Optical and VLF Imaging of Lightning-Ionosphere Interactions

Abstract

electrodynamic coupling between the troposphere, mesosphere, lower ionosphere, and magnetosphere. Lightning-induced electron precipitation encompasses all of these regions, from atmospheric and mesospheric electrodynamics, to radiation belt scattering, to precipitation and disturbances of ionospheric communication channels. Furthermore, observation of direct lightningionospheric coupling mechanisms can lead to the understanding of ion chemical dynamics in the upper-mesosphere, and lower-ionosphere, including determination of ambient electron density profiles and unknown chemical interaction parameters. Sprites and their possible conjugate effects due to relativistic electrons also constitute a coupling between the regions, including lightning effects on the mesosphere and ionosphere. Geomagnetic disturbances highlight the coupling between these regions, with the resulting perturbations in the magnetosphere and ionosphere easily detectable. OBJECTIVESObjectives of the current three-year effort are to address the following scientific questions: What role do lightning generated whistlers play in the formation of the slot region of the radiation belts? How can VLF remote sensing be used to quantitatively measure the energy spectra and flux of precipitating electrons associated with LEP events? What is the contribution of MR whistlers and lightningtriggered-plasmaspheric hiss to the loss of electron radiation? How do sprites evolve on a fine spatial and temporal scale, and how does this evolution compare to conventional and streamer breakdown theory? What is the cause of the fine-scale bead-like features of sprites? How does the thundercloud activity relate to the spatial and temporal evolution of sprites? How are sprites and sprite halos related to conductivity perturbations on the ionosphere, observed as early/fast perturbations to VLF transmitter signals? What is the effect of in-cloud lightning on the lower ionosphere? How can VLF remote sensing be used to quantify atmospheric ion-chemistry interaction parameters? Are long-recovering Early VLF events the result of a different causative mechanism than their short-recovery counterparts, and are long recovery events more likely to be observed on all ocean-based paths than paths over land?If so, what is the physical source of this preference? APPROACHOur approach consists of the use of optical and wideband VLF/LF measurements to document high altitude optical phenomena and VLF/LF holographic imaging of ionospheric disturbances together with the causative lightning flashes. The VLF/LF antennas are deployed at seven high schools and 1