The Variation of Plasmatrough Density Derived from Magnetospheric Field Line Resonances

C.L. Waters 1, J.C. Samson 2 and E.F. Donovan 3

Physics Department, University of Newcastle, New South Wales, Australia 1
Physics Department, University of Alberta, Alberta, Canada 2
Physics Department, University of Calgary, Alberta, Canada 3


The diurnal variation of ULF field line resonant frequencies has been calculated using the cross phase of data from the north-south components recorded at 7 latitudinally spaced ground magnetometers in the CANOPUS array. CANOPUS magnetometers range in latitude from Rankin Inlet (L=12.4) south to Pinawa (L=4.3). Using cold plasma MHD theory, an R-4 plasma density function and the T87 magnetic field model, the variation of plasma density in the equatorial region has been calculated from the experimentally determined resonant frequencies. Consecutive, adjacent magnetometer pairs provide 6 local daytime spatial estimates of the variation in plasma density between 4 and 11 RE. Typical values of plasma number densities are 1-20 cm-3 for the plasmatrough and 50-200 cm-3 for the plasmasphere. The data recorded on June 7, 1990 shows an afternoon increase in plasma density near geosynchronous orbit in agreement with convection models of the magnetosphere. The ground based measurements of plasma density have been compared with data from the CRRES and Los Alamos Magnetospheric Plasma Analyser (MPA) on board the 1989-046 geosynchronous spacecraft. These comparisons show that the ground based technique should allow a robust procedure for calculating dayside, time-dependent mappings of the equatorial plasma density from the plasmapause to the magnetopause in near real time.

Plasma Density Profile Plasma Density Profile