Analysis of ULF waves reveals distinct characteristics before dipolarization in the near-Earth magnetotail, suggesting significant implications for events.
We studied the characteristics of ultra‐low‐frequency (ULF) waves associated with dipolarization in the near‐Earth plasma sheet for substorms and pseudosubstorms, employing superposed epoch analysis of data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft. We find exponential intensification of ULF waves before dipolarization for both substorms and pseudosubstorms, highlighting Pi2 waves' appearance before Pi1 waves. After rapid growth, the high‐frequency portion of the Pi2 waves and the Pi1 waves in a tailward region for pseudosubstorms are notably weaker and decrease faster than those for substorms. These results suggest that instabilities related to high‐frequency Pi2 and Pi1 waves are essential for a full‐fledged substorm and auroral poleward expansion.
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Kasonsuwan et al. (2026) studied this question.
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