Comment on “Unified PCN and PCS indices: Method of calculation, physical sense, and dependence on the IMF azimuthal and northward components” by O. Troshichev, A. Janzhura, and P. Stauning

摘要

Troshichev et al. [2006, hereinafter referred to as T06] presented newly calculated unified PC indices from both hemispheres that are ‘‘well consistent one with another in their value and behavior and linearly correlate with the solar wind merging electric field (MEF)’’ (p.1 of T06). Significant differences in the magnitude between the northern (PCN) and southern (PCS) indices produced by the Danish Meteorological Institute (DMI) and the Arctic and Antarctic Research Institute (AARI), respectively, was revealed after transition to the 1-min values [Lukianova et al., 2002]. Since the technique traditionally applied for calculation of the PCN and PCS is different to some degree, elaboration of the consensus between two institutions, the producers of the indices, is quite appreciated. However, careful examination of the changes introduced by T06 to the procedure and the results of these changes reveals some contradictions. T06 alleged that the newly applied smoothing of the coefficients and the choice of quiet d ly variation (QD) as the level of reference for magnetic disturbances have eliminated the systematic exceeding of the PCS over the PCN. The similarity of two indices was achieved in such a manner that the PCS became smaller while the PCN became larger.