  The dominant viewpoint on Jovian decametric S-burst emission neglects the
time delay of the radiation, although its base theory of electron cyclotron
maser instability allows a significant decreasing of X-mode group velocity near
the cutoff frequency at the bottom of source region. We searched for effects of
the frequency-related delay of radiation in broadband Jovian radio storms
consisting of periodic S-bursts (S-burst trains) at 16 to 30 MHz. It was found
that up to 1% of bursts in a train are of distorted meandering shape in dynamic
spectrum, where the emission from one radio source was observed at several
frequencies simultaneously. It is difficult to explain such spectra in terms of
radio waves beaming or causality without significant frequency-related delay of
radio emission. We found experimentally that the frequency drift rate of middle
lines of such events coincides with the drift rate of disturbances in common
S-bursts. This indicates a general distortion of the dynamic spectrum of
S-bursts. As a result, the correlation method for the measurement of the
spectral distortion is proposed. Using this method, we found the approximation
coefficients for the distortion in 32 spectra of 8 Io-B storms. The corrected
spectra formally show that S-burst trains do not move mainly outward from
Jupiter, as it is usually assumed, but fly in the opposite direction. Our
simulation confirms that the dispersion is capable in principle to reproduce
the found spectral distortion. Hence, the dispersion-like phenomena in Jovian
S-bursts deserve discussion because they have no satisfactory explanations in
terms of traditional approach.
