Radio science results: Observations of short term variation of Jovian synchrotron radiation

Abstract

Detailed observations of Jovian decimetric radiation (DIM) from relativistic electrons in the Jovian radiation belt ware made 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. The background radio sources noise, which has caused serious problems in previous observations was also evaluated. As a result it was shown for the first time that the Jovian synchrotron radiation has variations in intensity over a period of a few days. A model of Jovian synchrotron radiation was then developed 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, it was clarified that when the Jovian synchrotron radiation intensity was increasing, the spatial distribution of electrons in the Jovian radiation belt changed in such a way that the electrons concentrate at Jupiter's magnetic equatorial plane. Next, a computer code relating to the transport of particles in the Jovian radiation belt was developed and numerically tested. It was shown that the observed flux increase of Jovian synchrotron radiation for a few days could be explained by a scenario in which the radial diffusion coefficient of electrons in the radiation belt increased. Furthermore, a comparative analysis with the solar F10.7 observed on the earth during the same period was performed, the possibility was shown that this increase in the radial diffusion coefficient arose from heating of the Jovian ionosphere by solar UV/EUV radiation during the observation period.