Field line dependence of magnetospheric electron density

Observations of the electron density ne based on measurement of the upper hybrid resonance frequency by the Polar spacecraft Plasma Wave Instrument (PWI) are available for March, 1996 to September, 1997, during which time the Polar orbit sampled all MLT values three times. Using this data set, we assume a power law form for the electron density dependence along field lines ne = ne0 (Rmax/R)α, where ne0 is the equatorial electron density and Rmax ≈ LRE is the maximum geocentric radius R to any point on the field line, and model the statistical average of α as αmodel = 8.0 − 3.0 log10ne0 + 0.28 (log10ne0)2 − 0.43(Rmax/RE) for all categories of plasma (plasmasphere and plasmatrough), with an average error of 0.65. The data set on which this result is based is limited to 2.5RE ≤ Rmax ≤ 8.5RE, 2RE ≤ R ≤ Rmax, and 2 ≤ ne0 ≤ 1500 cm−3. There is no remaining dependence of the average α – αmodel on MLT or Kp.