Triggered emissions observed at Varanasi (India)

Abstract

Whistler triggered emissions recorded at a low latitude station e.g. Varanasi are described. The study covers various aspects of these emissions including riser, riser followed by constant frequency emissions, hiss and oscillating tones. Analysis shows that the whistlers have propagated along paths with L-values lying between L=1.9 and 2.4, suggesting that these whistlers are to be regarded as mid-latitude whistlers. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal mode. The measured intensity of the triggered emissions is either equal to or more than that of the source wave and also varies from one event to another. It is proposed that these emissions are generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra.