Flux transfer events produced by bursty merging at a single X line

Abstract

We present predictions for the signatures of flux transfer events (FTEs) at the dayside magnetopause produced by bursty merging at a single extended X line. In this MHD model, the time‐dependent enhanced local resistivity turns on at a low northern latitude for a brief time and then turns off. Realistic ratios of magnetosheath to magnetosphere parameters are chosen to conform with observations and our previous simulations [Ku and Sibeck, 1997, 1998]: ρmsh/ρsph = 10, Bmsh/Bsph = 0.5, and Tmsh/Tsph = 0.175. The burst of merging produces FTEs marked by strongly asymmetric bipolar magnetic field and plasma velocities normal to the magnetopause in the magnetosheath and no significant signatures in the magnetosphere, just as in the previously studied case for the step‐function onset of merging [Ku and Sibeck, 1997]. However, the simulation produces other FTE signatures that differ strikingly from those generated by the step‐function onset of merging. After the resistivity is switched off, one or more secondary reconnection sites appear on the trailing edge of the events. Merging at these sites inflates and propels the main FTE as it moves out of the simulation domain. Merging at these sites also fills a magnetic island with hot tenuous plasma near the subsolar (symmetry) point. Transient magnetic islands form on the trailing edge of the main FTE, but these remain small and may disappear. Scatterplots of various parameters versus the plasma density reveal that steep changes for the temperature kT, magnetic field BZ, and the Alfvén velocity occur on the magnetosheath side immediately adjacent to the magnetopause and also reflect the fact that the events scarcely deform the magnetopause.