Further evidence of triggering chorus emissions from wavelets in the hiss band
Résumé
The results of detailed spectral analyses and direction finding for ELF data containing simultaneous hiss and chorus have been reported on the basis of the data observed on-board GEOS 1 satellite in the outer magnetosphere at a high geomagnetic latitude (Λ ∼- 25°). A combination of the present results with those from our previous equatorial studies has yielded the following findings : (1) each chorus element has a tendency to originate from the hiss band and is asymptotic to the hiss band ; (2) the intensity and occurrence of the chorus are closely correlated with the intensity of the underlying hiss ; (3) the hiss band exhibits structures or wavelets (i.e. monochromatic wave component with significant duration) and we notice the existence of the causative wavelet at the foot of each chorus element ; (4) when we expect triggering chorus from a wavelet near the upper edge of the hiss band, the duration of the wavelet increases with decreasing intensity ; (5) very similar φ (azimuthai angle) values are noticed for both the hiss and chorus, suggesting that both phenomena come from the same source region. These observational facts might lead us to conclude that a wavelet existing near the upper edge of the hiss band is able to generate a chorus emission through coherent wave-particle interaction in the outer magnetosphere, as in the case of active VLF wave injection experiments.