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Sökning: WFRF:(Ganushkina N.)

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  • 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.
  • Dimmock, Andrew P., et al. (författare)
  • Direct evidence of nonstationary collisionless shocks in space plasmas
  • 2019
  • Ingår i: ; 5:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.
  • Grigorenko, E. E., et al. (författare)
  • Intense Current Structures Observed at Electron Kinetic Scales in the Near-Earth Magnetotail During Dipolarization and Substorm Current Wedge Formation
  • 2018
  • Ingår i: ; 45:2, s. 602-611
  • Tidskriftsartikel (refereegranskat)abstract
    • We use data from the 2013-2014 Cluster Inner Magnetosphere Campaign, with its uniquely small spacecraft separations (less than or equal to electron inertia length, lambda(e)), to study multiscale magnetic structures in 14 substorm-related prolonged dipolarizations in the near-Earth magnetotail. Three time scales of dipolarization are identified: (i) a prolonged growth of the B-Z component with duration <= 20 min; (ii) B-Z pulses with durations <= 1 min during the B-Z growth; and (iii) strong magnetic field gradients with durations <= 2 s during the dipolarization growth. The values of these gradients observed at electron scales are several dozen times larger than the corresponding values of magnetic gradients simultaneously detected at ion scales. These nonlinear features in magnetic field gradients denote the formation of intense and localized (approximately a few lambda(e)) current structures during the dipolarization and substorm current wedge formation. These observations highlight the importance of electron scale processes in the formation of a 3-D substorm current system.
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