The effect of different resistivity models on magnetotail dynamics

Abstract

Two-dimensional, time-dependent MHD simulations of the interaction between the solar wind and the earth's magnetosphere have been performed to study magnetotail dynamics with varying forms of anomalous resistivity. In general, the resulting models conform to the neutral line model proposed for substorms with near-earth x points and high-speed tailward flows occurring in the magnetotail. However, in the case where Joule heating is included in the physical description of the system, the near-earth x point never moves far down tail, and high-speed tailward flows never stop. Only in the case where there is no Joule heating does the x point move down tail. Simultaneously, the high-speed tailward flows cease. These results indicate that the mechanism of energy dissipation can have an important effect on reconnection processes and the global magnetospheric dynamics.

Semirelativistic Magnetohydrodynamics and Physics-Based Convergence Acceleration

“…This approximation is very convenient and easy to implement in numerical codes. It is extensively used in global magnetospheric codes to avoid unphysical Alfvén speed (V A > c) and for increasing the explicit time step (with reduced values of c) [13]. We note, however, that (40) suffers from two shortcomings: it cannot be put in a conservation form, which would be important in obtaining discontinuous solutions, and the steady-state solution depends on the value of the reduced speed of light.…”

“…Another type of approximation uses the primitive nonconservative form of the MHD equations and multiplies the Lorentz force j × B by a factor γ 2 A . This form has been used for many years, for both steady state and time accurate applications (e.g., [13,18,23]), although in this case the steady state is not independent of the speed of light. We will examine the wave speeds and the stability of these simplified forms of the semirelativistic MHD equations as well.…”

Coupling of a global MHD code and an inner magnetospheric model: Initial results

“…Small-scale, non-MHD plasma processes play an important role in the dynamics of the region, notably by magnetic reconnection and auroral particle acceleration, but these occur in limited regions. Though other techniques are being developed [e.g., Nishikawa, 2001;Delamere et al, 2001], global MHD codes represent the state-of-the-art in theoretical representation of the outer magnetosphere [e.g., Ogino and Walker, 1984;Lyon et al, 1986;Winglee, 1994;Raeder et al, 1995;Tanaka, 1995;Janhunen, 1996;White et al, 1998;Powell et al, 1999].…”

Anisotropy Reversals in the Distant Magnetotail and Their Association with Magnetospheric Substorms

“…In that scenario a series of southward to northward turnings of the solar wind magnetic field may be responsible for the occurrence of tailward-then-Earthward-flow sequences in the magnetotail and their association with substorms. Since we know that northward IMF turnings axe responsible for triggering substorms in most cases of isolated substorm occurrences (McPherron et al, 1986;Dmitrieva and Sergeev, 1983;Lyons et al, 1995) and are also related with a tailward retreat of a neutral line seen in global MHD simulations (Lyon et al, 1986;Ogino et al, 1994) it is possible that such northward turnings were responsible for the reversals of the flow from tailward to Earthward at GEOTAIL. In this case the reversals would bear no relationship to the southward turning but would be time-locked (with some time delay) to a northward turning of the IMF.…”