Dispersion-like phenomena in Jovian decametric S-bursts: Tabooed Facts

TL;DR

This study reveals that dispersion effects significantly distort Jovian decametric S-burst spectra, challenging traditional interpretations of their source motion and suggesting the need to consider frequency-dependent delays in analysis.

Contribution

It introduces a new spectral distortion measurement method and demonstrates that dispersion effects can explain observed spectral anomalies in Jovian S-bursts.

Findings

Spectral distortions up to 1% observed in S-burst trains.

Corrected spectra suggest S-bursts may move toward Jupiter, not away.

Dispersion can reproduce the spectral distortions observed.

Abstract

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.