Electron Density Distribution Over the Northern Polar Cap Deduced From
IMAGE/RPI Sounding

Nsumei, P,  Huang, X,  Reinisch, B,  Song, P,  Henize, V K

The plasma density distribution along the open field lines over the
polar cap is difficult to assess with in-situ measurements because it is
rare to have a few satellites along the same field line. It is also
challenging to derive it from theory because the existence of constant
upward or downward flow makes a static approximation invalid. The radio
plasma imager (RPI) echo soundings together with the new profile
inversion routines provide a direct method of obtaining this
distribution. We have analyzed IMAGE polar cap passes from June to
September 2000 measuring a 10-minute sequence of electron density
profiles up to ~5RE. We present the densities in the SM coordinate
system for magnetic co-latitudes <30 degrees. The possible
dependence of these distributions on the solar wind conditions and their
relation with the Kp index will be discussed.