Changes in magnetospheric configuration during the substorm growth phase

Four simple calculations suggest that the magnetosphere changes its configuration during substorm growth phase. A flaring tail model indicates that the observed increases in geomagnetic tail field can only be explained if the dayside magnetopause shrinks by 1-2 RE. The same assumption is needed to explain large magentic decreases observed at geostationary orbit. A plasma sheet model, consistent with a flaring tail, indicates that increased tail falring leads to plasma sheet thinning, and a decrease in northward magentic field, during substorm 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 above structural modifications. (Author)