The PC Index Variations During 23/24 Solar Cycles: Relation to Solar Wind Parameters and Magnetospheric Disturbances

Abstract

The polar cap magnetic activity PC index is regarded as indicator of the solar wind energy that enters into the magnetosphere during the solar wind‐magnetosphere coupling (Resolutions of XXII IAGA Assembly, 2013). This study presents the results of statistical analysis of relationships between the yearly values of PC index and such indicators as the magnetic activity indices (AE and Dst), the solar wind parameters (velocity Vsw, density Nsw, dynamic pressure Pdyn, vertical interplanetary magnetic field (IMF) component Bz, total IMF field |B|, electric field EKL), and the solar activity parameters (sunspot number, coronal mass ejections, stream interaction regions) in course of 23–24 solar cycles. It is shown that the yearly values of the quiet daily curve magnitude (which serves as a level of reference in estimation of the PC index value) changed during 1998–2019 in remarkable agreement with variation of the Solar UV irradiation (150–200 nm) absorbed in the Earth's ionosphere. The yearly values of PC index perfectly correlate with the yearly values of Vsw and |B| and their product electric field EKL, as well as with the yearly values of AE and Dst indices testifying that PC index serves as the ground‐based indicator of the solar wind energy input into the magnetosphere. The yearly values of EKL, PC, AE, Dst correlate with the total IMF field |B| much better that with the IMF Bz component, testifying that efficiency of the solar wind impact on the magnetosphere is defined by the total IMF value, in contrast with Dungey's concept of reconnection.

The Use of Invalid Polar Cap South (PCS) Indices in Publications

“…Figure 2 of Troshichev et al. (2021) presents the mean yearly values of PCN and PCS indices. Such yearly mean PCN and PCS values should be equal to within a few percent since both PC index versions are calibrated against the common merging electric field, E KL ( E M ).…”

“…">Troshichev et al. (2021). The abstract states that “ The polar cap magnetic activity PC index is regarded as indicator of the solar wind energy that enters into the magnetosphere during the solar wind – magnetosphere coupling (Resolutions of XXII IAGA Assembly, 2013) ”.Further, the introduction in Section 1 states: “ Taking into account this distinctive feature of the PC index, the IAGA approved PC index as ‘‘a proxy for energy that enters into the magnetosphere during solar wind – magnetosphere coupling’’ (Resolution of XXII IAGA Assembly, 2013) ”.The acknowledgments section states: “ The 1‐min PCS and PCN indices calculated by the unified method in AARI and in the Space Institute of the Danish Technical University (DTU) are published on‐line at site: http://pcindex.org/ ”.…”

Auroral Ionosphere Model with PC Index as an Input

“…The comparative data analysis of PC index and the Newell's coupling function with the integrated auroral power of particle precipitation obtained from the Polar satellite shows that the PC index correlates with the magnitude of auroral power much better (the correlation coefficient R PC ∼0.76−0.87, depending on the time delay) than the Newell's coupling function (R N ∼0.46−0.82), and especially in the real-time mode R PC = 0.76 versus R N = 0.46 [32]. Furthermore, it was shown that PC index has a high correlation with basic indices of magnetospheric disturbances AL and Dst [24,25,33].…”

“…In order to improve the accuracy of AIM-E model when simulating highly variable periods during geomagnetic storms and substorms, we use OVATION-Prime model with modified parameterization, where the solar wind-based Newell's coupling function (N) is changed for the ground-based Polar Cap (PC) index, responding in the real-time to the solar wind energy input into the magnetosphere [25]. Hereinafter, we will use the designations OVATION-Prime (PC) and AIM-E (PC) to reflect the modification of the models switching to the PC input.…”

Reply to Comment by Stauning on “The PC Index Variations During 23/24 Solar Cycles: Relation to Solar Wind Parameters and Magnetic Disturbances”

“…It should be emphasized once more that the values shown in columns 1-3 and 4-6 are based on data of the preliminary PCS indices, which were presented at site http://pcindex.org up to December 2021. The daily mean values of PCN and PCS indices, estimated by the hourly median quantities, used in analysis (Troshichev et al, 2021), as well as the daily mean values, estimated by the hourly mean quantities, are available at the web portal http://geophys.aari.ru/PCspaceweather.…”