Thin current sheet in the substorm late growth phase: Modeling of THEMIS observations

[1] The structure of a thin current sheet prior to the expansion onset of a substorm event that occurred on 26 February 2008 is studied in the near-Earth magnetotail on the basis of Time History of Events and Macroscale Interactions During Substorms (THEMIS) observations. During this time interval, the ion distribution showed mushroom-shaped structures with clear nongyrotropic features, indicating that the warmer component of the ions was unmagnetized, which becomes possible only if the gyroradii of these ions are comparable with the current sheet thickness. By comparing the observations with the model proposed by Sitnov et al. (2003), which is a modification of the Harris (1962) model by considering the effect of the meandering ions in thin current sheets, we reconstruct the current sheet structure in the late growth phase of the substorm. Warmer ions, mostly following meandering orbits across the neutral sheet, are found to remarkably alter the current sheet profiles and therefore play an important role in the formation of the thin current sheet.

[1]  R. Abiad,et al.  The THEMIS ESA Plasma Instrument and In-flight Calibration , 2008 .

[2]  I. J. Rae,et al.  Tail Reconnection Triggering Substorm Onset , 2008, Science.

[3]  Wolfgang Baumjohann,et al.  Observations of an active thin current sheet , 2008 .

[4]  Werner Magnes,et al.  The THEMIS Fluxgate Magnetometer , 2008 .

[5]  Vassilis Angelopoulos,et al.  The THEMIS Mission , 2008 .

[6]  H. Malova,et al.  Marginal stability of thin current sheets in the Earth's magnetotail , 2008 .

[7]  Wolfgang Baumjohann,et al.  Dynamics of thin current sheets: Cluster observations , 2007 .

[8]  Q. Zong,et al.  Energy filter effect for solar wind particle entry to the plasma sheet via flank regions during southward interplanetary magnetic field , 2007 .

[9]  Eric Ronald Priest,et al.  Reconnection of magnetic fields : magnetohydrodynamics and collisionless theory and observations , 2007 .

[10]  Parvez N. Guzdar,et al.  Structure and dynamics of a new class of thin current sheets , 2006 .

[11]  Enrico Camporeale,et al.  Model of bifurcated current sheets in the Earth's magnetotail: Equilibrium and stability , 2005 .

[12]  Wolfgang Baumjohann,et al.  Electric current and magnetic field geometry in flapping magnetotail current sheets , 2005 .

[13]  Wolfgang Baumjohann,et al.  How typical are atypical current sheets? , 2005 .

[14]  P. Louarn,et al.  Bifurcated current sheet: model and Cluster observations , 2005 .

[15]  J. Sauvaud,et al.  Cluster observations of velocity space‐restricted ion distributions near the plasma sheet , 2004 .

[16]  A. Lui,et al.  Model of ion‐ or electron‐dominated current sheet , 2004 .

[17]  G. Parks,et al.  Modeling of remote sensing of thin current sheet , 2004 .

[18]  B. Rogers,et al.  A model of the bifurcated current sheet: 2. Flapping motions , 2004 .

[19]  H. Hayakawa,et al.  Statistical study of thin current sheet evolution around substorm onset , 2004 .

[20]  J. Birn,et al.  Thin electron current sheets and their relation to auroral potentials , 2004 .

[21]  M. Sitnov,et al.  A model of the bifurcated current sheet , 2003 .

[22]  F. Mottez.  Exact nonlinear analytic Vlasov-Maxwell tangential equilibria with arbitrary density and temperature profiles , 2003 .

[23]  Rumi Nakamura,et al.  Cluster observation of a bifurcated current sheet , 2003 .

[24]  J. Birn,et al.  Models of two‐dimensional embedded thin current sheets from Vlasov theory , 2001 .

[25]  H. Malova,et al.  Thin and superthin ion current sheets. Quasi-adiabatic and nonadiabatic models , 2000 .

[26]  W. Daughton.  The unstable eigenmodes of a neutral sheet , 1999 .

[27]  T. Mukai,et al.  Ion dynamics in magnetic reconnection: Comparison between numerical simulation and Geotail observations , 1998 .

[28]  A. Khrabrov,et al.  DeHoffmann-Teller Analysis , 1998 .

[29]  K. Glassmeier,et al.  Relation of Magnetic Field Line Reconnection and Unstable Nongyrotropic Particle Distributions , 1998 .

[30]  Patrick W. Daly,et al.  7 - Multi-Spacecraft Analysis of Plasma Kinetics , 1998 .

[31]  H. Malova,et al.  Self-consistent structure of a thin anisotropic current sheet , 1997 .

[32]  Christopher T. Russell,et al.  Structure of the tail plasma/current sheet at ∼11 RE and its changes in the course of a substorm , 1993 .

[33]  C. Russell,et al.  Current carriers in the near-earth cross-tail current sheet during substorm growth phase , 1990 .

[34]  Lev M. Zelenyi,et al.  Regular and chaotic charged particle motion in magnetotaillike field reversals: 1. Basic theory of trapped motion , 1989 .

[35]  René Pellat,et al.  Stability of a thick two‐dimensional quasineutral sheet , 1982 .

[36]  S. Cowley.  The effect of pressure anisotropy on the equilibrium structure of magnetic current sheets , 1978 .

[37]  P. Channell.  Exact Vlasov–Maxwell equilibria with sheared magnetic fields , 1976 .

[38]  R. Pellat,et al.  Magnetic merging in collisionless plasmas , 1976 .

[39]  K. Schindler.  A SELF-CONSISTENT THEORY OF THE TAIL OF THE MAGNETOSPHERE , 1972 .

[40]  B. Sonnerup.  Adiabatic particle orbits in a magnetic null sheet , 1971 .

[41]  T. Speiser.  Particle trajectories in model current sheets: 1. Analytical solutions , 1965 .

[42]  E. G. Harris.  On a plasma sheath separating regions of oppositely directed magnetic field , 1962 .