Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Volume 120, Issue 8, Pages 6614-6623Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015JA021374
Keywords
Jovian radiation belt; Jovian thermosphere; synchrotron radiation; H3+emission
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Funding
- NASA, Science Mission Directorate [NNX-08AE38A]
- Tohoku University Institute for International Advanced Research and Education
- Indian Space Research Organisation
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We report the first comprehensive observations of Jovian synchrotron radiation (JSR) and H-3(+) emission from the Jovian thermosphere to investigate the generation process of short-term (days to weeks) variations in the Jovian radiation belt. The observations were made by the Giant Metrewave Radio Telescope and NASA Infrared Telescope Facility during November 2011. The total flux density of JSR increased by approximately 5% between 6-9 November and 12-17 November, associated with the increased solar UV/EUV flux. From 7 to 14 November, a possible rise in the infrared H-3(+) emission was observed in the middle-latitude region, corresponding to a temperature variation of approximately 10K. These results are consistent with the scenario that the solar UV/EUV heating causes variations in the thermospheric temperature and JSR. Radio images along the equatorial region showed that the JSR intensity decreased inside 1.5 Jovian radii (R-J) and the peak position shifted outward. This implies that energetic electrons are attenuated by some internal loss process, despite the simultaneous increase in radial diffusion. A physical model for the radiation belt shows that such an internal loss process can explain the observed variation of brightness distribution. Typical loss time scale is longer than strong diffusion limit, which suggests the existence of some pitch angle diffusion process such as wave-particle interaction. Thus, variations of the total JSR flux density and thermospheric temperature seem consistent with the scenario, and the brightness distribution of JSR can be explained by the increase in radial diffusion accompanied by internal loss processes.
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