# Interplanetary Magnetic Field Bx Effect on Field-Aligned Currents in Different Local Times
## 4 Discussion
(2023) [26] explained that the IMF Bx component can influence the configuration of the nightside magnetosphere, causing the auroral current system to shift northward or southward, depending on whether IMF Bx is negative or positive. Specifically, during periods of significant negative dipole tilt (i.e., NH winter), when the plasma sheet is located beneath its usual position, a negative IMF Bx can induce a shift in the current sheet toward the central plane, restoring symmetry and intensifying auroral activity. A similar effect occurs in the SH winter, characterized by a large positive dipole tilt and IMF Bx > 0. Another factor that explains why IMF Bx primarily affects the dawnside PE] during winter is its influence on auroral precipitation. According to [PERSON] et al. (2002) [16], auroral power in the NH is greater when IMF Bx is negative compared to when it is positive, while the SH exhibits the opposite trend. This dependence of auroral intensity on IMF Bx was further corroborated by [PERSON] et al. (2014) [17]. These findings could help to explain why IMF Bx has a stronger impact on PEJ during the local winter than during the local summer. We also observed that the influence of IMF Bx on the location of FACs is primarily concentrated on the day-night side of the magnetosphere. Specifically, during the noontime and midnight sectors, when the westward auroral electrojet is dominant, FACs are located at higher latitudes in the NH for positive IMF Bx compared to those when it is negative. Conversely, the SH exhibits the opposite trend. For noontime FACs, where the eastward auroral electrojet dominates, this polarity dependence of IMF Bx is reversed. This observation aligns with the latitudinal variation in the auroral electrojet for IMF Bx polarity ([PERSON] et al., 2024 [14]), suggesting that the observed changes in FAC location are linked to shifts in the position of the auroral oval, primarily driven by variations in the site of magnetic reconnection. [PERSON] et al. (2013) [28] reported systematic north-south asymmetries arising from the interaction between specific IMF radial directions and the Earth's magnetic field configuration. As a result, fluctuations in IMF Bx influence the latitudinal distribution of FACs in the ionosphere by altering the location of magnetic reconnection. Additionally, we observed a relationship between FAC density and latitude in response to IMF Bx: for a given IMF Bx polarity, stronger FACp appears at lower latitudes. This suggests that when a specific IMF Bx polarity enhances magnetic reconnection, more energy is transferred into geospace, which strengthens FACs, expands the polar cap, and shifts the auroral oval equatorward. The IMF Bx direction also influences the locations of magnetic reconnection between the Earth's magnetosphere and IMF. For southward IMF Bx, the reconnection is more likely to occur on the dayside, whereas for IMF Bx > 0, reconnection typically takes place in the magnetotail lobe region. Although FAC strength and latitude vary with different IMF Bx orientations, our study found an increased occurrence of quiet-time FAC events during the observation period. Furthermore, the trend in \(\Delta\)Em remained consistent (Figure 5d), with Em also reflecting the influence of IMF Bx. As a result, the direction of IMF Bx did not alter the fundamental conclusions of our study. One can observe that the effect of IMF Bx differs from that of IMF By in terms of local time and seasonal variations. The effect of IMF Bx on FACs density and latitude is most pronounced in the noon-midnight sector and the dawnside, whereas IMF By has a significant influence at all local times. The impact of IMF Bx on FAC density is stronger on the day-night side during summer than in winter, while on the dawnside, it is stronger in winter than in summer. In contrast, the influence of IMF By on FAC density is generally stronger in summer than in winter.