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Sökning: WFRF:(Runov A.) > Sauvaud J. A.

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1.
  • Apatenkov, S. V., et al. (författare)
  • Conjugate observation of sharp dynamical boundary in the inner magnetosphere by Cluster and DMSP spacecraft and ground network
  • 2008
  • Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 26:9, s. 2771-2780
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate an unusual sharp boundary separating two plasma populations (inner magnetospheric plasma with high fluxes of energetic particles and plasma sheet) observed by the Cluster quartet near its perigee on 16 December 2003. Cluster was in a pearl-on-string configuration at 05:00 MLT and mapped along magnetic field lines to similar to 8-9 R-E in the equatorial plane. It was conjugate to the MIRACLE network and the DMSP F16 spacecraft passed close to Cluster footpoint. The properties of the sharp boundary, repeatedly crossed 7 times by five spacecraft during similar to 10 min, are: (1) upward FAC sheet at the boundary with similar to 30 nA/m(2) current density at Cluster and similar to 2000 nA/m(2) at DMSP; (2) the boundary had an embedded layered structure with different thickness scales, the electron population transition was at similar to 20 km scale at Cluster (<7 km at DMSP), proton population had a scale similar to 100 km, while the FAC sheet thickness was estimated to be similar to 500 km at Cluster (similar to 100 km at DMSP); (3) the boundary propagated in the earthward-eastward direction at similar to 8 km/s in situ (equatorward-eastward similar to 0.8 km/s in ionosphere), and then decelerated and/or stopped. We discuss the boundary formation by the collision of two different plasmas which may include dynamical three-dimensional field-aligned current loops.
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2.
  • Apatenkov, S. V., et al. (författare)
  • Multi-spacecraft observation of plasma dipolarization/injection in the inner magnetosphere
  • 2007
  • Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 25:3, s. 801-814
  • Tidskriftsartikel (refereegranskat)abstract
    • Addressing the origin of the energetic particle injections into the inner magnetosphere, we investigate the 23 February 2004 substorm using a favorable constellation of four Cluster (near perigee), LANL and Geotail spacecraft. Both an energy-dispersed and a dispersionless injection were observed by Cluster crossing the plasma sheet horn, which mapped to 9-12 R-E in the equatorial plane close to the midnight meridian. Two associated narrow equatorward auroral tongues/streamers propagating from the oval poleward boundary could be discerned in the global images obtained by IMAGE/WIC. As compared to the energy-dispersed event, the dispersionless injection front has important distinctions consequently repeated at 4 spacecraft: a simultaneous increase in electron fluxes at energies similar to 1.300 keV, similar to 25 nT increase in B-Z and a local increase by a factor 1.5-1.7 in plasma pressure. The injected plasma was primarily of solar wind origin. We evaluated the change in the injected flux tube configuration during the dipolarization by fitting flux increases observed by the PEACE and RAPID instruments, assuming adiabatic heating and the Liouville theorem. Mapping the locations of the injection front detected by the four spacecraft to the equatorial plane, we estimated the injection front thickness to be similar to 1 R-E and the earthward propagation speed to be similar to 200-400km/s (at 9-12 RE). Based on observed injection properties, we suggest that it is the underpopulated flux tubes (bubbles with enhanced magnetic field and sharp inner front propagating earthward), which accelerate and transport particles into the strong-field dipolar region.
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3.
  • Baumjohann, W., et al. (författare)
  • Dynamics of thin current sheets : Cluster observations
  • 2007
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 25:6, s. 1365-1389
  • Forskningsöversikt (refereegranskat)abstract
    • The paper tries to sort out the specific signatures of the Near Earth Neutral Line (NENL) and the Current Disruption (CD) models. and looks for these signatures in Cluster data from two events. For both events transient magnetic si-natures are observed, together with fast ion flows. In the simplest form of NENL scenario, with a large-scale two-dimensional reconnection site, quasi-invariance along Y is expected. Thus the magnetic signatures in the S/C frame are interpreted as relative motions, along the X or Z direction, of a quasi-steady X-line, with respect to the S/C. In the simplest form of CD scenario an azimuthal modulation is expected. Hence the signatures in the S/C frame are interpreted as signatures of azimuthally (along Y) moving current system associated with low frequency fluctuations of J(y) and the corresponding field-aligned currents Event I covers a pseudo-breakup, developing only at high latitudes. First, a thin (H approximate to 2000Km approximate to 2 rho(i), with pi the ion gyroradius) Current Sheet (CS) is found to be quiet. A slightly thinner CS (H approximate to 1000-2000 km approximate to 1-2 rho(i)), crossed about 30 min later, is found to be active. with fast earthward ion flow bursts (300-600 km/s) and simultaneous large amplitude fluctuations (delta B/B similar to 1). In the quiet CS the current density J(y) is carried by ions. Conversely, in the active CS ions are moving eastward; the westward current is carried by electrons that move eastward, faster than ions. Similarly, the velocity of earthward flows (300-600 km/s), observed during the active period. maximizes near or at the CS center. During the active phase of Event I no signature of the crossing of an X-line is identified, but an X-line located beyond Cluster could account for the observed ion flows, provided that it is active for at least 20 min. Ion flow bursts can also be due to CD and to the corresponding dipolarizations which are associated with changes in the current density. Yet their durations are shorter than the duration of the active period. While the overall partial derivative Bz/partial derivative t is too weak to accelerate ions up to the observed velocities, short duration partial derivative B-z/partial derivative t can produce the azimuthal electric field requested to account for the observed ion flow bursts. The corresponding large amplitude perturbations are shown to move eastward. which suggests that the reduction in the tail current could be achieved via a series of eastward traveling partial dipolarisations/CD. The second event is much more active than the first one. The observed flapping of the CS corresponds to an azimuthally propagating wave. A reversal in the proton flow velocity, from 1000 to + 1000 km/s, is measured by CODIF. The overall flow reversal, the associated change in the sign of B-z and the relationship between B-x and B-y suggest that the spacecraft are moving with respect to an X-line and its associated Hall-structure. Yet, a simple tailward retreat of a large-scale X-line cannot account for all the observations, since several flow reversals are observed. These quasi-periodic flow reversals can also be associated with an azimuthal motion of the low frequency oscillations. Indeed, at the beginning of the interval B-y varies rapidly along the Y direction; the magnetic signature is three-dimensional and essentially corresponds to a structure of filamentary field-aligned current, moving eastward at similar to 200 km/s. The transverse size of the structure is similar to 1000 km. Similar structures are observed before and after. Thesefilamentary structures are consistent with an eastward propagation of an azimuthal modulation associated with a current system J(y), J(x). During Event 1, signatures of filamentary field-aligned current structures are also observed, in association with modulations of J(y). Hence, for both events the structure of the magnetic fields and currents is three-dimensional.
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