# Interplanetary Magnetic Field Bx Effect on Field-Aligned Currents in Different Local Times
## 4 Discussion
This hemispheric variation is attributed to magnetic field antiparallel reconnection, where the polarity of IMF Bx significantly influences the reconnection process between the solar wind IMF and the geomagnetic field in the two hemispheres. Previous studies by [PERSON] (1981) [25] and [PERSON] et al. (2014) [17] suggest that a negative IMF Bx favors magnetic tail reconnection in the NH, which generates greater magnetic tension on open field lines and enhances magnetospheric boundary currents. In contrast, positive IMF Bx favors reconnection in the SH, thereby enhancing boundary currents in that hemisphere. The resulting increase in magnetospheric electric fields, particularly near noon, can enhance FACp intensity. These findings are consistent with the theoretical background of our research. [PERSON] et al. (2018) [15] also observed that, under negative Bx conditions, R1 FACs in the NH are stronger, while under positive Bx conditions, R1 FACs in the SH are stronger. These observations align with our results. However, unlike in our study, [PERSON] et al. did not categorize FACs based on PEJ polarity, nor did they differentiate between FACp and FACe. Moreover, they did not analyze the data across four distinct local time sectors. The influence of IMF Bx on equatorial FACe is generally weaker compared to its impact on FACp (except in the noon sector, as shown in Figure 4). This difference arises from the distinct sources of FACp and FACe in the magnetosphere. Region 1 currents, located on the polar side, originate at the magnetopause and are more sensitive to the solar wind and IMF, while Region 2 FACs on the equatorward side originate from the inner magnetosphere and are less directly influenced by the solar wind and IMF. During the noon sector, the effect of IMF Bx on FACe is more pronounced than in other local time sectors, but its polarity effect is opposite to that on FACp. In the noon sector, where westward PEJ dominates, FACe in the NH is stronger when IMF Bx < 0, while in the SH, the opposite trend is observed. [PERSON] et al. (2024) [11] found that westward PEJ in the NH is stronger when IMF Bx < 0, while the SH exhibits the opposite IMF Bx polarity dependence. The response of FACe to IMF Bx resembles that of PEJ, which indicates a close relationship between equatorial FACe and PEJ during the noon sector. The IMF Bx effect on the noontime and midnight PEJs is more obvious in summer, when the ionospheric conductivity is larger due to increased solar illumination. This can be explained by the following scenario: during periods when IMF Bx < 0 (Bx > 0), the reconnection site tends to occur around the northern (southern) magnetotail lobe, facilitating antiparallel reconnection between the earthward (sunward) IMF Bx and the northward geomagnetic field. In summer, the magnetotail shifts closer to the Sun, creating a geomagnetic configuration that favors lobe reconnection. In comparison to the day-midnight sector, the influence of IMF Bx on FACp at dawn is more pronounced during the local winter than during the local summer. Specifically, throughout winter in the NH, a negative IMF Bx leads to a stronger westward PEJ than a positive IMF Bx. In contrast, throughout winter in the SH, a positive IMF Bx results in a stronger westward PEJ compared to a negative IMF Bx. This discovery corresponds with the research by [PERSON] et al. (2023) [26], which showed that during NH winter, IMF Bx < 0 enhances the AL index, while IMF Bx > 0 suppresses it under similar driving conditions. Additionally, [PERSON] et al. (2011) [27] observed that stations within the 00:00-06:00 MLT range most pronouncedly influenced the AL index. [PERSON] et al. (2018) [15] further revealed that total currents attained their peak levels during the late-night hours between 03:00 and 04:00 MLT, particularly when the IMF pointed southward throughout all seasons. This supports the idea that the wintertime preference of FACp aligns with the AL index peak in the dawn sector. [PERSON] et al.