Changes in magnetospheric configuration during the substorm growth phase.

Investigation of various changes in the configuration of the geomagnetic tail that occur during the growth phase of magnetospheric substorms. A flaring-tail model indicates that the observed increases in geomagnetic tail field are explained if the dayside magnetopause shrinks by 1 to 2 earth radii. Increased tail flaring also requires that the tail current sheet approach near the earth during the growth phase. The motion of the inner edge of the plasma sheet, and consequently an equatorward shift of the nightside auroral oval, is consistent with the structural modifications mentioned above.