Auroral Asymmetry Associated With the South Atlantic Anomaly

The South Atlantic anomaly (SAA) exerts a weakening effect on magnetic field strength on Earth, however, little is known of its effect on the auroral spatial distribution and temporal evolution. Using Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager ultraviolet data spanning 2016–2023, we investigated the impact of the SAA on auroral asymmetries. The SAA amplified the inherent north–south hemispheric asymmetry by reducing the local south/north intensity ratios, modified the semiannual variations through a seasonally persistent suppression, and modulated the dawn–dusk asymmetries by attenuating the southern hemisphere intensity while enhancing the northern hemisphere dawnside intensity. The SAA-induced auroral asymmetries persisted across geomagnetic conditions but became more distinguishable during active periods. Therefore, the SAA acts as a local perturbation and global modulator of auroral precipitation patterns. This work provides new insights into auroral behavior on Earth and can be extended to other planetary bodies with nondipolar or weak magnetic field configurations.