@article{oai:nagoya.repo.nii.ac.jp:00020325, author = {YOSHIDA, Toshio and OHTSU, Jinsuke and HAYAKAWA, Masashi}, journal = {Proceedings of the Research Institute of Atmospherics, Nagoya University}, month = {Mar}, note = {The purpose of the present paper is to discuss the conditions of triggering VLF emissions by a natural whistler with variable frequency. The interaction time is defined by using the variation of unperturbed phase angle, which is determined by the spatial inhomogeneity of the medium and the wave frequency variation. Sample calculations of the interaction time are made for frequencies below the nose frequency on L = 4. A comparison of the interaction time with the bunching time has shown that VLF emissions are possibly triggered even by a weak whistler around 3 kHz in a very restricted range of geomagnetic latitude far from the equator in the upstream side of the electron. The study of the phase variations including the finite wave amplitude based on the complete equations of motion has confirmed that the condition that the interaction time exceeds the bunching time would be a threshold for phase bunching of electrons by a whistler, and hence triggering VLF emissions.}, pages = {31--48}, title = {ON THE CONDITIONS OF TRIGGERING VLF EMISSIONS BY A NATURAL WHISTLER}, volume = {27}, year = {1980} }