Statistical Characteristics of Solar Cycle Distribution of N-S Asymmetry for the Source Locations of Super Geomagnetic Storms (Dst≤-250 nT) during 1932-2018

After studying solar cycle distribution of N-S asymmetry of the source locations of super geomagnetic storms (SGSs: Dst250 nT) during 1932-2018, we found that during ascending phases, SGS source locations were predominantly in the northern hemisphere (NH), exhibiting significant N-S asymmetry. For the SGSs in the descending phases, source locations of the SGSs dominated in the NH and N-S asymmetry was only significant in the western hemisphere. For the period from 1932 to 2018, the source locations of SGSs were predominantly in the NH, and the N-S asymmetry was significant. The cumulative numbers of SGSs originating from the two hemispheres were strongly anticorrelated during the ascending phases, descending phases, and the entire period from 1932 to 2018. For the source locations of SGSs with different intensities, significant N-S asymmetries were observed in the source location distribution. Specifically, for all SGSs, SGSs with −400nT<Dst≤−300nT, and SGSs with Dst≤−300nT, the NH exhibited a higher number of events compared to the SH, indicating a dominance of SGSs in the NH. From the perspective of the evolution of N-S asymmetry with solar cycle, the source locations of the SGSs always dominated in the NH during the ascending phases. However, during solar cycles 17-19 and 21, the source locations of the SGSs dominated in NH, while during solar cycles 20, 22 and 23 the source locations of the SGSs dominated in the SH. From the perspective of N-S asymmetry for Solar Cycles 17 to 23, solar activity across the two hemispheres is largely balanced. However, the solar activities manifested by CMEs that can trigger SGSs during Solar Cycles 17 to 23 were predominantly in the NH. Therefore, factors beyond solar activity, such as the propagation of the CMEs from the Sun to the Earth, likely contribute to the observed N-S asymmetric distribution of the source locations of SGSs.