Field-Aligned Plasma Density Profiles Derived from RPI Plasma Sounding

Paul Song, Xueqin Huang, Bodo Reinisch, Gary Sales, Grigori Khmyrov
Environmental, Earth, and Atmospheric Sciences Department 
Center for Atmospheric Research, University of Massachusetts Lowell

James Green and Shing Fung 
NASA Goddard Space Flight Center

The radio sounding conducted by the radio plasma imager (RPI) on board the
IMAGE satellite has produced some unexpected results. There are often two
types of echo traces: more diffusive and more discrete. The diffusive
traces appear to be formed by echoes radially reflected from plasma density
structures.  The sources and processes that produce the discrete traces
(often there are several of them in each experiment) have been puzzling.
The echoes appear to arrive at the satellite parallel or antiparallel to
the local magnetic field. Extensive tests of different modes and
propagation angles have shown that these traces can be formed by waves
propagating along the geomagnetic field from the satellite toward the
ionosphere and then being reflected back. The multiple traces are produced
by waves of different modes and propagation to different hemispheres. With
a given magnetic field model, the plasma density along the magnetic field
can be derived. We are in the process to develop an empirical model of the
plasma density distribution within 5 Re from the earth, i.e., the region
where the discrete echo traces occur most frequently.

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To be presented at the 10th International Ionospheric Effects Symposium
Alexandria, Virginia, USA, May 7-9, 2002.