[1] In this paper, we attempt to clarify the relationship between Jovian hectometric (HOM) and non-Io-related decametric (non-Io-DAM) radio structure. For that purpose, we extend the analysis by including more data and investigating statistical properties of the Jovian DAM and HOM radio emissions based on Cassini and Voyager observations, especially below 16 MHz. We have investigated these emissions observed by the Cassini, Voyager 1, and Voyager 2 spacecraft for specific Jovigraphic latitudes in the range of À3.7°-7.3°a nd local times in the range of 0.76-21.4 hours. We show a statistical comparison of Cassini, Voyager 1, and Voyager 2 data for occurrence probability in Central Meridian Longitude (CML) versus Io phase and in CML versus Frequency. The main results are as follows: (1) the detailed frequency structures of non-Io-related components can be seen for different spacecraft's local time and Jovigraphic latitude, (2) the high frequency of HOM extends up to near 10 MHz, and (3) a new DAM component, named the non-Io-D, appears from 40°to 60°CML in the frequency range of 7-11 MHz. On the basis of additional information of different behaviors of non-Io-B and non-Io-A structures in longitude depending on pre-and post-encounter of Cassini data, we improved the DAM angular beaming model that shows the cone half-angle of the emitting cone decreases as a function of frequency. We conclude that the changing beaming angle is not affected by Jovigraphic latitude of the spacecraft, but rather due to different local time of the source regions.

[1] The total flux density of Jupiter's synchrotron radiation (JSR) at 325 MHz was observed in 2007 with the Iitate Planetary Radio Telescope to investigate short-term variations in Jupiter's radiation belt with a time scale of a few days to a month. The total flux density showed a series of short-term increases and subsequent decreases. The variations in JSR and the Mg II solar UV/EUV index showed positive correlations, but the variations in JSR were preceded by those of the Mg II index by 3-5 days. The positive correlation supports a theoretical prediction that an enhancement in the radial diffusion driven by thermospheric winds in the upper atmosphere causes changes in relativistic electron distributions in both the radiation belt and the total flux density of JSR. The radial diffusion model was used to examine the hypothesis that temporal changes in the radial diffusion rate could be an origin of the short-term variation. The model includes physical processes such as radial diffusion, energy degradation by the synchrotron radiation, and several loss processes. We applied a radial diffusion coefficient of 3 × 10 −8 L 3 /s and found a suitable solution that accounted for both the time scale of the short-term variations and the 4 day time lag. The model also showed that strong electron loss processes other than the synchrotron radiation are needed to explain the electron distribution in low L regions. An empirical electron distribution model showed that the synchrotron radiation does not act as a loss of electrons in such areas.Citation: Tsuchiya, F., H. Misawa, K. Imai, and A. Morioka (2011), Short-term changes in Jupiter's synchrotron radiation at 325 MHz: Enhanced radial diffusion in Jupiter's radiation belt driven by solar UV/EUV heating,

No abstract

Abstract.The modulation lanes in Jupiter's decametric radio spectra were discovered by Riihimaa [1968]. We have developed a model for the mechanism responsible for their production in which the free parameters have been adjusted to provide a very close fit with the observations. In our model,