HR: 0830h
AN: ED41B-1165    [PDF]
TI: Analysis of Compressional Pc 5 Magnetic Field Oscillations and Associated Energetic Ion Modulations Occurring on December 20, 2002 in the Dusk Sector Outer Magnetosphere
AU: * Greene, H L
EM: greeneh@augsburg.edu
AF: Augsburg College, 2211 Riverside Ave., Minneapolis, MN 55454 United States
AU: Engebretson, M J
AF: Augsburg College, 2211 Riverside Ave., Minneapolis, MN 55454 United States
AU: Erickson, K N
AF: Augsburg College, 2211 Riverside Ave., Minneapolis, MN 55454 United States
AU: Peterson, W K
AF: LASP, University of Colorado, Boulder, CO 80303 United States
AU: Trattner, K J
AF: Lockheed Martin Advanced Technology Center, 3251 Hanover St., Palo Alto, CA 94304 United States
AU: Cheng, C Z
AF: Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 United States
AU: Russell, C T
AF: IGPP, UCLA, Los Angeles, CA 90095 United States
AB: An intense compressional Pc 5 wave event was observed by Polar during a minor magnetic storm on 20-Dec-2002 as it crossed the geomagnetic equator near dusk (17:30 MLT) at L $\sim$ 9.6. The local magnetic field varied by a factor of two while fluxes of $\sim$10 keV energetic protons varied in anti-phase by a factor of three. The Dst index revealed a sudden commencement beginning at 08:00 UT on Dec. 19, and decreased to a minimum of -56 at 19:00 UT. Waves were observed from 01:00 to 03:00 UT on Dec. 20 as the Dst index showed an initial recovery from the storm. The region of proton flux and magnetic field oscillations was sharply bounded in magnetic latitude from -0.6$\deg$ to 4.1$\deg$. Proton fluxes with energy per charge from 1.0 to 21.5 keV/e showed a sharp anti-correlation with the total magnetic field, while proton fluxes with higher and lower energy were much weaker and showed little variation. Protons with pitch angles between 30$\deg$ and 150$\deg$ were essentially isotropic in azimuth and varied in anti-phase with the total magnetic field, while the much smaller fluxes with pitch angles below 30$\deg$ and above 150$\deg$ showed fluctuations with less obvious correlations to the magnetic field. The observed predominantly compressional wave can be attributed to a ballooning-mirror instability of observed energetic protons, excited when ion pressure gradients and pressure anisotropy are large, and are hence closely associated with magnetic storms. The localization of the waves near the geomagnetic equator in the outer dusk magnetosphere is consistent with such source mechanisms.
DE: 2720 Energetic particles, trapped
DE: 2752 MHD waves and instabilities
SC: Education and Human Resources [ED]
MN: 2003 Fall Meeting