Accuracy of the RPI plasmaspheric electron density profiles

Xueqin Huang (1), Bodo W. Reinisch (1), Gary Sales (1), and James L. Green (2)

1 - University of Massachusetts Lowell Center for Atmospheric Research
    600 Suffolk Street, Lowell MA 01854
2 - Goddard Space Flight Center, NASA


Profile inversion techniques have been developed to derive electron density
profiles in the plasmasphere [Reinisch et al., GRL, 28, 1167, 2001] and the
polar cap [Nsumei et al., JGR, in press, 2003] from echo traces on the
plasmagrams recorded by the radio plasma imager (RPI) on the IMAGE
satellite. Our analysis of the long-range discrete echo traces indicates
propagation of the electromagnetic waves along the magnetic field line
through the satellite location. This field-aligned propagation for
frequencies above the electron plasma frequency could be caused by
refraction and/or ducting due to field-aligned irregularities. To
investigate which of these mechanisms dominates the guiding process, we are
using ray-tracing techniques and simple duct shapes with adjustable
parameters. The simulations are then compared with the discrete X-mode echo
traces observed on the RPI plasmagrams, and the absence of O-mode echoes. If
the refraction in a medium of changing electron density and magnetic field
strength is the dominant guiding factor, the wave will be reflected at the
location where the wave frequency equals the cutoff frequency of the
magneto-plasma. If ducting is responsible for the field-aligned propagation,
reflection will occur slightly before this location, depending on the
percentage density enhancement of the duct walls. Results of these
simulations and reference to the observed echoes will provide answers
regarding the accuracy of the RPI electron density profiles, explain the
observed field guidance, and, if applicable, determine the duct shape
parameters. 

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URSI Meeting, Ohio State University, Columbus, Ohio, June 22-27, 2003