We show that the sudden increase in the circularly polarized component of the decametric emission in the event of Nov. 2, 1988 can be reasonably understood if the source of the highly circularly polarized emission is situated in the instantaneous Io flux tube. This conclusion agrees quite well with the results of other papers. Indeed, Lecacheux et al. (1991) proposed that the discussed emission belongs to the great arc. Riddle (1983), who has investigated the great arcs, found evidence that the emission appearing as the great arc on the dynamic spectra is created in the instantaneous Io flux tube. Genova & Aubier (1985) studied the high frequency limit of DAM emission storms and confirmed his result. Moreover, they found that most of the DAM emission is emitted from active magnetic flux tubes which certainly do not coincide with the instantaneous Io flux tube. The active magnetic flux tubes have to be shifted from Io position in the equatorial plane, by at least of longitude. Our investigation shows also that the total emission of the burst with exception of the highly circularly polarized component is emitted outside of the IFT. However, from the considered polarization measurements we cannot define the positions of these active magnetic tubes (the shift from the Io position) because of the fact that in our model the emission polarization ellipticity depends mainly on the plasma density in the transitional region rather than on the angle between the direction of emission generation and the magnetic field lines in the source. But on the other hand, it is the weak dependence on the angle that allows us to understand the observed stability of the emission polarization ellipticity during almost the whole burst as a simple consequence of the magnetospheric plasma density stability outside the IFT.
© European Southern Observatory (ESO) 2000
Online publication: March 9, 2000