Complex Ray Theory for Ion Cyclotron Whistlers

Abstract

SINCE their discovery on VLF recordings from the Injun 3 and Alouette satellites in 1964 (ref. 1), proton whistlers, and more recently helium whistlers² have proved to be useful diagnostic probes for studying the constitution of the topside ionosphere^3,4. An ion cyclotron whistler of either of these types is associated with a “fractional hop” whistler, and appears on the spectrogram as a trace breaking away from the “electron whistler” trace at a “crossover” frequency, and then approaching asymptotically the proton or helium gyrofrequency at the level of the observing satellite. The theory of these whistlers was given by Gurnett et al.⁵, who considered the effects of positive ions on electromagnetic waves in the topside ionosphere. As well as the usual electron whistler, polarized with a right handed sense in the northern hemisphere, it is possible at certain altitudes and for certain frequency ranges for the left hand polarized mode to propagate.