Investigation of global periodic sawtooth oscillations observed in energetic particle flux at geosynchronous orbit.

Abstract

Sawtooth events are defined as quasi-periodic, large-amplitude particle flux oscillations with a periodicity about 2-4 hours observed by geosynchronous Los Alamos National Laboratory satellites. In this thesis, the periodicity of sawtooth events is examined statistically first. As each oscillation shows similar signatures with isolated magnetospheric substorms, there are different opinions about whether sawtooth events are just an intense periodic form of magnetospheric substorms or they are a different magnetospheric activity due to their global and quasi-periodic characters. To help answer this, we use 96 sawtooth events intervals, including 394 individual teeth, and 213 isolated magnetospheric substorms to statistically analyze the similarities and differences in the ground geomagnetic disturbance, plasma property and magnetic dipolarization at geosynchronous orbit between the two categories. We also examine the relationship between sawtooth events and other magnetosphere phenomena, i.e., steady magnetospheric convection events and magnetic storms. Further we investigate the solar wind driver conditions during sawtooth events to understand why the Earth's magnetosphere prefer sawtooth event mode than magnetospheric substorms and other magnetosphere phenomena.