Comparison of the modelled region of open field lines with the observed poleward boundary of auroral electron precipitation.

The geometry of the open field line regions in the earth's magnetosphere is calculated by utilizing the Olson-Pfitzer 1974 geomagnetic field model upon which a uniform interplanetary magnetic vector field is superimposed. Results of these calculations are compared to observations of the poleward boundary of the auroral electron precipitation region on a case-by-case basis as made by the Defense Meteorological Satellite Program (DMSP)- F2 satellite. This boundary is considered to be a very good indicator of the transition from open to closed field lines. The satellite data used were taken during geomagnetically quiet intervals: for this set, the median predicted latitude is found to be 1.7degrees equatorward of the median observed latitude.