Abstract Details
| Name: Hajime Kita Affiliation: Tohoku Univ. Conference ID: ASI2015_533 Title : Study on short-term variation mechanism of the Jovian radiation belt based on radio interferometer observations Authors and Co-Authors : Hiroaki Misawa (1), Anil Bhardwaj (2), Fuminori Tsuchiya (1), Chihiro Tao (3), Yoshizumi Miyoshi (4), Go Murakami (5), Takeshi Sakanoi (1), Yasumasa Kasaba (1), Akira Morioka (1), (1) Tohoku Univ., Japan, (2) Space Physics Laboratory, Vikram Sarabhai Space Centre, India, (3) IRAP, France, (4) Nagoya Univ., Japan, (5) ISAS/JAXA, Japan Abstract Type : Oral Abstract Category : Sun and the Solar System Abstract : Jovian synchrotron radiation (JSR) is the emission from relativistic electrons in the strong magnetic field of the inner magnetosphere, and it is the most effective probe for remote sensing of Jovian radiation belt from the Earth. Although JSR has been thought to be stable for a long time, recent intensive observations of JSR have revealed its short term variations with the time scale of days to weeks. Brice and McDonough [1973] proposed a scenario for the short term variations (hereafter the B-M scenario); i.e, the solar UV/EUV heating of Jovian upper atmosphere drives neutral wind perturbations and the increase in induced dynamo electric field leads to enhancement of radial diffusion. Previous studies confirmed that the short term variations in total flux density correspond to the solar UV/EUV variations. In addition, recent radio interferometer observations found short term variations in brightness distribution. However, confirmation of this scenario succeeded partially, and investigation of short term variations in brightness distribution and the possible causes needs to be investigated further. The purpose of this study is to confirm the B-M scenario based on observations of JSR and Jovian upper atmosphere. We made simultaneous observations of Giant Metrewave Radio Telescope (GMRT) and NASAs InfraRed Telescope Facility (IRTF) in 2011. From GMRT observations, the total flux density increased from 6th Nov. to 13th Nov in 2011, by about 5%, corresponding to the solar UV/EUV variations. From IRTF observations, intensity of H3+ also increased and estimated temperature variation was ~10K. On the other hand, peak position of JSR shifted outwards, which is inconsistent with enhancement of radial diffusion and implies unidentified strong local loss process. We examined this scenario by a radial diffusion model and found that enhancement of radial diffusion and Coulomb scattering could explain outward shift of JSR peak position. The GMRT observation also indicated short term variations in dawn-dusk brightness asymmetry of JSR. As a possible candidate, an effect of the dawn-dusk electric field in the Jovian magnetosphere was examined. We made simultaneous observation of the GMRT and SPRINT-A in 2014, where SPRINT-A is Japanese space telescope satellite launched in 2013 mainly dedicated for planetary science. We used dawn-dusk EUV emission ratio of Io plasma torus as an index of dawn-dusk electric field. We found that variations of dawn-dusk ratio of JSR correspond to the dusk-dawn ratio of Io plasma torus. The variations of dawn-dusk ratio of JSR are ~0.04, which corresponded to the electric field variations of 4 mV/m. Hence, dawn-dusk electric field is expected to affect the radiation belt electrons. |