Computer Science – Sound
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm32a26b&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM32A-26
Computer Science
Sound
2487 Wave Propagation (6934), 2730 Magnetosphere--Inner, 2768 Plasmasphere, 2776 Polar Cap Phenomena
Scientific paper
The radio plasma imager (RPI) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite detects well-defined long-range echoes in the vicinity of the plasmapause. These echoes correspond to virtual ranges (i.e., assuming free-space speed-of-light velocities) often greater than an earth radius (RE) when the distance to the plasmapause is only of the order of 0.1 RE. The virtual ranges are consistent with distances to the polar-cap ionosphere. The location of IMAGE relative to the polar-cap ionosphere suggests that the RPI echoes may result from waves that are guided (or ducted) along electron-density irregularities that are maintained along the direction of the background magnetic field. Such field-aligned propagation is common in the topside ionosphere and can result in an increase in the echo signal by 20 to 40 dB [G. E. K. Lockwood, J. Geophys. Res., 78, pp. 2244-2250, 1973] over that expected from inverse-square path loss. We investigate the received signal strengths of the RPI echoes in order to identify which ones can be attributed to wave ducting. We first demonstrate the technique by using ISIS 1 ionospheric topside-sounder ionograms recorded near apogee (3500 km) at low latitudes in order to obtain the longest possible propagation paths across the direction of the terrestrial magnetic field. This geometry represents a difficult sounding condition because there is no field-aligned propagation to the ionospheric target below. Earlier investigations of echo signal strength were based on much shorter distances using either Alouette 1 at 1,000 km [L. E. Petrie et al., J. Geophys. Res., 70, pp. 4347 -4356 1965] or Alouette 2 at about 1,500 km [C. A. Franklin and M. A. Maclean, Proc. IEEE, 57, pp. 897-929, 1969]. The results of the investigation of the signal strengths of the RPI echoes obtained when IMAGE is in the vicinity of the plasmapause will be compared to the Alouette/ISIS ionospheric topside-sounder results and to the types of echoes expected for a magnetospheric radio sounder near the plasmapause.
Benson Robert F.
Carpenter Donald L.
Fung Shing F.
Galkin Ivan
Green James L.
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