The prevalence and significance of wave cross-scale coupling in the Earth’s magnetosphere: observations from the Van Allen Probes

We present a novel technique for detecting cross-scale coupling of plasma waves in Earth’s radiation belts through the use of the Van Allen Probes (RBSP) filterbank data products. We find that intermediate frequency (18.5 Hz–4.85 kHz) waves modulated at low frequencies (0.7–3.0 Hz) are more common in the magnetosphere than was previously understood. Our results show the modulations are more frequent on the dawn side, between magnetic local times (MLTs) of ∼2–14, with peak occurrence at L values of 5–6. The modulation peak occurrence moves from the dayside to pre-dawn as geomagnetic activity levels increase. As the modulated wave frequency increases, the occurrence probability moves from pre-dawn to noon. These results may have important implications for wave-particle interactions and radiation belt dynamics because modulated waves can more efficiently scatter electrons than non-modulated waves.