Temperature anisotropy and beam type whistler instabilities

Whistler instabilities have been investigated for two different types, i.e., a temperature anisotropy type instability and a beam type instability. A comparison between the two types of whistler instabilities is made within the framework of linear theory. A transition from one type to the other is also discussed, which is an extension of the work on electrostatic beam and Landau instabilities performed by O’Neil and Malmberg for electromagnetic whistler instabilities. It is clarified that the essential source of the whistler instability is not a beam kinetic energy, but a temperature anisotropy even for the beam type whistler instability.