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During observations at conjugate stations Siple, Antarctica, Roberval, Canada VLF noise bursts were found to be associated on a one-to-one basis with amplitude perturbations of subionospheric radio propagation.
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This effect, first noted by Antarctic field operator, M. Trimpi in 1963 and called for that reason the 'Trimpi Effect', was reported by Helliwell et. al. [1973]