A schematic illustration of EMIC wave propagation process during storm (a) and non-storm (b) periods. The left part (a) shows that EMIC waves generated during storm period have relatively diverse source regions, resulting in varying propagation distances undergoing ionospheric wave attenuation effect. On the other hand, the right part (b) demonstrates that EMIC waves produced during non-storm periods arise from more limited source regions, which allows consistent distances undergoing ionospheric wave attenuation effect.