Remote sensing by VLF using “Absolute OmniPAL”. 1. Investigation of the decay of sprite plasma

We consider observations by Dowden et al. (1997) of very strong early/fast Trimpis or VLF sprites observed at Darwin, Australia, only 2,000 km from the US Navy transmitter, NWC (21°48´S, 114°9´E). The unperturbed signal strength was about 20 mV/m during the Trimpi observations (at night). The echo amplitudes of the strong Trimpis ranged up to 8 mV/m, some 30 dB stronger than those studied previously in Colorado. The much higher signal/noise ratio enabled accurate measurements of the time variation of the amplitude and phase of the echoes