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Influence of interplanetary magnetic field (IMF) By polarity on the nightside electron discrete aurora, electron diffuse aurora, and ion aurora.

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Bibliographic Details
Title:	Influence of interplanetary magnetic field (IMF) By polarity on the nightside electron discrete aurora, electron diffuse aurora, and ion aurora.
Authors:	Zhou, Su¹ (AUTHOR), Luan, Xiaoli² (AUTHOR) luanxl@ustc.edu.cn, Lei, Jiuhou² (AUTHOR), Liu, Jing³ (AUTHOR), Zhu, Shengting² (AUTHOR), Huang, Fuqing² (AUTHOR), Ren, Dexin² (AUTHOR)
Source:	SCIENCE CHINA Earth Sciences. Jun2026, Vol. 69 Issue 6, p2206-2216. 11p.
Subject Terms:	Interplanetary magnetic fields, Auroras, Electron emission, Solar wind, *Magnetosphere
Geographic Terms:	Southern Hemisphere
Abstract:	Nightside auroras are an important manifestation of the solar wind-magnetosphere-ionosphere coupling, and their spatial distribution and intensity variations are crucial for understanding magnetospheric dynamics. In this work, we investigate the influence of the IMF By component on the nightside auroras using the DMSP/SSJ in-situ data from 2000 to 2023 in the Southern Hemisphere. Unlike previous studies, which primarily rely on far ultraviolet emission data, our analysis enables the distinction between electron discrete aurora, electron diffuse aurora, and ion aurora. We find that a positive IMF By can shift the peak energy flux of discrete aurora toward the post-midnight sector and to lower latitudes. This characteristic is likely associated with the displacement of magnetic field line footpoints induced by the penetration of IMF By into the closed field lines. The effects of IMF By on the nightside auroras depend on magnetic local time (MLT) sectors. For the electron discrete aurora, the most significant enhancement associated with positive IMF By occurs near 00–01 MLT. This is likely associated with the interhemispheric field-aligned current (IHFAC) that strengthens the downward electron energy flux as well as the electron discrete aurora. An MLT transition region, where the IMF By effect reverses, is identified for each auroral type. The exact location of this transition depends on the IMF Bz and By polarities. From the transition region toward the dawn sector, each type of aurora is enhanced during the positive IMF By, as compared with negative IMF By. In contrast, the effect of IMF By is reversed toward the dusk sector. These patterns are similar under both the northward and southward IMF Bz conditions. These results suggest that the IMF By asymmetrically penetrates the closed field lines, thereby altering the magnetospheric topology and modulating the spatial distribution and intensity of these auroral types on the nightside. [ABSTRACT FROM AUTHOR]
Database:	Energy & Power Source

Description
Abstract:	Nightside auroras are an important manifestation of the solar wind-magnetosphere-ionosphere coupling, and their spatial distribution and intensity variations are crucial for understanding magnetospheric dynamics. In this work, we investigate the influence of the IMF By component on the nightside auroras using the DMSP/SSJ in-situ data from 2000 to 2023 in the Southern Hemisphere. Unlike previous studies, which primarily rely on far ultraviolet emission data, our analysis enables the distinction between electron discrete aurora, electron diffuse aurora, and ion aurora. We find that a positive IMF By can shift the peak energy flux of discrete aurora toward the post-midnight sector and to lower latitudes. This characteristic is likely associated with the displacement of magnetic field line footpoints induced by the penetration of IMF By into the closed field lines. The effects of IMF By on the nightside auroras depend on magnetic local time (MLT) sectors. For the electron discrete aurora, the most significant enhancement associated with positive IMF By occurs near 00–01 MLT. This is likely associated with the interhemispheric field-aligned current (IHFAC) that strengthens the downward electron energy flux as well as the electron discrete aurora. An MLT transition region, where the IMF By effect reverses, is identified for each auroral type. The exact location of this transition depends on the IMF Bz and By polarities. From the transition region toward the dawn sector, each type of aurora is enhanced during the positive IMF By, as compared with negative IMF By. In contrast, the effect of IMF By is reversed toward the dusk sector. These patterns are similar under both the northward and southward IMF Bz conditions. These results suggest that the IMF By asymmetrically penetrates the closed field lines, thereby altering the magnetospheric topology and modulating the spatial distribution and intensity of these auroral types on the nightside. [ABSTRACT FROM AUTHOR]
ISSN:	16747313
DOI:	10.1007/s11430-025-1927-7