The storm-substorm relationship

Abstract:

The relation between geospace magnetic storms and magnetospheric substorms has been a long-standing and rather controversial research topic in magnetospheric physics. Storms and substorms are the most complex collective phenomena of energy dissipation resulting from enhanced solar wind – magnetosphere coupling. They share important common elements like magnetic field reconfigurations, particle acceleration and auroral displays, but also have big differences regarding their spatial and temporal extent, as well as their energy budget. Injection of ions into the night-side inner magnetosphere is a key feature of substorms, while the formation of an intense ring current around Earth is the defining key feature of storms. The Chapman-Akasofu paradigm of the ring current being the cumulative result of ion injections by consecutive substorms, has been disputed by other researchers supporting the view that the ring current is not a product of substorm injections, but of large-scale plasma convection from the magnetotail to the inner magnetosphere. Between the two extreme views, there is space for a substantial substorm contribution to ring current growth, through the preferential acceleration of ionospheric-origin oxygen ions, which dominate the ring current during intense storms. The substorm-driven oxygen ion component presumably also plays an important role in the two-step recovery of intense storms and in the growth of certain electromagnetic waves that influence storm-time radiation belt dynamics.