PERIODIC AND QUASI-PERIODIC VLF EMISSIONS

A review of periodic and quasiperiodic VLF emissions observed at ground-based stations and in the Earth's magnetosphere is presented. Emissions with periods below 10 s are divided into three main groups: periodic emissions, hisslers and pulsing hiss, while the quasiperiodic emissions with periods above 10 s are divided into two main groups: QP1, which are definitely related to geomagnetic pulsations, and QP2, which are not obviously related to them, based on ground observations. However, it is pointed out that all types of quasiperiodic emissions with periods over 10 s observed onboard satellites show some association with geomagnetic pulsations which suggests that both QP1 and QP2 can have similar mechanisms for their generation. Different approaches to the theoretical modelling of periodic and quasiperiodic emissions are discussed.