VIOLENT OUTPUT. “Substorms typically occur at a rate of four to five per day, each lasting typically two to three hours. They are initiated by enhanced dayside reconnection and hence increased energy input to the magnetosphere. This causes a configuration change in the magnetosphere including enhancement of the magnetospheric current systems and formation of a thin and intense current sheet from near-geostationary distance outward.”
https://link.springer.com/article/10.12942/lrsp-2007-1