On the origin of ''modulation lines'' in the dynamic spectrum of the Jovian decametric radiation

The origin of the fine structure of the Tovian decametric radiation ''modulation lines'', is considered. ''Modulation lines'' are the system of inclined bands of larger or smaller brightness in the dynamic spectrum. Two possible mechanisms of formation of ''modulation lines'' in the dynamic spectrum of the Jovian decametric radiation are discussed: 1) the Cotton-Mouton effect in the Jovian ionosphere and magnetosphere, 2) frequency modulation of intensity in the source. On the basis of both mechanisms, dynamic spectra are calculated, and characteristic features, distinguishing the spectra with the bands due to Cotton-Mouton effect from those formed by the second mechanism, are outlined. The conditions for the origin of the Cotton-Mouton effect in Jupiter and of the frequency-spectrum modulation in the source are discussed. To explain the ''modulation lines'' by the Cotton-Mouton effect in the Jovian ionosphere or lower magnetosphere, electron concentrations of 103-104 cm-3 are sufficient. The difficulties of explanation (similarly to the zebra structure in the solar radio emission) of the frequency-spectrum modulation in the source by intense excitation of plasma waves in the layers, where the condition of double plasma resonance on harmonics of the electron or ion gyrofrequency are satisfied, are indicated