Plasma Density Distribution Along the Magnetospheric Field: RPI Observations From IMAGE
B.W. Reinisch 1, X. Huang 1, P. Song 1, G. S. Sales 1, S. F. Fung 2, J. L. Green 2, 
D. L. Gallagher 3, and V. M. Vasyliunas 4. 

1 Environmental, Earth, and Atmospheric Sciences Department, Center for Atmospheric Research, 
  University of Massachusetts Lowell
2 NASA Goddard Space Flight Center, Greenbelt, MD
3 NASA Marshall Space Flight Center, Huntsville, AL
4 Max-Planck-Institut fŸr Aeronomie, 37191 Katlenburg-Lindau, Germany

A new technique is introduced that remotely measures the plasma density profile in the 
plasmasphere. Radio plasma imager (RPI) echo observations provide echo delay time as function 
of frequency, from which the plasma density as function of position along the magnetic field 
line can be calculated.  An example from the nightside plasmasphere (L=3) shows the density 
having its minimum value near the equator and rapidly increasing densities along the field 
line above 40° magnetic latitude. The density increases at a faster rate toward the ionosphere 
than the field strength. The index of the power law of the density as a function of field 
strength increases from a few tenths near the equator to close to unity near 40° and greater 
than 2 near the ionosphere.

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Geophysical Research Letters, 28, 4521-4524, December, 2001