ABSTRACT

The magnetospheric substorm constitutes the largest energy dissipation process in the magnetosphere, and the explication of the nature of substorm onset is the key to understanding the complex dynamics of the magnetotail. Preliminary 3-D particle-in-cell (PIC) simulations have suggested that an interchange mode driven by a positive tailward gradient in the equatorial magnetic field may be the underlying mechanism for triggering substorms. This mode is driven by the need to return magnetic flux to the dayside region; since this flux transfer must occur over large scales in the magnetotail, the Bz interchange is potentially a stronger and more dynamic instability than the standard interchange. This project will carry out a detailed, fully kinetic investigation of ballooning/interchange modes in configurations characteristic of the coupled magnetosphere-ionosphere system. The primary tool will be state-of-the-art, large-scale, 3-D PIC simulations carried out on massively parallel computers. These new simulations will overcome the previous limitations associated with a small ion to electron mass ratio, limited spatial extent in the east-west direction, and a too strong convection electric field. The conditions that lead to growth, the saturation mechanism and level, and the effect of ionospheric boundary conditions will be determined. The simulations will also determine whether or not an external trigger such as a northward turning of the IMF can directly excite the nonlinear interchange. It is possible that both types of interchange may occur simultaneously. This could lead to the creation of a magnetic neutral region magnetic reconnection can take place under the continued driving by the convection electric field. The project will provide a decisive determination of whether the interchange mode scenario is a viable solution to the substorm onset conundrum. The project will provide training for a graduate student in the rapidly evolving field of computational plasma physics. In addition, the research personnel will collaborate with the Los Angeles Physics Teachers Alliance Group (LAPTAG) to develop an outreach presentation on the use of computers in scientific research. This presentation, to be offered on several Saturdays during the year, will aim at demonstrating to local high school students the exciting opportunities in science made possible by advances in computing power and encouraging them to further their education in science.

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