfer energy to oxygen ions in a region below the satellite.

  • 117. Vaivads, A.
    et al.
    André, M.
    Norqvist, P.
    Oscarsson, T.
    Rönnmark, K.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Clemmons, J. H.
    Santolik, O.
    Energy transport during O+ energization by ELF waves observed by the Freja satellite1999In: Journal of Geophysical Research A: Space Physics, ISSN 01480227 (ISSN), Vol. 104, no A2, p. 2563-2572Article in journal (Refereed)
    Abstract [en]

    We present a study of strong ELF waves correlated with O+ ion heating. We investigate the kinetic energy flux of oxygen ions and electrons parallel to the ambient magnetic field and the Poynting flux along the magnetic field of waves in different frequency regions. We show that the Poynting flux of lower hybrid waves and waves with frequencies below the oxygen gyrofrequency is downward but much less than the upgoing oxygen ion energy flux. The Poynting flux of ELF waves with frequencies at about half the local proton gyrofrequency is also downward, and it is comparable to, or larger, than the upward oxygen energy flux. Our results are consistent with a scenario where ELF waves with frequencies around half the proton gyrofrequency are generated above the satellite and transfer energy to oxygen ions in a region below the satellite. Copyright 1999 by the American Geophysical Union.

  • 118. Vaivads, A.
    et al.
    Eriksson, A. I.
    Andre, M.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Wahlund, J. -E
    Bale, S. D.
    Low-frequency electric field and density fluctuation measurements on Solar Orbiter2007In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 39, no 9, p. 1502-1509Article in journal (Refereed)
    Abstract [en]

    Solar Orbiter will orbit the Sun down to a distance of 0.22 AU allowing detailed in situ studies of important but unexplored regions of the solar wind in combination with coordinated remote sensing of the Sun. In-situ measurements require high quality measurements of particle distributions and electric and magnetic fields. We show that such important scientific topics as the identification of coronal heating remnants, solar wind turbulence, magnetic reconnection and shock formation within coronal mass ejections all require electric field and plasma density measurements in the frequency range from DC up to about 100 Hz. We discuss how such measurements can be achieved using the double-probe technique. We sketch a few possible antenna design solutions.

  • 119. Wahlund, J E
    et al.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Morooka, M
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Andre, M
    Eriksson, A I
    Kurth, W S
    Gurnett, D A
    Bale, S D
    Science opportunities with a double Langmuir probe and electric field experiment for JIMO2005In: PLANETARY ATMOSPHERES, IONOSPHERES, AND MAGNETOSPHERES, 2005, Vol. 36, no 11, p. 2110-2119Conference paper (Refereed)
    Abstract [en]

    The three icy Galilean moons of Jupiter: Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. They all have thin atmospheres with residence times of a few days at most. The surface interactions with the space environment determine the atmospheric and ionospheric properties. The Jupiter Icy Moons Orbiter (JIMO) gives possibilities to investigate the weathering properties of their surfaces and volatile material expelled from their interiors. The atmospheres and the ionized ionospheric components of the Galilean moons (including the volcanic moon Io) interact strongly with the co-rotating magnetosphere of Jupiter. This interaction is dynamic and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. The icy moon's ionospheres are likewise highly variable in time and estimated peak electron densities vary between 1000 and 20,000 cm(-3) near their surfaces. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months will give valuable insight into these processes. Foremost the LP measures in situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby provides estimates of key parameters for the dynamical behaviour of surface weathering and magnetospheric influences. In addition many other physical parameters important to the dynamics of these systems can be estimated with such an instrument, like the plasma flow and the DC electric field. Recent results from the LP part of the Radio and Plasma Wave Science (RPWS) on board the Cassini/Huygens spacecraft orbiting Saturn show that an LP works in extended plasma parameter domains with very good science return.

  • 120.
    Wahlund, Jan-Erik
    et al.
    Swedish Institute of Space Physics, Uppsala.
    Blomberg, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Morooka, Michiko
    Swedish Institute of Space Physics, Uppsala.
    André, Mats
    Swedish Institute of Space Physics, Uppsala.
    Eriksson, Anders
    Swedish Institute of Space Physics, Uppsala.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cold Plasma Diagnostics in the Jovian System: Brief Scientific Case and Instrumentation Overview2006In: Proceedings of the 6th IAA International Conference on Low-Cost Planetary Missions, 2006, p. 341-346Conference paper (Other academic)
    Abstract [en]

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

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

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

  • 121. Wang, D Y
    et al.
    Huang, G L
    Falthammar, C G
    KTH, Superseded Departments, Alfvén Laboratory.
    Lindqvist, Per-Arne
    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.
    Song, L T
    Nonlinear kinetic Alfven wave with Poisson equation correction in the low aurora1996In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 240, no 2, p. 175-186Article in journal (Refereed)
    Abstract [en]

