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Sökning: WFRF:(Apatenkov S. V.)

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  • Angelopoulos, V., et al. (författare)
  • First Results from the THEMIS Mission
  • 2008
  • Ingår i: Space Science Reviews. - 0038-6308 .- 1572-9672. ; 141:1-4, s. 453-476
  • Forskningsöversikt (refereegranskat)abstract
    • THEMIS was launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. During the first seven months of the mission the five satellites coasted near their injection orbit to avoid differential precession in anticipation of orbit placement, which started in September 2007 and led to a commencement of the baseline mission in December 2007. During the coast phase the probes were put into a string-of-pearls configuration at 100 s of km to 2 R-E along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007. THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents. These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.
  • 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.
  • Sergeev, V. A., et al. (författare)
  • Substorm-Related Near-Earth Reconnection Surge : Combining Telescopic and Microscopic Views
  • 2019
  • Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 46:12, s. 6239-6247
  • Tidskriftsartikel (refereegranskat)abstract
    • A strong similar to 11-min-long surge of the lobe reconnection was observed during a substorm on the tailward side of the near-Earth neutral line. In the southern lobe near the reconnection separatrix the MMS spacecraft observed short-duration earthward electron beams providing the local Hall current, tailward propagating Alfven wave (AW) bursts with Poynting flux up to 10(-4) W/m(2), and large-amplitude E field spikes (e-holes) and low hybrid waves. The reconnection surge was accompanied by substorm current wedge formation and fast poleward expansion of auroral bulge-related westward electrojet in the conjugate ionosphere. During its meridional crossing above the expanding bulge the Metop-2 spacecraft observed an intense energetic precipitation spike near the expected X line foot point and confirmed the dipolarized character of magnetic field lines inside of the bulge. Globally the observed average reconnection rate ( similar to 3.3 mV/m) was sufficient to produce the magnetic flux increase in the bulge, associated with observed fast poleward expansion (about 6 degrees latitude in 5 min). Plain Language Summary Although magnetic reconnection in the magnetotail has been proposed to be the core process for the strong global magnetospheric reconfiguration and for huge particle acceleration during magnetospheric substorms, this association is mostly based on indirect evidence, because reconnection intermittently activates in different parts of the tail current sheet, and it is difficult to monitor its location and intensity variations based on direct spacecraft observations. On 28 July 2017 the MMS spacecraft succeeded in staying in the magnetotail near the active reconnection separatrix for a relatively long time during the surge of reconnection. At the same time the electric currents were enhanced and moved poleward in the magnetically conjugate part of the ionosphere, indicating configurational changes in the magnetotail. At the same minute the Metop-2 spacecraft in low-Earth orbit passed above this region and detected precipitating electrons of different energies as well as their distribution in the loss cone, which yielded conclusions about the strength of the equatorial magnetic field in the reconnected flux tubes. This unprecedented combination of conjugate observations allows us to confirm directly the important global consequences of an intense near-Earth reconnection event, which have been suggested in the near-Earth neutral line substorm scenario but could not be previously observed together in the same event.
  • 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.
  • Nakamura, R., et al. (författare)
  • Flow bouncing and electron injection observed by Cluster
  • 2013
  • Ingår i: Journal of Geophysical Research-Space Physics. - 2169-9380. ; 118:5, s. 2055-2072
  • Tidskriftsartikel (refereegranskat)abstract
    • Characteristics of particles and fields in the flow-bouncing region are studied based on multipoint observations from Cluster located at 13-15R(E) downtail during a substorm event around 12:50 UT on 7 September 2007. The Cluster spacecraft were separated by a distance of up to 10,000 km and allowed to determine the mesoscale evolution of the current sheet as well as the development of the dipolarization front. We show that the flow bouncing took place associated with a tailward-directed j x B force in a disturbed current sheet in addition to an enhanced tailward pressure gradient force. Multiple Earthward propagating dipolarization fronts accompanied by enhanced flux of energetic electrons were observed before the flow bouncing. The sequence of events started with a localized dipolarization front and ended with a large scale (>10R(E)) dipolarization front accompanied by a major increase in energetic electrons at all spacecraft and immediately followed by flow bouncing. Multiple dipolarization fronts result in the formation of compressed magnetic field with a plasma bulge bounded by thin ion-scale current layers, a favorable condition for flow bouncing. These observations suggest that to understand the flow bouncing and related acceleration of plasma in the near-Earth tail, both the large-scale MHD properties and the transient and small-scale effect of the plasma interaction with the Earth-dipole field need to be taken into account.
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