Abstract
Abstract. The International Association of Geomagnetism and Aeronomy (IAGA) has recently endorsed a new Polar Cap (PC) index version to supersede the previous seven different versions of the PCN (North) index and the five different PCS (South) index versions. However, the new PC index has some adverse features which should be known and taken into account by users of the index. It uses in its derivation procedure an "effective" quiet day level (QDC) composed of a "basic" QDC and an added solar wind sector term related to the azimuthal component (By) of the interplanetary magnetic field (IMF). The added IMF By-related terms may introduce unjustified contributions to the PC index of more than 2 index units (mV m−1). Furthermore, cases of reverse convection during strong northward IMF Bz (NBZ) conditions included in the database for calculation of index coefficients can cause unjustified index enhancements of 0.5–1 mV m−1 during calm conditions, reduction of index values by more than 20 % during disturbed conditions, and inconsistencies between index coefficients and index values for the northern and southern polar caps. The aim here is to specify these adverse features and quantify their effects, and to suggest alternative steps for future modifications of the index procedure.
Highlights
The Polar Cap (PC) index concept was suggested by Troshichev and Andrezen (1985) and developed roughly into its present form by Troshichev et al (1988, 2006)
The concept from TJS2006 is violated in the new index procedure by the addition of an interplanetary magnetic field (IMF) By-related solar wind sector (SS) term derived from the daily median of all data, quiet as well as disturbed, to the basic quiet day curve (QDC) derived from quiet data samples only
The question is : what are the consequences of using the “effective” QDC procedure (Appendix_AF) for the PC index calculations? Here, we use the data published by the authors of the procedure to derive the additions to the PCN index values from the solar wind sector terms
Summary
The Polar Cap (PC) index concept was suggested by Troshichev and Andrezen (1985) and developed roughly into its present form by Troshichev et al (1988, 2006). P. Stauning: A critical note on the IAGA-endorsed Polar Cap index procedure describe a former PC index version developed at AARI. Stauning: A critical note on the IAGA-endorsed Polar Cap index procedure describe a former PC index version developed at AARI In the documentation PC_index_description_main_document.pdf found at the Space DTU (2014) ftp site ftp: //ftp.space.dtu.dk/WDC/indices/pcn/PC_index_IAGA_ endorsement_documentation/, reference is made to the following sources for more extended descriptions of the PC index procedures: Troshichev et al (2006); Janzhura and Troshichev (2008, 2011); Troshichev and Janzhura (2012). Alternative steps in the index procedure are suggested for future modifications of the IAGA-endorsed procedure
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