Fung, S. F., R. F. Benson, J. L. Green, M. F. Smith, D. L. Carpenter,
W. Calvert, D. L. Gallagher, P. H. Reiff, B. W. Reinisch, and W. W. L.
Taylor, Probing the magnetopause by the radio sounding technique,
presented at the Magnetopause Workshop, the University of Alaska
Fairbanks, AK, September 20-23, 1993.

Probing the Magnetopause by the Radio Sounding Technique

S F Fung, R F Benson, J L Green, and M F Smith (NASA Goddard Space
Flight Center, Greenbelt, MD 20771; fung@nssdca.gsfc.nasa.gov)
D L Carpenter (Starlab, Stanford University, Stanford, CA 94305)
W Calvert (Dept. of Physics and Astronomy, University of Iowa, Iowa
City, IA 52240)
D L Gallagher (NASA Marshall Space Flight Center, Huntsville, Al
35812)
P H Reiff (Dept. of Space Physics and Astronomy, Rice University,
Houston, TX 77251)
B W Reinisch (University of Massachusetts Lowell, Lowell, MA 01854)
W W L Taylor (Nichols Research Corp, Arlington, VA 22209)

This paper investigates the use of radio sounding to observe the
magnetopause.  Radio sounding techniques, which had been well
developed for ionospheric studies, can be applied to probe the
structure and dynamics of the magnetopause by extending the lower
frequency limit of the sounder to 3 kHz.  Unlike in situ spacecraft
observations which provide only local measurements, remote radio
sounding measurements from outside the plasmasphere can be used to
monitor the location and reconstruct the global structure of the
magnetopause, thereby yielding much information on the dynamic
coupling between the solar wind and the magnetosphere.  Using ray
tracing, we will simulate the multi-frequency radio echoes returned
from the magnetopause to a spacecraft orbiting beyond the
plasmasphere.  Furthermore, it will be demonstrated that the time
delays of the radio echoes at different frequencies and arriving from
different directions can be used to determine the 3-dimensional plasma
structure, shape and instantaneous location of the magnetopause. 
These unique observations, if performed on polar orbiting spacecraft
such as the upcoming Inner Magnetospheric Imager (IMI), will allow the
magnetospheric response to the time varying solar wind conditions to
be determined.