Relationship between the Dst variation and the geometry of the magnetosphere

The geomagnetic field produced by currents at the magnetopause and in the plasma sheet is calculated assuming that the plasma pressure in the plasma sheet significantly exceeds the magnetic pressure. It is shown that the geomagnetic disturbance in this case depends only on two parameters: (1) the solar-wind pressure and (2) the area of the high-latitude ionospheric region projected into the plasma sheet and the magnetotail. The calculation results agree well with the observed dependence of the Dst variations on the latitude of the equatorial boundary of the auroral zone.