Magnetotail dynamics: MHD simulations of driven and spontaneous dynamic changes

Conference · Sun May 01 04:00:00 EDT 1994

OSTI ID:10150080

Birn, J ^[1]; Schindler, K ^[2]; Hesse, M ^[3]

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1. Los Alamos National Lab., NM (United States)
2. Ruhr-Univ., Bochum (Germany). Theoretische Phyick IV
3. National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center

The dynamic evolution of the magnetotail during growth phase and expansion phase of a substorm is studied through threedimensional time-dependent MHD simulations. To model growth phase effects, an external electric field with an equatorward inflow is applied at the boundaries over a finite time period. This leads to the formation of a thin current sheet with greatly enhanced current density in the near tail, embedded in the wider plasma/current sheet, which becomes diminished in strength. A faster, spontaneous current sheet formation occurs when entropy conservation is released in an isobaric model, while the ideal MHD constraint persists. This may be a suitable model for the late, explosive part of the growth phase. The transition to the substorm expansive phase is modeled by an increase in anomalous resistivity, using either uniform resistivity or a current density dependent resistivity which is turned on when the current density exceeds a certain threshold. In both cases the violation of ideal MHD leads to resistive instability and the formation of a near-Earth neutral line, fast flow, and plasmoid ejection, together with the dipolarization and current reduction in the region further earthward. The spontaneous increase in total region 1 type field-aligned currents associated with the disruptions of the thin current sheets is less significant than that found in earlier simulations of the disruption of a wider current sheet, whereas the driven increase in the region 1 type current is substantial. The results demonstrate that the same dynamic process which appears spontaneous in the behavior of some quantities might be interpreted as entirely driven from the observation of others.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States); National Aeronautics and Space Administration, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 10150080
• Report Number(s): LA-UR--94-1455; CONF-9403116--1; ON: DE94011702
• Country of Publication: United States
• Language: English

Related Subjects

661320
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COMPUTERIZED SIMULATION
DYNAMICS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MAGNETOTAIL
PLASMA INSTABILITY
TIME DEPENDENCE