ULF Waves Associated with Enhanced Subauroral Proton Precipitation

T. J. Immel, (UC Berkeley, Berkeley, CA 94720) S. B. Mende, J. W. Bonnell,
H. U. Frey, M. Thomsen

Several types of sub-auroral proton precipitation events have been
identified using the Spectrographic Imager (SI) onboard the NASA-IMAGE
satellite, including dayside subauroral proton flashes and detached proton
arcs in the dusk sector. These have been observed at various levels of
geomagnetic activity and solar wind conditions, but the mechanism driving
the precipitation has often been assumed to be scattering of protons into
the loss cone by enhancement of ion-cyclotron waves in the interaction of
the thermal plasmaspheric populations and more energetic ring current
particles. Indeed, recent investigation of the detached arcs using the MPA
instruments aboard the LANL geosynchronous satellites has shown there are
always heightened densities of cold plasma on high-altitude field lines
which map down directly to the subauroral precipitation signature. If the
ion-cyclotron instability is a causative mechanism, the enhancement of wave
activity at ion-cyclotron frequencies should be measurable. In this
presentation, a review of the observations to date, and a survey of data
from the ground- and space-based instruments which may provide a
confirmation of the enhanced wave activity will be shown. Discussion of
other possible mechanisms for the precipitation will follow.

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions, 
3 - 6 February 2004, Yosemite, California, USA