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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 33, issue 11
Ann. Geophys., 33, 1443–1455, 2015
https://doi.org/10.5194/angeo-33-1443-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 33, 1443–1455, 2015
https://doi.org/10.5194/angeo-33-1443-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 30 Nov 2015

Regular paper | 30 Nov 2015

A critical note on the IAGA-endorsed Polar Cap index procedure: effects of solar wind sector structure and reverse polar convection

P. Stauning P. Stauning
  • Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark

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.

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Short summary
Polar Cap (PC) index values are derived from polar magnetic variations and are important for the scaling of solar-terrestrial relations. The International Association of Geomagnetism and Aeronomy (IAGA) has recently endorsed a new PC index version to supersede the many previous index versions. However, the new PC index procedure has some adverse features which should be known and taken into account by users of the index. These features are discussed and alternative procedures are suggested.
Polar Cap (PC) index values are derived from polar magnetic variations and are important for the...
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