# Correlation Study of Auroral Currents with External Parameters During 10-12 October 2024 Superstorm
## 4 Discussion
### Correlation Analysis  
Figures 2 and 3 show that the timing of the maximum FACs and PEJs, as well as the moment they reached the lowest latitude, exhibited differences in the four local times and two hemispheres. This suggests that the external parameters most influencing FACs and PEJs vary by local time and hemisphere. As outlined in the Introduction section, previous studies have shown that factors such as Em, Pd, IMF By, Bz, and Dst can affect the density and latitude of polar currents during storm periods. Therefore, we performed a Spearman rank correlation analysis between the peak FAC densities/latitudes and external solar wind parameters and geomagnetic indices. The \(p\)-value in the context of Spearman's rank correlation helps assess whether the correlation is likely to be real or if it might be due to random chance. A smaller \(p\)-value generally below 0.05 (a commonly accepted significance level in the field of study) generally indicates stronger evidence for a true relationship. There were 62 events, respectively, in the dusk and dawn sectors of the Northern and Southern Hemispheres, while there were 61 events in the daytime and nighttime sectors of the two hemispheres. With the exception of IMF By, the \(p\)-values for the other IMF and geomagnetic parameters were generally below 0.05, indicating relatively significant non-zero correlations. The reason for the weak By correlation is that geomagnetic storms are mainly driven by southward IMF Bz, which can drive rapid and large-scale reconnection between the IMF and the Earth's magnetic field, resulting in significant auroral currents. During geomagnetic quiet periods, the influence of IMF By becomes more prominent [(20; 21)]. The effects of the solar wind mass density and velocity are considered separately, which both contribute to Pd. Averages of the external parameters were taken within 10-20 min before Swarm detections. The choice of 10-20-min averages was made to accommodate the time delay from the bow shock to the ionosphere. Specifically, we used IMF data at the bow shock and computed the solar wind and IMF parameters by averaging the values over a 10 to 20 min interval prior \begin{table}
\begin{tabular}{l c c} \hline
**NH (SH)** & **PEJs Density [A/m]** & **PEJs MLat** [\({}^{\circ}\)] \\ \hline Dusk & 0.51 (0.56) & 61.2 (\(-62.3\)) \\ Dawn & 0.87 (0.64) & 63.0 (\(-63.1\)) \\ Daytime & 0.46 (0.59) & 71.3 (\(-69.1\)) \\ Nighttime & 0.46 (0.42) & 64.6 (\(-64.9\)) \\ \hline \end{tabular}
\end{table} 
Table 2: The average PEJ density and MLat during the 12 to 48 storm-time period for four local time sectors. For the dusk sectors, eastward PEJs are provided, while for the dawn, daytime, and nighttime sectors, the westward PEJs are presented. Values outside (inside) parentheses correspond to the Northern (Southern) Hemisphere (NH, SH). to the observed FACs, in line with our previous work [20; 21; 22]. [PERSON] et al. (2002) [23] considered a typical delay of 15 min for the development of FACs, from the magnetopause to the ionospheric response. [PERSON] et al. (2018) [24] averaged the solar wind and IMF parameters over the 20 min preceding the corresponding Swarm/CHAMP measurements. [PERSON] et al. (2023) [25] employed 1 h averaged IMF components from 1981 to 2019 to investigate the effect of IMF Bx on the AL index. The averaging time window employed in the current study aligns well with these earlier works. Figure 4 shows the correlation coefficients between the peak density of the upward and downward FACs and different external parameters, like the merging electric field, solar wind dynamic pressure, IMF By and Bz components, Dst index, and solar wind mass density and velocity. The left and right panels represent the Northern and Southern Hemispheres, respectively. The top panel corresponds to the dusk and dawn sectors, while the bottom panel corresponds to the daytime and nighttime sectors. Different colors represent different polarities of FACs (upward or downward) in different local times.