Parametric mechanism for the formation of Jovian millisecond radio bursts
We develop a theory of formation of a fine structure in the dynamic spectra of the Jovian decametric radio emission. Main attention is paid to the formation of narrowband (NB) emission and quasiperiodic trains of short (S) bursts. Our model is based on the effects of occurrence of the amplitude‐frequency modulation and extension of the frequency spectrum of a signal during propagation of radiation in a medium with timevaried parameters. It is shown that nonstationary disturbances of the planetary magnetic field and strong frequency dispersion of the plasma at frequencies close to the cutoff frequency of the extraordinary wave in the Jovian ionosphere play a crucial role in the formation of NB emission and quasiperiodic trains of S bursts. As a result of the numerical experiments, it was concluded that the amplitude‐frequency characteristics of an initially continuous signal can drastically vary as a functions of the form of the magnetic field disturbance in the Jovian ionosphere. Structures similar to those observed in the real experiments, ranging from NB emission and quasiperiodic trains of S bursts to more complex structures, arise in the dynamic spectrum. Time variation in the conditions of generation and propagation of decametric radiation in the Jovian ionosphere is reflected in the dynamic spectrum as a time variation in the fine structure of the radiation. For example, a structure of the NB emission type is replaced by a quasiperiodic train of S bursts and vice versa.