Auroral and low latitude VLF hiss

Abstract

The morphological features of VLF hiss observed at the auroral and low latitude stations are summarized and generation mechanisms are discussed. The suggestion that these waves are generated by Cerenkov mechanism is re-examined by computing incoherent Cerenkov radiated power from the soft and energetic electrons present in the inner magnetosphere, which falls short of the measured power spectral density. To explain the difference between the measured and computed spectral density it is suggested that the generation mechanism of VLF hiss is a two-step process. In the first step, waves are generated by incoherent Cerenkov process from the soft electrons present in the magnetosphere and as a second step, these small amplitude waves are amplified during interaction with energetic electrons having anisotropic

velocity distribution function. It is shown that the low latitude hiss consists of midlatitude hiss and equatorial hiss. Alternative generation mechanism for the equatorial hiss in terms of lightning discharges has also been discussed.