Frequency?Dependent Modulation of Whistler?Mode Waves by Density Irregularities During the Recovery Phase of a Geomagnetic Storm

Density irregularities near the plasmapause are commonly observed and play an important role in whistler-mode wave excitation propagation. In this study, we report a frequency-dependent modulation event of waves by background density during geomagnetic storm. Higher-frequency whistler (near , where is equatorial electron cyclotron frequency) trapped trough regions due to small refractive index parallel direction, while lower-frequency (below ) crest maximum along direction. addition modulation, also find that, quantitatively, amplitude higher- (lower-) frequency anti-correlated (correlated) with relative plasma variation. Our study suggests importance irregularity dynamics controlling intensity, thus radiation belt dynamics.