Comment on “The Use of Invalid Polar Cap South (PCS) Indices in Publications” by Stauning

Abstract

The polar cap magnetic activity PC index is calculated by magnetic data from near-pole stations Thule in Greenland (PCN index) and Vostok in Antarctic polar cap south (PCS index). Before 2011 the PCN index was calculated in Danish Meteorological Institute (DMI) either by the official DMI method (Vennerstrom, 1991) or by the solar rotation weighted (SRW) method described later in Stauning (2011). The PCS index was calculated in Arctic and Antarctic Research Institute (AARI) with use of the "unified" method put forward in (Troshichev et al., 2006; thereafter TJS2006) for derivation of both, PCN and PCS, indices. The comprehensive analysis of these competitive methods has been fulfilled by IAGA Division V-DAT in 2009-2010 and the "unified" TJS2006 method has been recommended, as the best, for the IAGA endorsement (McCreadie & Menvielle, 2010). In 2011 the Space Institute of the Danish Technical University (DTU-Space) became responsible for magnetic observations at Thule station and in 2013 the PC index, derived by the "unified" TJS2006 method, was approved by IAGA as a new index characterizing the solar wind energy input into the magnetosphere (IAGA Resolution no. 3, 2013). In line with agreement between the AARI and DTU-Space the PCN and PCS indices for previous years were recalculated in 2014 with application of the "unified" PC derivation method approved by IAGA.According to the IAGA rules, all indices obtained by data of current magnetic observations are considered as "preliminary" indices. They should be recalculated afterward making allowance for all possible faults of observational, technical and computer-assisted origin, to produce the "definitive" indices, which will be valid for ever. This work was fulfilled in 2021 in AARI and DTU Space with use of the restructured and harmonized code (Nielsen & Willer, 2019). Comparison of the provisional and definitive PCN and PCS indices for 22 years has demonstrated perfect conformity between the appropriate PCN and PCS indices. As a result, the definitive PCN and PCS indices were ultimately approved by IAGA and the PC index was recommended for use by international scientific community (IAGA Resolution no. 2, 2021). The definitive PCN and PCS indices are presented at site: http://pcindex.org.

Northern and Southern Hemisphere Polar Cap Indices: To What Extent Do They Agree and to What Extent Should They Agree?

“…The first dealt with the generality of the procedures applied to PCS (Lukianova, 2007; Troshichev et al., 2007), the point being that if the corrections are too tailored to solving existing anomalies, they may well not apply to future data. The second related to times about outstanding differences between the two indices (Stauning, 2022a, 2022b; Troshichev et al., 2022b). It is certainly true that considerably greater agreement between PCS and PCN exists in the IAGA‐approved version of the data than used to be the case before application of the unified method, to the extent that remaining differences between PCS and PCN may well be real and it could be the expectation that they should be the same that may be in error.…”

Universal Time variations in the magnetosphere

“…All the IAGA-endorsed definitive data have been regenerated by this unified method, a task that was completed in 2021 and various anomalies resolved. There has been debate in the literature about outstanding anomalies (Stauning, 2022;Troshichev et al, 2022) but our investigations show that the currently-available definitive data give considerably greater agreement between PCS and PCN than used to be the case before application of the unified method, to the extent that remaining differences between PCS and PCN may well be real and it is the expectation that they should be the same that may be in error (For example, lobe stirring reconnection usually influences one polar cap but not the other).…”

Lockwood_PCIndex_R1

“…The first dealt with the generality of the procedures applied to PCS (Lukianova, 2007;, the point being that if the corrections are too tailored to solving existing anomalies, they may well not apply to future data. The second related to times about outstanding differences between the two indices (Stauning, 2022a(Stauning, , 2022bTroshichev et al, 2022a).…”