Index of the PE magnetospheric gap and short-term forecasting of the explosive phase of a substorm

Suggested was a new geomagnetic index PE, summing-up the perturbation amplitudes of the field horizontal component at the stations of the magnetospheric fissure zone. Localized in the magnetospheric fissure zone is the polar electrojet, that forms the high-latitude effect of the azimuthal component of the interplanetary magnetic field. The PE-index also reflects the oscillations of the DP-2 system; this is proved by its correlation with the potential of the ''morning-evening'' electrical field. It is shown that the PE-index is applicable for the forecastina of the explosive substorm phase. The use of the PE-index to forecast the isolated substorms ensures the advent of approximately 80 and 90 % of the forecasted substorms with the 3 and 1-2 term, respectively