AUTHOR=Troshichev O. A. 

TITLE=PC index as a ground-based indicator of the solar wind energy incoming into the magnetosphere: (1) relation of PC index to the solar wind electric field EKL

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2022.1069470

DOI=10.3389/fspas.2022.1069470

ISSN=2296-987X

ABSTRACT=<p>The polar cap magnetic activity <italic>PC</italic> index was approved by IAGA as a proxy for energy that enters into the magnetosphere during solar wind-magnetosphere coupling (<xref ref-type="bibr" rid="B41">IAGA Resolutions, 2013</xref>; <xref ref-type="bibr" rid="B40">IAGA Resolution, 2021</xref>). The paper summarizes experimental results attesting the validity of this <italic>PC</italic> index essence. The following issues are examined: the <italic>PC</italic> index derivation method, making allowance for regular and irregular variations of ionospheric conductivity; relationships between the <italic>PC</italic> index and solar wind electric field (<italic>E</italic><sub><italic>KL</italic></sub><italic>)</italic> and factors controlling response of <italic>PC</italic> index to the <italic>E</italic><sub><italic>KL</italic></sub> field alterations; relation of <italic>PC</italic> index to the magnetospheric field-aligned currents (FAC) and to solar wind dynamic pressure pulses (Pdyn). The <italic>PC</italic> index alterations in course of 23/24 solar activity cycles have been analyzed in relation to various solar wind parameters and the conclusion was made that linear link between the <italic>PC</italic> index and solar wind electric field <italic>E</italic><sub><italic>KL</italic></sub> remained valid irrespective of solar activity cycle. New ideas concerning (1) the nature of occasional differences between the <italic>PC</italic> indices in summer and winter polar caps and (2) two simultaneously acting mechanisms of the solar wind influence on the magnetosphere (Dungey and Tverskoy concepts) are discussed, as a result of the <italic>PC</italic> index application. It is emphasized that the ground-based <italic>PC</italic> index ensures a permanent on-line information on geoefficiency of the solar wind impact on the magnetosphere and, correspondingly, on the varying geophysical situation.</p>