In Troshichev et al. (2006) an error was made in the calculations of Polar Cap (PC) index scaling parameters. For the publication commented here, Troshichev et al. (2011), the authors state having used scaling parameters of the invalid PC index version but have actually substituted parameters from another version instead. The mingling of PC index versions has resulted in erroneous illustrations in Figs. 1, 2, 3, 6, 7, and 8 and the issuing of non-substantiated statements.

The Polar Cap (PC) indices, PCN (North) based on magnetic data from Qaanaaq (Thule) and PCS (South) based on Vostok data, reflect the transpolar convection of plasma and magnetic fields. The PC indices could be used, among others, to indicate the energy transfer from the solar wind to the magnetosphere–ionosphere–thermosphere system in space weather monitoring applications. The present IAGA-endorsed methods to derive PC indices in real time are found to generate inconsistent index values.