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Astron. Astrophys. 355, 804-808 (2000)

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2. The event of November 2, 1988

The Io-A event was observed on Nov. 2, 1988 for approximately 3 hours at the Nançay (France) observatory. The observation results were published in the paper of Lecacheux et al. (1991). During the event, the central meridian longitude (CML) ranged from [FORMULA] to [FORMULA], and the Io phase ([FORMULA]) ranged from [FORMULA] to [FORMULA]. Fig. 1 (Fig. 4a in Lecacheux et al. 1991) shows the dynamic spectrum of the flux density of the event.

[FIGURE] Fig. 1. Dynamic spectrum of the flux density of the Io-A emission of 1988 Nov. 2. The great arc is indicated by the arrow

The spectral feature discussed in the present article extends from the highest frequency of the burst (more than 35 MHz) to approximately 27 MHz at the dynamic spectrum. At a fixed frequency the spectral feature is about 5 minutes long. The emission in the spectral feature and the emission which precedes it immediately have an essentially higher degree of the circular polarization than any other part of the storm. Lecacheux et al. (1991) found that the average degrees of the circular and linear polarization of the emission in the feature were [FORMULA] and [FORMULA], respectively, while in the remaining part of the burst they were [FORMULA] and [FORMULA]. Along the spectral feature the ellipticity of the polarization varies weakly with frequency. This is usual for the polarization observations of the Jovian decametric radio emission (Lecacheux et al. 1991; Dulk et al. 1992; 1994). Lecacheux et al. (1991) assume that this spectral feature is a great arc. This type of fine structure was noted for the first time on the Jovian emission dynamic spectra of Boischot et al. (1981).

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© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000