Structure of the magnetospheric magnetic field during magnetic storms

We report the results of a study of the contributions of the large-scale ma gnetospheric currents to the observed Dst variation. Ground-based magnetome ter data during four magnetic storms (January 27-30, 1985; November 23-27, 1986; January 14-16, 1988; and May 6-8, 1988) were used to calculate Dst, a nd the paraboloid model of the magnetospheric magnetic held [Alexeev et al. , 1996] was used to determine the contribution of each magnetospheric curre nt system. Input data for our model were the solar wind plasma parameters, the interplanetary magnetic field (IMF) B-z, DMSP F6, F7, F8, and F9 satell ite observations of precipitating auroral particles, and Active Magnetosphe ric Particle Tracer Explorers (AMPTE)/CCE satellite measurements of the tot al energy of the ring current ions with energy per charge between 1.5 and 3 00 keVq(-1) We found good agreement between observed and modeled magnetic f ields during the main phase of the magnetic storms. Using the paraboloid mo del, we have determined the contributions to Dst of different magnetospheri c current systems including the magnetopause current B-CF, the symmetric ri ng current B-R, and the geotail current B-T Such separation shows that valu es of B-T and B-CF are comparable with the value of B-R during the main pha se of the storms. During the recovery phase the effect of B-R predominates.