On the correlation of whistlers and associated subionospheric VLF/LF perturbations

Abstract

Several periods of whistler‐associated subionospheric signal perturbations (i.e., Trimpi events) observed at Palmer, Antarctica (L ∼2.4) have been studied. In a case study of the time signature of the signal perturbations during a 10‐min recording period on March 30, 1983, the time delay between the whistler‐producing spheric and the onset of the change was found to be in the range 0.52–0.62 s, independent of the amplitude of the change. Event amplitude, as expected from previous work, was found to be well correlated with the associated whistler wave intensity. Other temporal features such as the rise and decay times of the perturbations were also found to be independent of the event amplitude. These results are consistent with a recent theoretical model of gyroresonant particle scattering interaction in the magnetosphere. The amplitudes of simultaneous perturbations on signals of different frequency and arrival bearing were well correlated in several cases, but exhibited case to case differences that appear to depend upon the spatial distribution of precipitation regions. Whistler occurrence times during two recording periods were found to approximately obey a Poisson distribution, while the statistics of Trimpi event occurrence in those periods showed significant deviations from Poisson behavior. The probability of random alignment in time of the whistlers subionospheric and perturbations is estimated to be < 10−14, in agreement with previous inferences of a cause and effect relation between whistlers and VLF/LF perturbations. Although nearly all of the whistlers observed originated in northern hemisphere lightning, the first example was found of a Trimpi event associated with a southern hemisphere source.