Abstract
Abstract. The only published description of the solar wind sector (SS) term used for the reference level in the post-event and real-time derivation of the Polar Cap (PC) indices, PCN (Polar Cap North) and PCS (Polar Cap South), in the version endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) is found in the commented publication, Janzhura and Troshichev: Identification of the IMF sector structure in near-real time by ground magnetic data, Annales Geophysicae, 29, 1491–1500, 2011. Actually, the publication has served as a basis for the index endorsement by IAGA in 2013. However, neither the illustrations nor the results presented there have been derived by the specified near real-time method. Figures 1, 6, 7, and 8 display values derived by post-event calculations based on daily medians smoothed over 7 d centred on the day of interest. Figures 2, 3, and 4 display observed values smoothed over 7 d, while the remaining Fig. 5 displays averages over 4 months. In summary, there are strong disagreements between indications in the title, abstract, and statements in the text compared to the actual results and their illustrations.
Highlights
The derivation of the Polar Cap (PC) indices, PCN (Polar Cap North) based on Qaanaaq data and PCS (Polar Cap South) based on Vostok data, in the versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) in Resolution no. 3 (2013) is to a large extent based on the methods described in Janzhura and Troshichev (2011): Identification of the interplanetary magnetic field (IMF) sector structure in near-real time by ground magnetic data
This work provides the only published description of the solar wind sector (SS) term related to the Y component, IMF BY, of the interplanetary magnetic field (IMF)
The SS terms are derived from daily median values of the recorded magnetic field components and added to the index reference level in the post-event or near real-time versions
Summary
The derivation of the Polar Cap (PC) indices, PCN (Polar Cap North) based on Qaanaaq data and PCS (Polar Cap South) based on Vostok data, in the versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) in Resolution no. 3 (2013) is to a large extent based on the methods described in Janzhura and Troshichev (2011): Identification of the IMF sector structure in near-real time by ground magnetic data (hereinafter J&T2011) The SS terms are derived from daily median values of the recorded magnetic field components and added to the index reference level in the post-event or near real-time versions. For post-event PC index calculations, the SS terms are derived from 7 d averaging of daily median values of the recorded magnetic data. For the near real-time calculations, the SS terms are derived from cubic spline-based forward extrapolation of past median values. The method is invalid since it assumes that the IMF BY -related effects originating at the dayside cusp region can be compensated for by using a daily median-based SS term at all local hours. The solar wind sector “compensation”, typically, generates unfounded contributions to the PC indices at the nightside the real IMF BY effects on polar magnetic fields at the night side are usually very small.
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