On the relationship between whistlers, chorus, hiss, saucers, broadband electrostatic noise and the resonance cone

Waves named whistlers, chorus, hiss, saucers and low hybrid waves are often detected in space plasmas. These emissions are observed between the lower hybrid frequency and the electron gyrofrequency, but are given different names due to properties such as coherence, time duration and polarization. The waves are often classified as either electrostatic or electromagnetic, and are somtimes said to propagate on the resonance cone of the whistler mode. With the aid of dispersion surfaces, plots of frequency versus wavevector components, it can be shown that all these waves often correspond to one wave mode (one single surface). Sometimes the emissions called broadband electrostatic noise also propagate in this mode. Since electromagnetic theory for all angles of propagation relative to the ambient magnetic field is used, the smooth transition between so called eletrostatic and so called electromagnetic waves can be described in terms of a gradual change of the wavevector. To give an example of an instability over a wide range of wavevectors, a beam of auroral (keV) electrons is introduced. The highest temporal and spatial growth rates rates caused by such a beam can occur at the plasma frequency. However, a dispersion surface may be used to give some simple arguments showing that in an inhomogeneous plasma, the strongest emissions may occur below the plasma frequency. Furthermore, the significance of the resonance cone is discussed. (Author)