The Frequency‐Domain Characterization of Cosmic Ray Intensity Variations Before Forbush Decreases Associated with Geomagnetic Storms

Nonrecurrent geomagnetic storms caused by Coronal Mass Ejection (CME) can induce serious impacts on space- and ground-based equipment. However, these nonrecurrent are hard to predict since CMEs not periodic. Previous studies have shown that the variations of Cosmic Ray Intensity (CRI) before may forebode coming storm. But it is difficult extract cosmic ray flux a complex signal. In order identify precursory signal in CRI triggered CME, an ensemble self-adaptive time-frequency analysis method was proposed applied 65 occurred between 1998 2019. The results indicate signals successfully identified 43 45 storms, after excluding 20 accompanied ground level enhancement. addition, also found spectral density could reflect active condition, which lower during quiet period.