HR: 17:15h
AN: SM54A-06    [Abstracts]
TI: The Ion Aurora and Its Seasonal Variations
AU: * Newell, P T
EM: Patrick.Newell@jhuapl.edu
AF: Johns Hopkins U. Appl. Phys. Lab., 11100 Johns Hopkins Rd., Laurel, MD 20723
AU: Wing, S
EM: Simon.Wing@jhuapl.edu
AF: Johns Hopkins U. Appl. Phys. Lab., 11100 Johns Hopkins Rd., Laurel, MD 20723
AU: Sotirelis, T
AF: Johns Hopkins U. Appl. Phys. Lab., 11100 Johns Hopkins Rd., Laurel, MD 20723
AU: Meng, C -
EM: Ching.Meng@jhuapl.edu
AF: Johns Hopkins U. Appl. Phys. Lab., 11100 Johns Hopkins Rd., Laurel, MD 20723
AB: Recent studies have shown that intense discrete aurora, auroral kilometric radiation, upflowing ion beams, and downward directed electric fields are more intense in the winter hemisphere than in the summer. This is particularly true of the dusk to midnight sector where intense electron aurora are most common. Here, we use one solar cycle of DMSP satellite particle data to investigate the seasonality of the ion aurora. The ion aurora proves to be approximately equal in the summer and winter hemispheres in the dusk-midnight sector (with the summer hemisphere favored by 0 to 4 percent). However in the MLT hours from midnight to dawn, the ion precipitating energy flux is 15-40 percent higher in winter than in summer. The absolute magnitude of the ion effect is smaller than was found for discrete electron aurora (which show a 3-fold difference between winter and summer). The seasonal behavior of the ions may reflect the observation that diverging electric fields, which accelerate ions downward, are found mainly postmidnight, and are stronger in the winter. The relative weakness of the seasonal effects in ions may reflect their high average energy (many tens of keV), which is substantially larger than typical of electric potentials found in the auroral circuit. Ions in the dusk to midnight sector are most intense equatorward of the region of discrete aurora, and are thus probably not much affected by the seasonality of the field-aligned electric fields which exist there (and which are of the sense to retard ion precipitation). Interestingly, ion average energies are higher in the winter hemisphere than in the summer hemisphere at all local times, regardless of whether or not energy fluxes are enhanced.
UR: http://sd-www.jhuapl.edu/Aurora
DE: 2451 Particle acceleration
DE: 2455 Particle precipitation
DE: 2704 Auroral phenomena (2407)
DE: 2716 Energetic particles, precipitating
DE: 2736 Magnetosphere/ionosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting