Three-dimensional MHD modeling of magnetotail dynamics for different polytropic indices

Journal Article · Wed Apr 01 04:00:00 EST 1992 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA03003· OSTI ID:5398084

Hesse, M; Birn, J ^[1]

---

1. Los Alamos National Lab., NM (United States)

The evolution of the three-dimensional resistive tearing instability in a magnetotail configuration is analyzed by means of a resistive MHD code for various forms of the energy equation including ohmic and compressional heating. The following study emphasizes the changes in magnetotail evolution brought about by variation of the assumed value of the polytropic exponent {gamma}, representing the ratio of specific heats in the energy equation, which closes the set of MHD equations. The authors find that within the range of 2/3 {le} {gamma} {le} 4, a tearing mode develops in all cases. Certain properties, such as the formation and ejection of a plasmoid, associated with the formation of the reversal region of the north-south component of the magnetic field, and strong earthward and tailward flow fields prevail as qualitative features independent of the value of {gamma} chosen. Quantitatively, however, magnetotail evolution can be quite different for different values of {gamma}. This is found primarily in the evolution of the temperature, where they find heating by a factor of order two with higher temperatures for higher values of {gamma}. This is combined with a density reduction by a similar factor. Both features are consistent recent observational results from a superposed epoch analysis of 39 substorm events in the near tail. Ohmic dissipation is found to be the major source of the heating, while adiabatic or nonadiabatic compression may contribute primarily in the closed field region earthward of the reconnection site. Furthermore, quantitative values of typical flow speeds and evolution time scales show some dependence on the polytropic index.

• OSTI ID: 5398084
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 97:A4; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
FLUID MECHANICS
HEATING
HYDRODYNAMICS
INSTABILITY
MAGNETIC BAYS
MAGNETOHYDRODYNAMICS
MAGNETOTAIL
MATHEMATICAL MODELS
MECHANICS
PHYSICAL PROPERTIES
PLASMA DENSITY
PLASMA HEATING
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA SHEET
PLASMOIDS
SPECIFIC HEAT
TEARING INSTABILITY
THERMODYNAMIC PROPERTIES
THREE-DIMENSIONAL CALCULATIONS
VARIATIONS