4.7 Observations of short term variation of Jovian synchrotron radiation

We have made detailed observations of Jovian decimetric radiation (DIM) from relativistic electrons in the Jovian radiation belt by using the Kashima 34 m antenna to seek the existence of DIM short-term variations. In these observations, the sky tipping method was used to correct the terrestrial atmospheric extinction effect. We also evaluated the background radio sources noise, which has caused serious problems in previous observations. As a result we showed for the first time that the Jovian synchrotron radiation has variations in intensity over a period of a few days. We then developed a model of Jovian synchrotron radiation based on the empirical models of Jovian magnetic field and the distribution of particles in the Jovian radiation belt derived from direct measurements made by past spacecraft. By comparing this model with the results of observations, we clarified that when the Jovian synchrotron radiation intensity is increasing, the spatial distribution of electrons in the Jovian radiation belt changes in such a way that the electrons concentrate at Jupiter's magnetic equatorial plane. Next, we developed and numerically tested a computer code relating to the transport of particles in the Jovian radiation belt. We showed that the observed flux increase of Jovian synchrotron radiation for a few days can be explained by a scenario in which the radial diffusion coefficient of electrons in the radiation belt increases. Furthermore, we performed a comparative analysis with the solar F10.7 observed on the earth during the same period, and we showed the possibility that this increase in the radial diffusion coefficient arises from heating of the Jovian ionosphere by solar UV/EUV radiation during the observation period.