Formation of large-scale, "giant" undulations at the equatorial boundary of diffuse aurora and Pc5 magnetic pulsations during the January 14, 1999 magnetic storm

In the present study we investigate the undulations at the equatorial boundary of diffuse aurora and their relationship to the development of magnetic and auroral substorms and excitation of Pc5 magnetic pulsation on January 14, 1999. The observed undulations had wave-length of ~200-300 km and amplitude of ~50-250 km and they propagated westward with the velocity of ~0,7 km/s. It is found that the undulations began ~40 min after the substorm onset and lasted for ~80 min, all the way to the end of the substorm. During both active and recovery phases of the substorm the undulations were accompanied by the enhancement of the DP2 equivalent current system and by the formation of WTS. Concurrently with undulations, there were observed Pc5 magnetic pulsations of an oscillation period roughly equal to the ratio of the undulation wavelength to their propagation velocity. Observations are interpreted in terms of the shear/ballooning instability excitation near the plasmapause and subsequent generation of drift hydromagnetic waves.