VLF/LF Measurements of Ionospheric Effects Associated with Lightning, Whistlers and Energetic Electron Precipitation

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This grant will support an experimental investigation of transient and localized perturbations of the lower ionosphere that occur in association with atmospheric lightning discharges and with natural wave bursts that originate in the magnetosphere. Recent experimental evidence has demonstrated the importance of the lower ionosphere and the middle atmosphere in the coupling between parts of the atmosphere-ionosphere-magnetosphere system. Lightning-induced effects occurring in the troposphere are coupled to the ionosphere through the mesosphere, creating impulsive ionospheric electric fields, altering ionospheric electron density and conductivity, and launching electromagnetic whistler waves. Energetic radiation belt particles precipitated as a result of magnetospheric interactions whistler waves and with burst of VLF emissions are deposited into the lower ionosphere and the mesosphere, causing secondary ionization, x- rays, light emissions, and heating. The aim of this grant is to gain better understanding of the processed of downward and upward coupling in the magnetosphere-ionosphere-mesosphere-troposphere system and of the effects of these processes on the dynamics of the earth's radiation belts. The transient perturbation events are remotely sensed by means of high resolution measurements of the amplitude and phase of subionospheric VLF/LF radio signals, which are sensitive to perturbations of electron density at mesospheric and D-region altitudes. Simultaneous observations at selected locations in the United States and Canada will be used to investigate: (i) the geographic distribution and geomagnetic conjugate relationships of event occurrence and characteristics, (ii) the association of VLF signal perturbation events with lightning discharges, (iii) spatial structure of perturbed ionospheric region(s) associated with individual lightning flashes as well as with active thunderstorm centers, and (iv) the role of atmospheric discharges in the dynamics of the radiation belts.