Scattering pattern of lightning‐induced ionospheric disturbances associated with early/fast VLF events

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Abstract
Simultaneous observations of early/fast Very Low Frequency (VLF) events at nine closely spaced (∼65 km) sites are used together with a numerical model of the propagation and scattering of VLF signals in the earth‐ionosphere waveguide to directly measure the scattering pattern of associated ionospheric disturbances. In cases when the causative lightning is within 700 km of the north‐south array of observing sites, early/fast VLF events are typically observed at no more than 2 or 3 sites, which indicates a narrow beam of the scattered signal in the forward direction. In the different cases studied, forward scattering patterns exhibit 15 dB beamwidths of less than 30° consistent with horizontal extent of 90±30 km.