Abstract
The magnetosphere is the region of space dominated by the Earth’s magnetic field. The expanding outer atmosphere of the Sun, the solar wind, compresses the magnetosphere on the dayside and extends it hundreds of Earth radii (RE) in a comet-like tail on the nightside. The solar wind drives transport within the magnetosphere and in the ionosphere through the process of reconnection between the interplanetary magnetic field and the Earth’s magnetic field. Magnetospheric physics uses a variety of modeling and simulation techniques including global magnetohydrodynamic (MHD) simulations of the entire solar wind, magnetosphere and ionosphere system, large-scale kinetic (LSK) simulations of the dynamics of charged particles in the magnetosphere and particle and cell (PIC) simulations of plasma and wave processes.
We will demonstrate how magnetospheric structure and dynamics can be studied by using a combination of spacecraft observations and these theoretical simulation techniques. We will concentrate on a specific example based on observations from the Cluster mission. Specifically, plasma observations at the outer edge of the plasma sheet, called the plasma sheet boundary layer (PSBL), observed by the four Cluster spacecraft show energy-dispersed structures in which the highest energy ions are observed nearest the boundary with lower energy particles nearer the central part of the plasma sheet. We show that these particles originate from non-adiabatic motion in a region of the equatorial plasma sheet just earthward of a magnetic neutral line in the tail. We call this region the “stochastic sea”. Finally we analyze the stability of observed ion shell distributions to explain observations of ion cyclotron waves. Thus the combination of Cluster data and simulations allows us to illuminate the physics at work in the Earth’s magnetosphere.