The publication by Stauning (2022b, 10.1029/2022JA030355 ): “The use of invalid Polar Cap South (PCS) indices in publications.” Journal of Geophysical Research: Space Physics , 127 , e2022JA030355 is based on values of the PCS indices derived at the Arctic and Antarctic Research Institute (AARI) by the authors of the Comment and made available at the web portal maintained by the International Service of Geomagnetic Indices (ISGI) supported by the International Association for Geomagnetism and Aeronomy and also at the web portal maintained by AARI. One PCS version (“pre‐2021PCS”) comprises a series of indices spanning 1997–2021 published by AARI up to December 2021 and by ISGI up to April 2022. Since no other PCS version has been in play at AARI prior to 2021, this version, labeled “provisional” by ISGI, was beyond doubt used in the 9 publications listed in the commented publication by Stauning (2022b, 10.1029/2022JA030355 ). A modified PCS version (“post‐2021PCS”) was published by AARI in December 2021 and recently by ISGI (May 2022). The pre‐2021PCS version has been proven invalid by many examples of unfounded excessive index excursions and also by comparisons with indices of the post‐2021PCS index version. Its devaluating imprints on the publications issued by AARI between 2014 and 2021 are indisputable regardless of later modifications of the PCS index series.

Examination of the contribution from O.A. Troshichev, S. Dolgacheva, N.A. Stepanov, and D.A. Sormakov: “The PC index variations during 23/24 solar cycles: relation to solar wind parameters and magnetic disturbances. https://doi.org/10.1029/2020JA028491 ” has disclosed inconsistencies in the applied methods and serious errors in the calculated values. Some of the discrepancies reported in the present commentary affect directly the illustrations presented in their contribution while other possible errors may not be apparent since the use of relative values in their presentation makes thorough assessments difficult.

The standard polar cap (PC) indices, PCN (North) based on magnetic data from Qaanaaq in Greenland and PCS (South) based on data from Vostok in Antarctica, have been submitted from the Arctic and Antarctic Research Institute in St. Petersburg, Russia, the Danish Meteorological Institute, and the Danish Space Research Institute in different versions. In order to consolidate PCS indices based on Vostok data or replace poor or missing index data, derivation procedures have been developed to generate alternative PCS index values based on data from Dome Concordia (Dome‐C) magnetic observations from epoch 2009–2020 of solar cycle 24. The reference levels and calibration parameters needed for calculations of Dome‐C‐based PCS values in post‐event and real‐time versions are defined and explained in the present work. Assessments of the new PCS index have shown its unprecedented high relevance. Part of the methods used here, such as the quiet reference level construction and the correlation and regression procedures used for calculations of scaling parameters, deviate from corresponding features considered inadequate of the International Association for Geomagnetism and Aeronomy‐endorsed PC index derivation methods.

The transpolar convection of plasma and embedded magnetic fields generated by the solar wind interaction with the magnetosphere can be characterized by the polar cap (PC) indices, PCN (North) and PCS (South). These indices are derived from polar magnetic variations and calibrated with respect to the solar wind merging electric field (coupling function), EM, considered to control the entry of solar wind energy into the magnetosphere providing power to disturbance processes such as magnetic storms, auroral substorms, and upper atmosphere heating. Thus, the PC indices could be used to quantify the solar wind intensities for solar-terrestrial research and to survey the entry of solar wind energy for space weather monitoring. The closest relations between PC indices and the geomagnetic disturbance processes are obtained by using the dual polar cap PCC indices built from the positive values of PCN and PCS. The present work demonstrates that the transpolar convection processes characterized by the PCC indices are closely related to the intensities of auroral electrojet currents, to substorm occurrences, and to the building of magnetospheric ring currents in the equatorial region at 4–6 earth radii distance.

Polar Cap (PC) indices, PCN North based on magnetic observations from Qaanaaq (THL) in Greenland and PCS South based on magnetic data from Vostok in Antarctica, are very useful indices for studies of solar wind‐magnetosphere interactions and for space weather monitoring and forecasts. PCN indices are issued from the Danish Space Research Institute (DTU Space) while PCS indices are issued from the Arctic and Antarctic Research Institute (AARI) in St Petersburg. Unfortunately, series of invalid PCS values have been provided from AARI and used in a number of publications issued since the PC index concept was endorsed by the International Association of Geomagnetism and Aeronomy (IAGA) in 2013. In spite of the disclosure of the failure in the PCS indices in 2018, publishing at the IAGA‐supported International Service of Geomagnetic Indices of the invalid indices has continued up to now (2022). The present contribution defines the invalidating features of the PCS indices in question, conveys examples, and discusses the applications in peer‐reviewed publications.

