Loading-unloading processes in the nightside ionosphere

The loading-unloading processes during magnetospheric substorms are examine d using the 'IL index' from the IMAGE magnetometer chain together with sola r wind and IMF data from the WIND spacecraft. The IL index is a local, midn ight sector, AL index. Energy input throughout the substorm is evaluated by integrating the epsilon parameter from the start of the growth phase until the end of the substorm. Energy dissipated in the ionosphere is estimated by integrating the IL index from the substorm onset to the end of the subst orm. We show that the best correlation with the energy dissipated in the io nosphere is given by the energy input to the system after the substorm onse t. Hence, we con elude that the energy loaded during the growth phase is ne cessary for the magnetospheric reconfiguration before the substorm onset, b ut that the size of the substorm as measured by the IL index is mostly gove rned by the direct energy input during the expansion phase.