A review of observational, theoretical and numerical studies of VLF triggered emissions

We review theoretical and numerical studies of VLF triggered emissions generated by manmade signals propagating in the whistler mode in the magnetosphere. Instead of listing all the past studies on the subject we select some of those works which give important ideas and the theoretical basis for future studies. The main purpose of the paper is to clarify what problems remain unresolved and to make suggestions for future studies. We first describe the phenomenon of VLF triggered emissions and give a brief review of experiments and observations. We then summarize the basic physics of VLF wave-particle interactions, which is indispensable for an understanding of the triggering mechanisms. We review important ideas and theories, as well as numerical models so far employed, summarize the present understanding of the phenomenon and consider briefly those problems which need further study. Especially, we focus our attention on numerical simulations whose capabilities in nonlinear physics are increasing with the increasing power of supercomputers.