Abstract The present study confirms the validity of previously derived relations between the polar cap (PC) indices and the ASY‐H and the Dst and SYM‐H ring current indices when used in real‐time applications. PC indices are here derived in simulated real‐time (SRT) versions by using past data only from −40 days up to current time in the construction of the quiet reference levels (QDCs) for the magnetic data. From analyses spanning a decade (2009–2018), equivalent ASY‐H index values were derived from a linear relation with SRT PCN (North) and PCS (South) indices combined to form the non‐negative PCC indices. For the cases of strong magnetic storms (Dst(peak )< −100 nT), the equivalent ASY‐H indices were found to agree well with reported (real) ASY‐H index values. The SRT PCC indices, furthermore, have been used in a PC‐based source function to derive equivalent values of the total ring current indices Dst (or SYM‐H) up to 1 h ahead of time. With integration of the source function throughout a decade (2009–2018) with no attachment to reported Dst values, the SRT equivalent Dst indices display close agreement with real Dst index values. The applied method could be used without modifications to generate PC index values and derived ASY‐H and Dst (or SYM‐H) index values in real‐time space weather applications.

Abstract . The present work examines the relations between Polar Cap (PC) indices and the 1-min SYM-H and hourly Dst indices characterizing total (symmetrical) magnetospheric ring current intensities with particular emphasis on possible space weather applications. Using real-time PC indices in a source function may provide gradient values for the ring current intensities characterized by the Dst or SYM-H indices. Upon integration during magnetic storm events the PC-based gradients may provide estimate of ring current index values up to one hour ahead. In a study of the strongest storm events in 2009-2018, the average correlation between real and corresponding equivalent SYM-H index values based on simulated real-time PC indices was 0.836. It is demonstrated that amplitude relations and timing differences for peak polar cap and ring current indices suggested in publications over the years and in a recent report from the International Standards Organisation (ISO) are not valid particularly for the stronger magnetic storms (Dst(peak)<-90 nT) and could be misleading.

1, 6, 7, and 8, I completely concur with reviewer's conclusion that "some record of this

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 (North) and PCS (South), in the version endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) is found in the commented publication, Janzhura and Troshichev (2011): Identification of the IMF sector structure in near-real time by ground magnetic data, Annales Geophysicae, 29, 1491–1500. Actually, the publication has served as 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. Figs. 1, 6, 7, and 8 display values derived by post-event calculations based on daily medians smoothed over 7 days centred on the day of interest. Figs. 2, 3, and 4 display observed values smoothed over 7 days, 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.

In the publication Troshichev et al. (2006) (https://doi.org/10.1029/2005JA011402) on the polar cap (PC) indices, PCN and PCS, an error was made by using components of the interplanetary magnetic field (IMF) in their geocentric solar ecliptic (GSE) representation instead of the prescribed geocentric solar magnetospheric (GSM) representation for calculations of index scaling parameters. The mistake has caused a trail of incorrect relations and wrong conclusions extending since 2006 up to now (2020) which should be discontinued, for instance, by issuing a corrigendum note from the authors. The present contribution explains the error and discusses in an extended example its consequences for one of the publications that have referred to the invalid scaling parameter set. Further investigations reported here of the PC index versions recommended by the International Association for Geomagnetism and Aeronomy (IAGA) indicate occurrences of similar problems in the present derivation of index scaling parameters.

