Location of lightning-induced electron precipitation from measurement of VLF phase and amplitude perturbations on spaced antennas and on two frequencies

The phase and amplitude perturbations on a VLF subionospheric transmission can always be expressed in terms of a perturbation or echo phasor. It is believed that lightning-induced electron precipitation (LEP) can produce a localized increase in ionization which acts as a scattering center and so echo source for subionospheric VLF waves. The phase of the echo relative to the direct signal will differ on spaced antennas if the angle of arrival of the two signals differ. Similarly, this realtive phase will vary with frequency if the group delay of the signals differ. Thus measurement of these differences allows location of the scattering centers and so the LEP. Locations made show a significant grouping in a region where both the lightning intensity is high and the field line passes through the center of the inner radiation belt