ENERGY-DISSIPATION DURING A SMALL SUBSTORM

The relative importance of the two most likely modes of input energy d issipation during the substorm of 8 May 1986, with an onset at 12:14 U T (CDAW 9E event), is examined here. The combination of data from the interplanetary medium, the magneto-tail and the ground allowed us, fir st of all, to establish the sequence of phenomena which compose this s ubstorm. In order to calculate the magnetospheric energetics we have i mproved the Akasofu model, by adding two more terms for the total magn etospheric output energy. The first one represents the energy consumed for the substorm current wedge transformation, supplied by the asymme tric ring current. This was found to be 39% of the solar wind energy e ntering the magnetosphere from the start of the growth phase up to the end of the expansion phase. The second term represents the energy sto red in the tail or returned to the solar wind. Our results suggest tha t the substorm leaves the magnetosphere in a lower energy state, since , according to our calculations, 23% of the energy that entered the ma gnetosphere during the whole disturbance was returned back to the sola r wind. Finally, it is interesting to note that during the growth phas e the driven system grow considerably, consuming 36% of the solar wind energy which entered the magnetosphere during this early phase of the substorm.