The non-negative Polar Cap PCC index built from PCN (North) and PCS (South) indices correlates better with the solar wind merging electric field and is more representative for the total energy input from the solar wind to the magnetosphere and for the development of geomagnetic disturbances represented by the Kp index and ring current indices than either of the hemispheric indices. The present work shows that the ring current index, Dst, to a high degree of accuracy can be derived from a source function built from PCC indices. The integration of the PCC-based source function throughout the interval from 1992 to 2018 without attachment to the real Dst indices based on low latitude magnetic observations has generated equivalent Dst values that correlate very well (R = 0.86) with the real Dst index values, which are represented with a mean deviation less than 1 nT and an overall RMS deviation less than 13 nT. The precise correlation between the real and equivalent Dst values has been used to correct the PCC indices for saturation effects at high intensity disturbance conditions where the Dst index may take values beyond −100 nT. The relations between PCC and the ring current indices, Dst and ASY-H have been used, in addition, to derive the precise timing between polar cap convection processes reflected in the polar cap indices and the formation of the partial and total ring current systems. Building the ring current is considered to represent the energy input from the solar wind, which also powers auroral disturbance processes such as substorms and upper atmosphere heating. With current available PC indices, detailed and accurate SYM-H or Dst index values could be derived up to nearly one hour ahead of actual time by integration of the PCC-based source function from any previous quiet state. Thus, the PCC indices enabling accurate estimates of the energy input from the solar wind are powerful tools for space weather monitoring and for solar-terrestrial research.

(i.e. AARI#3 according to McCready and Menvielle, 2010) was based on using the interplanetary magnetic field components IMF By and Bz in their GSE representation instead of the prescribed GSM version. This unfortunate feature has never been published before in spite of many references to the publication and use of its scaling parameter illustrations, most recent in Figs. 2.3 and 2.9 of Troshichev (2017: Polar Cap magnetic activity (PC index) and space weather monitoring, ISBN: 978-3-8381-80120. On top, this publication holds in its Fig. 9.2 a reproduction of the IMF By and Bz components from Fig. 7 of Troshichev et al. (2006) (also presented in Fig. 1a of the commentary) without mentioning that it presents the GSE and not the GSM version.

A. Troshichev on "Comment on "Invariability of relationship between the polar cap magnetic activity

The Polar Cap (PC) indices are derived from the magnetic variations generated by the transpolar convection of magnetospheric plasma and embedded magnetic fields driven by the interaction with the solar wind. The PC indices are potentially very useful for Space Weather monitoring and forecasts and for related research. However, the PC index series in the near-real time and final versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) have been proven unreliable (Stauning, 2013, 2015, 2018a,b,c, 2020). Both versions include solar wind sector (SWS) effects in the calculation of the reference levels from which magnetic disturbances are measured. The SWS effects are caused by current systems in the dayside Cusp region related to the Y-component, BY, of the Interplanetary Magnetic Field (IMF). However, the IAGA-endorsed handling of SWS effects may generate unfounded PC index changes of up to 3 mV/m at the nightside away from the Cusp. For the real-time PCN and PCS indices, their cubic spline-based reference level construction may cause additional unjustified index excursions of more than 3 mV/m with respect to the corresponding final index values. Noting that PC index values above 2 mV/m indicate geomagnetic storm conditions, such unjustified contributions are considered to invalidate the IAGA-endorsed PC index series. The presentation shall include a description of alternative derivation methods shown to provide more consistent index reference levels for both final and real-time PC indices, to reduce their unfounded excursions, and to significantly increase their reliability (Stauning, 2016, 2018b,c). References. Stauning, P. (2020): The Polar Cap (PC) index: invalid index series and a different approach. Space Weather, 2020SW002442 (submitted). Stauning, P. (2013). Comments on quiet daily variation derivation in “Identification of the IMF sector structure in near-real time by ground magnetic data” by Janzhura and Troshichev (2011). Annales Geophysicae, 31, 1221-1225. https://doi.org/10.5194/angeo-31-1221-2013 . Stauning, P. (2015). A critical note on the IAGA-endorsed Polar Cap index procedure: effects of solar wind sector structure and reverse polar convection. Annales Geophysicae, 33, 1443-1455. https://doi.org/10.5194/angeo-33-1443-2015 . Stauning, P. (2016). The Polar Cap (PC) Index.: Derivation Procedures and Quality Control. DMI Scientific Report SR-16-22. Available at: https://www.dmi.dk/fileadmin/user_upload/Rapporter/TR/2016/SR-16-22-PCindex.pdf . Stauning, P. (2018a). A critical note on the IAGA-endorsed Polar Cap (PC) indices: excessive excursions in the real-time index values. Annales Geophysicae, 36, 621–631. https://doi.org/10.5194/angeo-36-621-2018 . Stauning, P. (2018b): Multi-station basis for Polar Cap (PC) indices: ensuring credibility and operational reliability. Journal of Space Weather and Space Climate, 8, A07. https://doi.org/10.1051/swsc/2017036 . Stauning, P. (2018c). Reliable Polar Cap (PC) indices for space weather monitoring and forecast