Chen, J.,
Co-Authors: and T. A. Fritz,
Title: Origins of Energetic Ions in CEP Events and Their Implications,
Reference: Int. J. Geomagnetism and Aeronomy, 2, 31-44, 2000.
Reference Type: Published Journal
CEPPAD: true
CAMMICE: true
RAPID: false
Abstract:
A new magnetospheric phenomenon called a cusp energetic particle (CEP) event has been discovered by the POLAR in 1996 [ Chen et al., 1997a, 1998]. The events were detected in the dayside cusp for hours at a time with an individual event lasting for tens of minutes. Each of these events were associated with a dramatic decrease and large fluctuations in the local magnetic field strength. The measured ions had energies up to 8 MeV. The enhancement of the energetic electron fluxes are much less than that of energetic ion fluxes. The charge state distribution of these ions was indicative of their source being recently the solar wind. Since the typical energy of the solar wind plasma is ~ 1 keV, a fundamental question is where do the cusp MeV ions come from? Simultaneous observations indicated that the ion fluxes in the CEP events were higher than that in both upstream and downstream from the bow shock. The turbulent power of the local magnetic field in the ultra-low frequency (ULF) ranges is correlated with the intensity of the MeV ions. Such ULF ranges correspond to periods of ~ 0.33-500 seconds that cover the gyro-, bounce-, and drift-periods of tens of keV to MeV charged particles when they are temporarily confined in the high-altitude dayside cusp. These observations represent a discovery that the high-altitude dayside cusp is a new acceleration and dynamic trapping region of the magnetosphere. Energetic ions were also measured in the vicinity of the cusp and the dayside quasi-trapping region with a time-energy-dispersion (TED) signature [ Karra and Fritz, 1999]. Both the TEDs and CEPs were found to have a peak in their frequency of occurrence around 14 hours local time. Trajectory calculations indicate that the cusp geometry is connected via gradient and curvature drift of these energized ions to the equatorial plasma sheet. This implies that the dayside cusp is potentially an important source of magnetospheric particles.
