VLF Holographic Imaging of Lightning-Induced Disturbances of the Lower Ionosphere

Stanford University, Stanford CA

Investigators

Abstract

9910532 Inan, Umran S. An experimental investigation is proposed of localized and transient disturbances of the lower ionosphere which occur in association with lightning discharges. The overall purpose of the proposed program is to understand the physical mechanisms of lightning-ionosphere interaction, which lead to rapid conductivity changes, and to determine the global effects of lightning-induced electron precipitation on the radiation belts. The disturbances are imaged remotely using the Holographic Array for Ionospheric Lightning (HAIL) which measures the amplitude and phase of very low frequency (VLF) signals propagating in the nearby Earth-ionosphere waveguide. The HAIL system was established under the predecessor grant to this proposal and has already led to the discovery of precipitation of radiation belt electrons by obliquely propagating (nonducted) whistler waves. It provides high-resolution measurement of localized disturbances, and thus enables the capture of a sufficient number of events needed to investigate several science questions. The ionospheric disturbances are believed to be produced by direct interaction of lightning radiation and quasi-static fields with the ionosphere or by bursts of energetic electrons precipitated out of the radiation belts by whistler waves originating in lightning discharges. Both of the phenomena are now known to regularly occur; however, assessment of their global significance requires that the spatial extent and distribution of events be determined. HAIL consists of VLF receiver systems deployed at nine high schools in Wyoming, Colorado, and New Mexico. The data from the HAIL sites is transmitted back to Stanford over the Internet, and is made available to the scientific community over the Internet within 12 hours of acquisition. The proposed program provides important educational outreach opportunities, the students and teachers from the HAIL schools and others are encouraged to work with the data and interact with the Stanford investigators.