HR: 11:20h
AN: SM51E-05    [PDF]
TI: Examining Relativistic Electron Loss in the Outer Radiation Belt
AU: * Green, J C
EM: Janet.Green@noaa.gov
AF: National Oceanic and Atmospheric Administration Space Environment Center, 325 Broadway Blvd, Boulder, CO 80305 United States
AU: Onsager, T G
EM: Terry.Onsager@noaa.gov
AF: National Oceanic and Atmospheric Administration Space Environment Center, 325 Broadway Blvd, Boulder, CO 80305 United States
AU: O'Brien, P
EM: Paul.OBrien@aero.org
AF: Aerospace Corporation, PO Box 92957, Los Angeles, CA 90009-2957 United States
AB: Since the discovery of earth's radiation belts researchers have sought to identify the mechanisms that dictate the seemingly erratic relativistic electron flux levels in the outer belt. Contrary to intuition, relativistic electron flux levels do not always increase during geomagnetic storms even though these storms signify enhanced energy input from the solar wind to the magnetosphere [{\it Reeves et al}., 2003; {\it O'Brien et al.}, 2001]. The fickle response of the radiation belt electrons to geomagnetic activity suggests that flux levels are determined by the outcome of a continuous competition between acceleration and loss. Some progress has been made developing and testing acceleration mechanisms but little is known about how relativistic electrons are lost. We examine relativistic electron losses in the outer belt focusing our attention on flux decrease events of the type first described by {\it Onsager et al.} [2002]. The study showed a sudden decrease of geosynchronous $>$2MeV electron flux occurring simultaneously with local stretching of the magnetic field. The decrease was first observed near 15:00 MLT and progressed to all local times after a period of $\sim$10 hours. Expanding on the work of {\it Onsager et al. }[2002], we have identified $\sim$ 51 such flux decrease events in the GOES and LANL data and present the results of a superposed epoch analysis of solar wind data, geomagnetic activity indicators, and locally measured magnetic field and plasma data. The analysis shows that flux decreases occur after 1-2 days of quiet condition. They begin when either the solar wind dynamic pressure increases or Bz turns southward pushing hot dense plasma earthward to form a partial ring current and stretched magnetic field at dusk. Adiabatic electron motion in response to the stretched magnetic field may explain the initial flux reduction; however, often the flux does not recover with the magnetic field recovery, indicating that true loss from the magnetosphere is occurring. Using Polar and SAMPEX data, we examine whether precipitation to the atmosphere or magnetopause encounters can account for the additional loss.
DE: 2716 Energetic particles, precipitating
DE: 2720 Energetic particles, trapped
DE: 2731 Magnetosphere--outer
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting