Kinetic processes in the plasma sheet observed during auroral activity
Fillingim, Matthew Owen
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In this dissertation we analyze plasma sheet magnetic field and plasma data observed during varying levels of auroral activity from very small, isolated events known as pseudobreakups to large, global events known as substorms. The plasma and magnetic field data are taken from instruments onboard the WIND spacecraft while it traverses the near-Earth plasma sheet. Simultaneous global auroral images from POLAR/UVI allow us to determine the auroral activity level. The goal of this dissertation is to provide the most complete set of plasma sheet observations during auroral activity currently available. The kinetic aspects of the plasma dynamics which have largely been ingnored in other works are emphasized here. We have the capability to resolve changes in the three dimensional ion distribution functions with a time resolution comparable to or faster than the local ion gyroperiod. In addition, we consider the typically neglected electron dynamics when relating plasma sheet processes to the aurora. We find that the plasma sheet signatures of both pseudobreakups and substorms appear very similar. During both types of events, increases in auroral precipitation into the ionosphere are associated with large amplitude, high frequency magnetic field fluctuations, large Earthward ion 〈 v〉, increases in the fluxes of high energy ions and electrons, and hardening of the electron spectrum. Both ion and electron distributions appear to be composed of multiple components. Electromagnetic waves with power at frequencies up to and above the local proton gyrofrequency area also observed. Additionally, the ion distributions can change significantly in one gyroperiod. Together, these results imply that the microphysical processes occurring in the plasma sheet during pseudobreakups and substorms are the same and that kinetic effects are important. Therefore, magnetohydrodynamics (MHD) cannot adequately describe the physics occurring during large ion 〈 v〉 events.
- Geophysics