Storms and substorms—The new whole system approach and future challenges

Abstract This chapter covers our current understanding and recent advances in the study of Earth's ionosphere during magnetic storms and substorms with a special focus on electrodynamics and its consequences in the past 14 years. In particular, the focus is on the new awareness of looking at the magnetosphere, ionosphere, and thermosphere (M-I-T) as a whole system that has brought us to the next level of understanding. Both ground-based observations and the new space-based observations from magnetospheric missions are expanding rapidly. More and more compelling science questions cannot be addressed and resolved without combining simultaneous multiple observations in the ionosphere, plasmasphere, and magnetosphere in order to establish a consistent understanding of the system. Models have greatly improved mostly by coupling different regions and different species. New models can reproduce system phenomena that involve M-I-T coupling and help us elucidate the underlying processes within the coupled systems. Our future challenges will involve (1) cross-scale system and scale interactions; (2) the whole geospace modeling concept, including lower atmospheric forcing; (3) multiday forecasting capability.