ISO/TR 23989:2020 provides guidelines for specifying the qualitative estimation of the solar wind energy input into the magnetosphere with use of operative ground-based information on the polar cap magnetic activity (PC index).

The solar wind energy incoming into the magnetosphere predetermines development of the magnetospheric disturbances: magnetic storms and substorms. Magnetospheric disturbances include a wide range of phenomena and processes directly affecting human activity, such as satellite damage, radiation hazards for astronauts and airline passengers, telecommunication problems, outrages of power and electronic systems, effects in the atmospheric processes, and impact on human health.

This document is intended for on-line monitoring the magnetosphere state and nowcasting the intensity and extent of magnetic disturbances as well as parameters of the high-latitude ionosphere. The method and accuracy of estimating is ascertained by close relationship between the PC index and interplanetary electric field (as the most geoeffective solar wind parameter), on the one hand, and between the PC index and magnetoshpheric disturbances, on the other hand.