Modeling of solar wind control of the ring current buildup: A case study of the magnetic storms in April 1997

The ring current buildup depending on the solar wind density and the time‐dependent convection field is examined by using a particle tracing scheme. To obtain the current density, energetic protons injected from the night side boundary at L=9 are traced under the dipolar magnetic field and the Kp dependent model of the Volland‐Stern type convection field. The source distribution function at the boundary is assumed to be isotropic Maxwellian with a temperature of 5 keV and a number density depending on the solar wind density. We derive the corrected Dst (Dst*) from the Biot‐Savart integral over the whole three‐dimensional distribution of the calculated current density. The results are compared with the observed Dst* in the three successive storms in April 1997; the major variation of the Dst* is mainly due to the convection electric field and the solar wind density as well.