Wave effects of sudden impulse and substorm onset in the magnetospheric morning sector on January 4, 2001

A comparative analysis of extremely low frequency waves registered by Cluster satellites after a sudden impulse (SI) and the following substorm onset (SO) at distances L ∼ 4 from the Earth’s center was performed. It was shown that both phenomena in the equatorial morning magnetosphere activated magnetic field oscillations of periods from 40 to 200 s. Oscillations accompanying SI and SO were found to be of similar spectral composition but different polarizations. The differences in polarization became well-pronounced near the main spectral maximum (100–130 s), where the transition from SI to SO was accompanied by reverse of rotation of the magnetic field disturbance vector and by reorientation of the oscillation polarization ellipse.