Upflowing auroral ion conics observed by the TIDE and TIMAS instruments on the ISTP/POLAR spacecraft
Huddleston, Matthew Mark
Master of Science
Acceleration of ions transverse to the local magnetic field is ultimately necessary for gravitationally bound ionospheric plasma to escape out to the magnetosphere. Transversely accelerated ions (TAI's), which take the form of upflowing "conical" ion distributions, are not completely understood and are the subject of this thesis. TIDE and TIMAS are highly sensitive ion mass spectrometers carried by NASA's Polar spacecraft and capable of exceptional temporal, spatial, and energy resolution. Polar's elliptical orbit allows these instruments to sample auroral outflows at low altitudes near common source regions of transverse energization and also at high altitudes where conics are rarely reported. Four conic events observed by both TIDE and TIMAS are compared with several possible acceleration mechanisms. Low altitude conics are found to be the result of resonant wave-particle heating, while high altitude transverse distributions appear to arise from acceleration through small-scale electromagnetic structures.