    Nonlinear kinetic Alfven waves where beta much less than m(e)/m(i), have been solved both with and without the Poisson equation correction. It is found that the ratio of the perpendicular electric field and magnetic field, and the ratio of parallel and perpendicular electric field increase with deepening of the depressive density soliton. The former ratio may be larger than the Alfven velocity in the case of a large amplitude solitary kinetic Alfven wave. The Poisson equation correction is important for the nonlinear kinetic Alfven wave propagating along the magnetic field, which solves a puzzle of Sagdeev potential to approach infinity in the limit of K-x --> 0. This correction causes the solitary KAW possessing an electrostatic character along the direction of wave moving frame. These results have been compared with the observations from the Freja satellite in the low aurora.

  • 122. Wurz, Peter
    et al.
    Blomberg, Lars G.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Particle populations in Mercury's magnetosphere2001In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 49, no 14-15, p. 1643-1653Article in journal (Refereed)
    Abstract [en]

    Observations by Mariner 10 during its first and third flybys showed that Mercury possesses an intrinsic magnetic field resulting in a small magnetosphere that can keep the solar wind from directly interacting with the planet's surface under usual conditions. Since Mercury occupies a large fraction of its magnetosphere, regions of trapped charged particles in the inner magnetosphere, the plasmasphere and the energetic radiation belts, would all be absent. During the first flyby, energetic particle bursts were detected and interpreted as hermean substroms analogous to the terrestrial magnetosphere. Moreover, during this flyby, ULF waves and field-aligned currents were detected in the data. Earth-based observations of Na, K, and Ca populations in the exosphere strongly suggest the existence of dynamic magnetospheric processes at high latitudes interacting with the planet's surface.

  • 123.
    Yamauchi, M.
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Problems on mappings of the convection and on the fluid concept1997In: Physics and Chemistry of the Earth, ISSN 00791946 (ISSN), Vol. 22, no 7-8, p. 709-714Article in journal (Refereed)
    Abstract [en]

    Mapping of electric fields and convection under ideal MHD or perfect gyro-trapping from the magnetopause to the ionosphere needs special caution, especially in critical regions such as the cusp and the boundary layer. Besides the existence of parallel electric fields which have been repeatedly pointed out by Alfvén, non-Maxwellian plasma distribution is another important factor that limits such mappings. The non-Maxwellian distribution sometimes destroy even the hydrodynamic concept of the convection. © 1997 Published by Elsevier Science Ltd.

  • 124. Yamauchi, M
    et al.
    Nilsson, H
    Eliasson, L
    Norberg, O
    Boehm, M
    Clemmons, J H
    Lepping, R P
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ohtani, S I
    Yamamoto, T
    Mukai, T
    Terasawa, T
    Kokubun, S
    Dynamic response of the cusp morphology to the solar wind: A case study during passage of the solar wind plasma cloud on February 21, 19941996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A11, p. 24675-24687Article in journal (Refereed)
    Abstract [en]

    On February 21, 1994, both Geotail and LMP 8 satellites detected an interplanetary plasma cloud with intense interplanetary magnetic field (IMF>50 nT) and high dynamic pressure (> 50 nPa). During this interval the Freja satellite detected intense cusp-like plasma injections in four out of six dayside traversals. The first two traversals are carefully studied, During the first traversal the overall morphology of the ion injection is characterized by a ''multiple-injection'' signature over a wide magnetic local time (MLT) range, whereas it is characterized by a ''single-injection'' signature with narrow injection region at 8 MLT in the second traversal, The solar wind conditions were also quite different between these two periods: while both dynamic and magnetic pressures stayed high during entire period, the dynamic beta was much higher during the first Freja traversal than during the second traversal. Between these two traversals, the cusp plasma injection is detected by the Sondre Stromfjord radar. The radar signature of the plasma injection is identified using the satellite particle data when the satellite and the radar were conjugate (the satellite's footprint was in the radar's field of view.) The cusp position and dynamics observed by the Sondre Stromfjord radar again show a very good correlation to the solar wind condition, especially to the dynamic pressure. The result indicates the following. (1) During southward IMF the cusp morphology differs for conditions of high or low solar wind dynamic pressure. High dynamic pressure widens the cusp (with multiple injections), whereas high magnetic pressure narrows it (with single injection), The effect of the IMF on the cusp locations and morphology becomes dominant only when the dynamic pressure is not very high, (2) Such a morphological difference reflects dynamic pressure more than dynamic beta during southward IMF at least during times of high solar wind dynamic pressure. (3) The cusp morphology responds very quickly to the changes in the solar wind conditions.

123 101 - 124 of 124
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