Following the Path of QPPs: Solar Flare Oscillations from the Corona through the Heliosphere to Earth's Ionosphere

Quasi-periodic pulsations (QPPs) are a common feature in solar flare emissions, yet their physical origins remain debated. In this study, we conduct a comprehensive multi-wavelength analysis of QPPs in sixteen solar flares (one X-class and fifteen M-class) observed during Solar Cycle 25. We utilize data from GOES/XRS (soft X-ray), \textit{Fermi}/GBM (soft and hard X-ray), LOFAR (radio), and VLF/SID (ionospheric disturbances) to systematically characterize QPPs across thermal and non-thermal energy ranges. Fast-varying oscillatory components are extracted from flare light curves using detrending techniques, and periods are identified via wavelet analysis. We investigate the temporal and spectral relationships between QPPs at different wavelengths, including their association with coronal mass ejections (CMEs) and various radio burst types. Our results reveal that QPPs typically exhibit multiple periods, with dominant periodicities in the 40–70 s range, and show strong correlations ($\ge$~0.5) between thermal and non-thermal emissions in the impulsive phase of flares. The timing analysis indicates that X-ray QPPs generally precede radio signatures, suggesting a causal link through electron acceleration and magnetic reconnection processes. Additionally, we find that QPPs are frequently observed in both soft and hard X-rays and at radio wavelengths, and that their occurrence is often accompanied by CMEs and sudden ionospheric disturbances. These findings support the interpretation that QPPs are driven by periodic dynamics of non-thermal electron injection, modulated by magnetohydrodynamic (MHD) wave modes and magnetic reconnection. This multi-instrument approach provides new insights into the mechanisms underlying QPPs and their impact on the near-Earth environment.