A high latitude electron density model derived from image/RPI sounding 

Nsumei, P., Huang, X., Reinisch, B.W., Song, P., Vasyliunas, V.M. 


The plasma density distribution over the polar cap is difficult to assess with 
insitu measurements because it is rare to have a few satellites along the same 
field line or geocentric direction. The existence of constant upward and 
downward flow of plasma, which may be directly or indirectly associated with 
geomagnetic activities, polar wind and/or polar rain also makes any 
theoretically derived polar density distribution based on the assumption of 
static plasma invalid. The Radio Plasma Imager (RPI) on board the IMAGE 
satellite uses a radio sounding technique for the remote sensing of plasma 
densities in the magnetosphere. In this study, the electron density is 
determined by inverting the R-X mode echo traces. With a new profile inversion 
routine, RPI data sets of IMAGE high-latitude passes over the period from May 
2000 to March, 2001, covering the polar region with invariant latitudes greater 
than 70 degrees, and measuring electron densities from ~1.4 to 5.0 RE were 
analyzed. Presented in this report are high latitude electron density profiles 
in solar magnetic coordinates and an empirical model of polar cap electron 
density distribution derived as a function of radial distance and geomagnetic 
activity. The derived empirical relation gives a better understanding of the 
variation of polar cap electron density with geocentric distance and the 
magnitude of the effect of geomagnetic activity on the polar cap electron 
densities. 
 
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Presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002