Lightning-induced coupling of the radiation belts to geomagnetically conjugate ionospheric regions.

摘要

Very-low-frequency (VLF) radio observations in Antarctica and North America provide the first evidence that bursts of energetic electrons from the Earth's radiation belts commonly precipitate into geomagnetically conjugate ionospheric regions in response to lightning. The electrons, with energies ranging from tens of keV to over one MeV, appear to be scattered out of their otherwise stable trap in the Earth's magnetic field by magnetospheric interactions with a regularly observed class of transient, lightning-generated VLF radio waves known as ducted whistlers. The precipitating electrons ionize atmospheric molecules at altitudes between 40 and 90 km, creating transient enhancements of ionization levels in conjugate locations. These ionospheric disturbances can be detected by their characteristic perturbations, sometimes called "Trimpi events," of the amplitude and phase of VLF transmitter signals propagating subionospherically within 200-250 km of the disturbed areas. The first detailed, one-to-one comparison of such signal perturbations, monitored in conjugate regions, with the multipath structure, arrival azimuths, and predicted electron scattering of simultaneously observed ducted whistlers suggests that every ducted whistler precipitates bursts of radiation belt electrons. If so, the estimated rate at which ducted whistlers contribute to radiation belt losses is comparable to that predicted for plasmaspheric hiss, a different class of magnetospheric wave that is often considered to control the structure of the belts. Lightning could therefore play a significant role in the maintenance of radiation belt equilibrium.