To gain a more comprehensive view of the powerful and dynamic plasma processes occurring during ionospheric storms, ground- and space-based observations using Global Navigation Satellite System (GNSS) signals have been analyzed. Several case and statistical studies of ionospheric storms are presented, clearly showing the generation and propagation of ionospheric disturbances. Discussed are the capabilities of advanced techniques for routine monitoring of the ionosphere and studying the ionospheric perturbations. It is concluded that the permanent monitoring of the ionosphere-plasmasphere system can play a significant role in mitigating adverse space weather effects on GNSS-based positioning.