HR: 14:50h
AN: SM53C-03 INVITED     [Abstracts]
TI: Does the Hall effect solve the flux pileup saturation problem?
AU: * Dorelli, J C
EM: john.dorelli@unh.edu
AF: University of New Hampshire, Space Science Center, Morse 245E 39 College Road, Durham, NH 03801, United States
AB: Previous analytic work on the theory of resistive Hall MHD magnetic reconnection suggests that Hall electric fields can mitigate the well known flux pileup saturation problem [Dorelli, J. C., Phys. Plasmas, 10, 3309, 2003.]. Specifically, the decoupling of electron and ion bulk velocities within the ion inertial region causes flux pileup to saturate (in the limit of vanishing resistivity) before the reconnection rate begins to drop; the reconnection rate becomes insensitive to the resistivity, but it depends strongly on the ion inertial length. The physics of pileup saturation in the Hall limit is straightforward: strong electron flows (associated with the out- of-plane quadrupole magnetic field structure) drive fast reconnection within the ion inertial region without piling up magnetic energy upstream of the current sheet. As the resistivity is decreased, the electron flow (and out-of-plane magnetic field) increases to accommodate the externally imposed reconnection rate. Recently, Craig and Watson [Phys. Plasmas, 12, 012306, 2005.] have argued that the increase of the out-of-plane field poses a new saturation problem, since the field cannot increase without limit. In this presentation, we demonstrate that this new saturation effect is an artifact of the analytic pileup solutions, in which the out-of-plane field blows up at infinity. In reality, the out-of-plane field vanishes at infinity (in the ideal MHD region of the solution), so that the analytic solutions are only relevant near the X line. We use resistive Hall MHD simulations to demonstrate that the amplitude of the out-of-plane field remains bounded (though the first derivative increases) as the resitivity is decreased. We conclude that the Hall effect mitigates the flux pileup saturation problem, allowing fast reconnection to occur in macroscopic thin current sheets.
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2724 Magnetopause and boundary layers
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly