Zebra-like fine spectral structures in Jovian decametric radio emission

Abstract : We report the first systematic analysis of zebra-like fine spectral structures in the decametric frequency range of Jovian radio emission (DAM). These zebra patterns are observed in the frequency range from 12 to 30 MHz as a quasi-harmonically related bands (from 3 to 9) of enhanced brightness. The features have been observed by the ground-based radio telescope URAN-2 (Poltava, Ukraine). In total, 55 zebra pattern events have been detected during the period from September 2012 to March 2016. The minimum duration of one single zebra pattern was 20 s, and the maximum one was 4 min 50 s. The intensity of the zebra stripes is 1-2 magnitudes lower than the intensity of Io-controlled DAM. The numbers of stripes in one event may vary in time. The frequency interval between neighboring stripes is from 0.26 to 1.5 MHz. The zebra patterns are strongly polarized and have been observed as right-handed and left-handed polarized radio emission. The zebra patterns are mainly detected in two active sectors of Jovian CMLs: 100 deg to 160 deg for northern sources (right-handed polarized) and between 275 deg and 60 deg (via 360 deg) for the southern sources (left-handed). No correlation with the position of Io has been detected. We conclude that the observed zebra patterns are a new type of narrow band spectral structures in the Jovian decametric radio emission.