**Abstract**

The transpolar convection of plasma and embedded magnetic fields generated by the solar wind interaction with the magnetosphere can be characterized by the polar cap (PC) indices, PCN (North) and PCS (South). These indices are derived from polar magnetic variations and calibrated with respect to the solar wind merging electric field (coupling function), *E*M, considered to control the entry of solar wind energy into the magnetosphere providing power to disturbance processes such as magnetic storms, auroral substorms, and upper atmosphere heating. Thus, the PC indices could be used to quantify the solar wind intensities for solar-terrestrial research and to survey the entry of solar wind energy for space weather monitoring. The closest relations between PC indices and the geomagnetic disturbance processes are obtained by using the dual polar cap PCC indices built from the positive values of PCN and PCS. The present work demonstrates that the transpolar convection processes characterized by the PCC indices are closely related to the intensities of auroral electrojet currents, to substorm occurrences, and to the building of magnetospheric ring currents in the equatorial region at 4–6 earth radii distance.

**Keywords:** solar wind/magnetosphere interactions, polar cap index, auroral electrojet currents, magnetospheric ring currents, magnetic storms and substorms, space weather forecasting.
