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

摘要

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 oefficient 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.