Statistical Survey of Cosmic Noise Absorption in Conjunction With Plasma Wave Measurements

Abstract

Using a decade of observations from the Canadian Geospace Observatory Riometer Network (GO‐RIO), we selected an east‐west subset of stations near to classify cosmic noise absorption (CNA) (a proxy for enhanced D‐region ionization) into two morphologies, simultaneous and drifting, based on the relative timing of signals across the chain. We then examined the magnetospheric context using in situ measurements from the Van Allen Probes and Time History of Events and Macroscale Interactions during Substorms (THEMIS) in conjunction with ionospheric absorption measured by ground‐based instruments. To capture typical behavior, we compared median power spectral density in the lower band chorus range between elevated absorption cases and quiet times and we examined electron energy spectra from the Van Allen Probes' Magnetic Electron Ion Spectrometer. Relative to the quiet times control group, both morphologies showed enhanced lower‐band chorus power within 0.1–0.5 electron gyro‐frequency and elevated electron flux concentrated in the tens of keV range. These signatures are consistent with plasma‐sheet injections that supply free energy for whistler‐mode chorus growth and subsequent pitch angle scattering into the loss cone. The combined observations support a coherent picture in which chorus‐driven pitch‐angle diffusion produces energetic electron precipitation, which enhances D‐region ionization and is observed as increased CNA. Moreover, the drifting absorption events are associated with slightly stronger lower‐band chorus emissions that exhibit greater temporal persistence, suggesting that these waves are maintained by more stable or spatially extended source regions.