Model of changing magnetosphere
As it travels towards Earth's orbit, the solar wind transports magnetic field lines from the Sun, known as the interplanetary magnetic field (IMF). This IMF can be very dynamic, due to the strong gusts often exhibited by the solar wind, and to the fluctuations both in magnitude and orientation of the IMF. As a result, dramatic dynamical changes can occur in the entire magnetospheric configuration, which culminate in magnetospheric storms, accompanied by an explosive conversion of large amounts of the solar wind energy into the kinetic energy of charged particles in the near-Earth space. This latter activity is manifested in polar auroral phenomena and ionospheric disturbances.
This animation illustrates the dynamical changes of the global magnetic field in the course of a disturbance: a temporary compression of the magnetosphere by enhanced flow of the solar wind is followed by a tailward stretching of the field lines. Eventually, the increase of the tail magnetic field results in a sudden collapse of the nightside field (a substorm) and a gradual recovery of the magnetosphere to its pre-storm configuration. (Further details can be found here.)