Ray-Tracing Modeling of Guided Echoes Detected by Radio Plasma Imager on the
IMAGE Satellite

Shing F. Fung (1), Venku Jayanti (2), James L. Green (1), William W. Taylor (2)

1 - NASA GSFC, Greenbelt, MD
2 - Raytheon ITSS / NASA GSFC, Greenbelt, MD


Using the Radio Plasma Imager (RPI) aboard the Imager for Magnetopause-to-Aurora
Global Exploration (IMAGE) satellite, radio echo signatures with discrete
virtual range-frequency characteristics have been observed at different
altitudes and magnetic latitudes varying from the polar cap to the equator.
Long-range discrete echoes have also been observed to return from conjugate
hemispheres. Such observations, being analogous to very similar past
observations made in the ionosphere (at much lower altitudes), strongly suggest
that the radio signals have been ducted by field-aligned irregularities, similar
to the mechanism generally invoked to explain the ionospheric observations.
Reinisch et al [2001] recently suggested another possible signal guiding
mechanism due to the presence of field-aligned density gradients, such as might
be present over the polar cap regions. In this scenario, field-aligned
propagating radio signals can naturally follow the magnetic field line without
the trapping action of a density duct. In order to determine the mechanism
responsible for guiding of long-range discrete echoes observed in magnetospheric
plasmas by the RPI, we have performed ray-tracing modeling of discrete echo
propagation to investigate the plasma conditions needed to support ducting and
wave-guiding by a field-aligned density gradient. This paper discusses the
plasma models used and presents modeling results.


Reinisch, B. W., et al., Plasma Density Distribution Along the Magnetospheric
Field: RPI Observations From IMAGE, Geophys. Res. Lett., 28, 4521-4524, 2001.

_______________
Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002