Simultaneous satellite and ground-based observations of a discretely driven field line resonance

An analysis is presented of a set of toroidal field line resonances observed on the ground by CANOPUS magnetometers and scanning auroral photometers on December 13, 1990, following a substorm onset at 0750 UT and intensification at 0850 UT. Magnetic and electric field data from the CRRES satellite provide evidence that the resonance was also observed in the magnetosphere. To our knowledge, this is the first report of discretely driven resonances observed by ground-based magnetometers and photometers and confirmed using satellite data. A spectral peak at 2.1 mHz is present in all data sets at approximately the same invariant latitude and universal time, indicating that CANOPUS and CRRES are observing the same resonance. Peaks are also present at 1.4 and 1.7 mHz in the ground-based magnetometer and CRRES data at a slightly higher latitude with corresponding spectral peaks apparent in the photometer data. The ground signature for each resonance indicates an antisunward phase velocity, suggesting that the excitation source is in the vicinity of the dayside magnetosphere, consistent with a waveguide model of the magnetosphere but not with a cavity model. This fact, combined with a possibly enhanced solar wind dynamic pressure, suggests that the substorm was not directly responsible for exciting the resonances. The interaction of the resonances with the substorm remains unclear except for the luminosity fluctuations associated with the resonances.