DUCTED WHISTLER-MODE SIGNALS RECEIVED AT 2 WIDELY SPACED LOCATIONS

Whistler-mode signals from a single VLF transmitter that have propagat ed in the same duct, have been observed simultaneously at Faraday, Ant arctica (65 degrees S, 64 degrees W) and Dunedin, New Zealand (46 degr ees S, 171 degrees E). The signals received have group-delay times tha t differ in the order of 10 ms, which can be explained by the differen ces in southern-hemisphere sub-ionospheric propagation time from duct exit region to receiver for the two sites. This difference has been us ed to determine the location of the duct exit region, with confirmatio n provided by arrival-bearing information from both sites. The whistle r-mode signals typically occur one or two days after geomagnetic activ ity, with K-p greater than or equal to 5. The sub-ionospheric-propagat ion model, LWPC, is used to estimate the whistler-mode power radiated from the duct exit region. These results are then combined with estima ted loss values for ionospheric and ducted transmission to investigate the role of wave-particle amplification or absorption. On at least ha lf of the events studied, plasmaspheric amplification of the signals a ppears to be needed to explain the observed whistler-mode signal stren gths.