Satellite control of Jovian 2–6 MHz radio emission using Voyager data

Abstract

[1] Jupiter's satellite Io no longer has the only known effect in controlling the lowfrequency Jovian radio emissions. Menietti et al. (1998Menietti et al. ( , 2001) used a long and contiguous set of data in the range of 2.0-5.6 MHz from the Galileo spacecraft and found correlations with the orbital phase of Ganymede and Callisto. Recently, Higgins et al. (2006) used all of the Galileo orbiter data and found that Europa's phase shows a minor but statistically significant effect on the lower range of decametric emissions. In this paper, results are found that confirm previous work for all four Galilean satellites by combining Voyager 1 and Voyager 2 flyby data in the frequency range of 2.1-5.8 MHz. The data were analyzed using the unique occurrence probability data compilation technique that includes 10-hour averaging and satellite bias removal. A statistical significance Z-test was computed to compare sample populations for each enhanced region of occurrence against the background. We find significance values greater than the 95% confidence level (Z > 2s) for Io, Europa, Ganymede, and Callisto. Least squares fits to histograms of relative occurrence probability also show similar results. The cause of these correlations is believed to be Alfvénic interactions between the individual satellite and Jupiter.

Comparison between Cassini and Voyager observations of Jupiter's decametric and hectometric radio emissions

“…It is important to note that this technique is a powerful tool for analysis since it removes any local time effects and long‐term changes in data reception, and minimizes the quasi‐random background fluctuation affected by the interference of the spacecraft itself. This technique has already been performed by Higgins et al [2006], Higgins [2007], and Imai et al [2008].…”

“…To investigate the dependence of the System III longitude for non‐Io‐DAM components, we removed the data having an Io phase between 85° and 100° and between 235° and 260°, for each frequency [ Higgins et al , 2006; Higgins , 2007; Imai et al , 2008]. Figures 3c and 3d show the non‐Io‐related occurrence probability histograms of Cassini and of combined Voyager 1 and 2 data from 2 to 16 MHz in 2 MHz intervals in System III CML, respectively.…”

Angular beaming model of Jupiter's decametric radio emissions based on Cassini RPWS data analysis

“…The compiled data are best displayed as probability of occurrence graphs sorted by Jovian CML and Io phase. This relative occurrence probability is a calculated value between 0 and 1 for each longitude and Io phase bin as the total number of activity counts above the rotation threshold intensity divided by the total number of observation counts for each bin [ Higgins et al , 2006; Higgins , 2007]. An activity count occurs when the radio emission intensity is above the rotation‐based threshold for that particular frequency at that particular CML and Io phase value.…”

Radio emission from satellite-Jupiter interactions (especially Ganymede)

“…Figure 5a displays the occurrence probability of the part of these emissions originating from the northern hemisphere (i. A strong sinusoidal modulation is visible, not inconsistent with but much more prominent than that found by Higgins [2007]. Peaks at > 3σ level are visible on top of the sinusoidal modulation, at Φ Eu ∼ 50…”

“…Cyr, 1985]. More recent searches based on Voyager [Higgins, 2007], Galileo [Menietti et al, of the existence of satellite-induced radio emissions, convincing in the case of Ganymede and more marginal for Europa and Callisto. The signature of Ganymede's influence was found in Galileo PWS data recorded over 2 years in the range 3.2 to 5.6 MHz.…”