Magnetospheric contribution to K-indices

The contributions of disturbances to solar regular (SR) curves (expressing the regular part of the variation of a magnetic element ascribed to ionospheric currents) and hence to the K-indices, are shown. To find examples where the K-values might have magnetospheric contributions, hand-scaled K-values or K-values produced with a computer method designed to imitate the hand scaling are compared. It is found to be impossible to derive the effects of solar wind and IMF from the records of one observatory only. The original requirements in the hand scaling of K-indices, which state that the night level of SR has to be smooth and flat, are not always valid physically. Existing high-latitude ionospheric current systems and corresponding field-aligned currents, which connect the high latitude ionosphere with the magnetospheric tail, influence the SR curves at middle latitudes.