Quasi-periodic ionospheric disturbances with a 40-min period during prolonged northward interplanetary magnetic field

It has been observed that quasi-periodic oscillations in the solar wind and interplanetary magnetic field (IMF) can result in the generation of aurora l electrojet bursts and gravity waves with a similar period. In this paper, we present radar and magnetometer observations of quasi-periodic ionospher ic disturbances during stable, northward IMF. Magnetic deviations of simila r to 10 nT with a 40-min periodicity were registered with ground magnetomet ers between magnetic latitudes 75 degrees and 80 degrees over an extended r egion along the longitudinal direction in the morning sector. A sequence of gravity waves were observed by HF radars at lower latitudes and appeared t o be closely related to the high-latitude 40-min current disturbances. Ther e were no obvious source perturbations in the upstream solar wind for the i onospheric disturbances. We suggest that field line resonances could be exc ited in a closed magnetosphere during prolonged northward IMF and result in the generation of the ionospheric current disturbances and gravity waves.