Internal structure of flux transfer events produced by the onset of merging at a single X line

Abstract

Abstract. We present a new, higher-order, two-dimensional, magnetohydrodynamic model for the detailed internal structure of bubbles produced by the onset of merging along a single subsolar X line. The key feature of the model is to implement a nonlinear filter to postprocess results provided by the pseudospectral element method. The devised nonlinear filter (1) eliminates only the high-frequency oscillations, (2) retains conservation laws, and (3) enforces a total variation diminished criterion to guarantee the elimination of spurious oscillations near discontinuities. For realistic parameters, the model predicts that satellites which remain in the magnetosheath will observe asymmetric bipolar magnetic field signatures normal to the magnetopause, magnetic field strength increases, density and temperature decreases, and velocities opposite the motion of the events. Satellites in the magnetosheath which enter the events observe asymmetric bipolar signatures normal to the magnetopause, magnetic field strength decreases, densities intermediate between those in the magnetosheath and magnetosphere, temperature increases, and velocities in the direction of event motion. Satellites initially located just outside the the magnetopause observe greatly depressed densities and enhanced temperatures (but no significant bipolar signatures normal to the magnetopause) followed by velocity jets of magnetosheath-like plasma on northward magnetospheric magnetic field lines. Satellites in the magnetosphere which enter the events observe depressed magnetic field strengths, enhanced densities and temperatures, and accelerated flows surrounding a core region of accelerated magnetosheath-like plasma. Neither they nor satellites which remain in the magnetosphere observe any significant bipolar signatures normal to the nominal magnetopause.

Flux transfer events produced by the onset of merging at multiple X lines

“…The retention of BV ß B was discussed in great detail by Ku and Sibeck [1997] and need not be addressed here. The initial conditions are identical to those used in the paper of Sibeck [1997, 1998a], who assumed that initial values for all the variables, including the field strength, the plasma density, and the background magnetosheath flow (when present), vary linearly (or smoothly) from the magnetosheath to the magnetosphere across the magnetopause current layer.…”

“…Next, a nonlinear filter [Ku and Sibeck, 1997] is used to postprocess the results pro-vided by the high-order dispersive pseudospectral element method to capture the sharp gradients that occur at shock waves, contact discontinuities, and thin boundary layers.…”

Three‐dimensional MHD simulation of FTEs produced by merging at an isolated point in a sheared magnetic field configuration

“…Transient magnetic islands also form on the trailing edge of the main FTE, forming secondary FTEs, but they remain small and later disappear. Besides giving important information about FTE evolution and the associated perturbation in the ambient plasma and magnetic field, the 2-D simulations performed in Ku and Sibeck [1997, 1998a, 1998b, 2000 only consider perfectly antiparallel fields, a particular case that is rarely observed at the magnetopause. Also, in their 2-D simulations the FTE evolution is restricted to the plane perpendicular to the magnetopause as well as the evolution of associated perturbations.…”

“…However, they do not discuss the mechanism responsible for the increase in viscosity close to the FTE nor investigate the evolution of magnetic field and plasma inside the FTE. Ku and Sibeck [1997, 1998a, 1998b, 2000 performed a series of 2-D magnetohydrodynamic (MHD) simulations to investigate the signatures of FTEs produced by a Petschek-type reconnection occurring close to the subsolar point. In their first work [Ku and Sibeck, 1997] reconnection is started by a step function timedependent localized increase in resistivity.…”

“…Ku and Sibeck [1997, 1998a, 1998b, 2000 performed a series of 2-D magnetohydrodynamic (MHD) simulations to investigate the signatures of FTEs produced by a Petschek-type reconnection occurring close to the subsolar point. In their first work [Ku and Sibeck, 1997] reconnection is started by a step function timedependent localized increase in resistivity. The plasma is at rest at the beginning of the simulation, and the initial magnetosheath and magnetosphere field and plasma parameters are chosen in a way to reproduce realistic ratios observed by satellites for the magnetosheath-magnetosphere system.…”