The connection between meteor showers and VLF atmospheric noise signals

There have been two different interests in the past as related to meteors and very low frequency (VLF) radiation in the atmosphere. The first deals with VLF pulses being produced by meteors entering the atmosphere, while the other deals with changes in the properties of the ionosphere due to meteors. To revisit these ideas, continuous measurements of VLF electromagnetic waves were performed simultaneously with optical imaging of meteors. The measurements were obtained during the Perseids, Orionids, and Leonids meteor showers during August, October, and November, 2007 and 2009. While unique VLF pulses could not be objectively associated with incoming meteors, the results indicate a distinct change in the background VLF atmospheric noise levels recorded on the nights of the meteor showers. We observed enhancements in the atmospheric noise parameter Vd, which is a useful quantitative measure of the impulsiveness of the noise, and is defined as the ratio (in decibels) of the root-mean-square amplitude to the average amplitude of the noise envelop, ranging from 2-2.5 dB (20-25% increase) relative to the normal levels. This enhancement in Vd is associated with decreased reception of VLF sferics at our station. These changes can be explained by either the attachment of ambient free electrons to the dust particles of meteoric origin, and/or the deposition of heavy ions with low mobility in the lower ionosphere. These ionospheric modifications cause more absorption, or inferior reflection conditions, for the background VLF noise sources, primarily produced by lightning.