LONGER MAGNETIC STORMS. “In the same way, the strong ring current causes stretching of the magnetic field during magnetic storms, but in this case the changes occur over time scales of days rather than hours. Substorm activity during magnetic storms causes quasiperiodic stretching-dipolarization cycles embedded within the longer-term ring current-associated changes.”
https://link.springer.com/article/10.12942/lrsp-2007-1