Relationship between ionospheric electric fields and magnetic activity indices

The relations between electric fields in the daytime and nighttime sectors of the polar ionosphere and magnetic activity indices of auroral region (AL) and northern polar cap (PCN) are studied. It is found that the above relations do exist and are described by: a) equations U _pc⁽¹⁾ (kV) = 27.62 + 21.43PCN with a correlation coefficient R = 0.87 and U _pc⁽¹⁾ (kV) = 4.06 + 49.21PCN - 6.24 PCN² between the difference in the electric potentials across the polar cap in the daytime sector U _pc⁽¹⁾ and PCN and b) regression equation U _pc⁽²⁾ (kV) = 23.33 + 0.08|AL| with R = 0.86 between the difference in the electric potentials across the polar cap in the nighttime sector U _pc⁽²⁾ and |AL|. It is shown that: a) it is possible to use the AL and PCN indices for real-time diagnostics of instantaneous values of the electric fields in the daytime and nighttime sectors of the polar ionosphere in the process of a substorm development; b) at the expansion phase of a substorm, due to calibration of PCN values by the values of the solar wind electric field E _sw, the PCN index does not feel the contribution of the western electrojet and, accordingly, the contribution of the nighttime ionospheric electric field U _pc⁽²⁾, governed by the reconnection in the magnetospheric tail.