Search for: All records

Abstract A Van Allen Probes observation of a high‐density duct alongside whistler‐mode wave activity shows several distinctive characteristics: (a)—within the duct, the wave normal angles (WNA) are close to zero and the waves have relatively large amplitudes, this is expected from the classic conceptualization of ducts. (b)—at L‐shells higher than the duct's location a large “shadow” is present over an extended region that is larger than the duct itself, and (c)—the WNA on the earthward edge of the duct is considerably higher than expected. Using ray‐tracing simulations it is shown that rays fall into three categories: (a) ducted (trapped and amplified), (b) reflected (scattered to resonance cone and damped), and (c) free (non‐ducted). The combined macroscopic effect of all these ray trajectories reproduce the aforementioned features in the spacecraft observation. 

Abstract Lightning‐induced Electron Precipitation (LEP) is a known process of electron loss in the Earth's radiation belts. An LEP event progresses with Very Low Frequency (VLF) radio wave radiation from lightning, trans‐ionospheric propagation, and wave‐particle gyroresonance interaction with energetic radiation belt electrons. Pitch angle scattered electrons then precipitate onto the ionosphere, allowing detection using VLF remote sensing using high power transmitters. The relative importance of LEP events as a radiation belt electron lifetime driver has heretofore been unclear. We build off a massive database of LEP events observed within the continental US (CONUS) by a network of VLF receivers. For each observed LEP event, based on the characteristics of the ionospheric disturbance, we apply a suite of models to estimate the total number of precipitating electrons, which we can then sum up over all LEP events to quantify lightning's contribution within CONUS. We find that LEP events within CONUS appear to be capable of removing a substantial fraction (up to 0.1%–1%) of radiation belt electrons between 33 and 1,000 keV, and may have stronger contributions to radiation belt losses than earlier estimates.