Near-Earth substorm features from multiple satellite observations

Journal of Geophysical Research 01/2008; 113(A7). DOI: 10.1029/2007JA012738
Source: OAI

ABSTRACT This paper was published as Journal of Geophysical Research, 2008, 113, A07S26. Copyright 2008 American Geophysical Union. It is available from Doi: 10.1029/2007JA012738 Metadata only entry We investigate a substorm on 3 October 2004 during which 11 satellites were located in near-Earth magnetotail (X GSM > −10 R E). Double Star 1 (TC-1), Cluster, and LANL-97 satellites were closely aligned in the dawn-dusk direction (<1 R E apart) for this conjunction. After substorm expansion onset, TC-1 observed plasma sheet thinning at X ≈ −5.5 R E and later detected signature of plasma flow shear that may be associated with an auroral arc. Analysis of the dawn-dusk magnetic perturbations from GOES-10 and Polar suggests that these could be caused by a substorm current system consisting of not only the azimuthal closure of field-aligned currents (the substorm current wedge) but also the meridional closure of field-aligned currents. The temporal sequence of substorm activity (particle injection, current disruption, and dipolarization) revealed by these satellites indicates that the substorm expansion activity was initiated close to the Earth and spread later to further downstream distances. Furthermore, TC-1 and Cluster data show that there is no close relationship between some dipolarizations and Earthward plasma flows in the near-Earth region. The overall development of substorm activity is in agreement with the near-Earth initiation model for substorms. A temporal evolution of the magnetic field reconfiguration and plasma boundary motion during this substorm is constructed from these observations.

  • [Show abstract] [Hide abstract]
    ABSTRACT: We examine a near-Earth current disruption/dipolarization (CDD) event in which two THEMIS satellites were located at nearly identical equatorial projections but separated by the distance from the neutral sheet. One satellite was very close to the neutral sheet with ∣Bx∣, ∣By∣ < 1.5 nT at CDD onset that coincided with ground signatures of substorm expansion onset. The cross-tail current density between the two satellites varied with a time scale of seconds during CDD and was reduced by ˜40% eventually. If the current density profile could be represented well by the combination of a dipole field and a one-dimensional current sheet, then the current density integrated over the current sheet thickness was reduced by only ˜12%. The difference can be attributed to plasma sheet expansion in association with CDD. There were occasional breakdowns of the frozen-in-field condition during CDD as well. The particle energization associated with CDD approached the satellite from the Earthward-dawnward direction near the neutral sheet based on the ion sounding technique, constituting compelling evidence that this near-Earth CDD arose from disturbances originating in the near-Earth region (Xgsm > -8.1 RE) and was not due to magnetic flux pileup (requiring frozen-in condition) or arrival of a dipolarization front from mid-tail (Xgsm < -15 RE) disturbances.
    Journal of Geophysical Research Atmospheres 12/2011; 116(A12):12239-. DOI:10.1029/2011JA017107 · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We examined the magnetospheric magnetic field and plasma responses to an encounter of a discontinuity in the Bx component of interplanetary magnetic field (IMF). The striking variations of simultaneous solar wind dynamic pressure and IMF-Bz were not observed. Furthermore, we found that this IMF-Bx discontinuity was a heliospheric current sheet, separating two high-speed solar wind streams with different velocity and magnetic polarity. In this study, the magnetic field and plasma data were obtained from Time History of Events and Macroscale Interactions during Substorms (THEMIS), Cluster, and GOES to investigate the magnetospheric responses, and those were taken from ACE and Geotail to monitor the solar wind conditions. Simultaneous geomagnetic field variations from the ground observatories and aurora activity from Polar were also examined. When the discontinuity encountered the magnetosphere, THEMIS-D, -E, and THEMIS-A observed abrupt and transient magnetic field and plasma variations in the dawnside near-Earth magnetotail and tail-flank magnetopause. Significant magnetic field perturbations were not observed by Cluster as located in the duskside magnetotail at this time interval. Although simultaneous dipolarization and negative bay variations with Pi2 waves were observed by GOES and the ground observatories, global auroral activities were not found. Around the dawnside tail-flank magnetopause, THEMIS-C and -A experienced the magnetopause crossings due to the magnetopause surface waves induced by Kelvin-Helmholtz instability. These results suggest that the magnetic field and plasma variations in the near-Earth magnetotail and tail-flank magnetopause were caused by moderate substorm-like phenomena and magnetopause surface waves. They also indicate that clear magnetospheric disturbances can be brought even without significant variations in the solar wind.
    Journal of Geophysical Research Atmospheres 04/2012; 117(A4):4218-. DOI:10.1029/2011JA016894 · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we investigate intense (with current density larger than 15 nA/m(2)) thin (thickness is less than proton gyroradius) horizontal current sheets observed by Cluster in 2003 year in the Earth magnetotail. We compare observed profiles of the curlometer current density with particle currents and analytical estimates. We show that intense horizontal current sheets represent a particular class of current sheets where the almost all current density can be described by electron curvature currents. Intensification of these currents is provided by increase of the electron temperature anisotropy in of current sheets where parallel/antiparallel electron beams are found. The substantial part of the vertical pressure balance in such intense sheets can be supported by the local increase of the shear component of the magnetic field. We show that this is common property for intense current sheets observed in the magnetotail and in the laboratory experiments. The later measurements can help in understanding particular details, since spacecraft observations of such current sheets are relatively rare, especially due to their relation to localized active regions.
    06/2013; 118(6-6):2789-2799. DOI:10.1002/jgra.50297