Plasma mass density in the plasmatrough: Comparison using ULF waves and CRRES

Observations of ULF field line resonances detected by seven magnetometers i n the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) array were used to estimate equatorial cold plasma mass densities in and a round the plasmatrough region as a function of both radial distance and tim e of day. The magnetometers ranged in latitude from Pinawa (L=4.3) to Ranki n Inlet (L=12.4). The equatorial cold plasma mass densities were estimated using the T89 magnetic field model, an R-4 plasma density distribution func tion and the wave equation from cold plasma MHD theory. These ground based plasma mass density estimates were compared to those obtained from the CRRE S spacecraft. Typical values obtained from the ground based measurements we re similar to 2 H+ cm(-3) at L similar to 10 to similar to 10 H+ cm(-3) at L similar to 7. The data recorded on 3 October, 1990 showed excellent agree ment with the spacecraft observations for 8.5<L<10. It was found that the d ifferences between ground based estimates of plasma mass density and the va lues derived from spacecraft observations increased in regions of large pla sma mass density spatial gradients. This result may be explained in terms o f the spacing of magnetometers in the ground based array.