Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13d2111k&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM13D-2111
Astronomy and Astrophysics
Astronomy
[2774] Magnetospheric Physics / Radiation Belts, [6220] Planetary Sciences: Solar System Objects / Jupiter, [6939] Radio Science / Magnetospheric Physics, [6954] Radio Science / Radio Astronomy
Scientific paper
Jupiter's synchrotron radiation (JSR) is the emission from relativistic electrons in the strong magnetic field of the inner magnetosphere, and it is the most effective prove for remote sensing of Jupiter's radiation belt from the Earth. Although JSR has been thought to be stable for a long time, intensive observations for JSR have made after the collisions of comet P/SL9 to Jupiter in 1994, and these observations revealed short term variations of JSR on time scale of days to weeks. However, the mechanisms which cause the short term variations of total flux density and brightness distribution have not been revealed well. In order to reveal the mechanism of short term variations of JSR more precisely, we have made radio image analysis using the NRAO (National Radio Astronomy Observatory) archived data of the VLA [*]. Brice and McDonough [1973, Icarus] proposed a scenario for the short term variations: i.e, the solar UV/EUV heating for Jupiter's upper atmosphere drives neutral wind perturbations and then the induced dynamo electric field leads to enhancement of radial diffusion. It is also suggested that induced dynamo electric field produce dawn-dusk electric potential difference, which cause dawn-dusk asymmetry in electron spatial distribution and emission distribution. So far the following results have been indicated for the short term variations. Miyoshi et al. [1999, GRL] showed that a short term variation event at 2.3GHz is well correlate to solar UV/EUV flux variations. Tsuchiya et al. [2010, Adv. Geosci.] showed that JSR at 325MHz and 785MHz have short term variations. These JSR observations confirmed the existence of the short term variation which is caused by solar UV/EUV. However, the effect of solar UV/EUV heating on the spatial distribution of JSR has never been confirmed, so this study is the first attempt to confirm the solar UV/EUV effect on spatial distribution of JSR. We have selected the data observed from 28th Jan. to 5th Feb. 2000 at 327MHz. During the period, solar UV/EUV flux expected on Jupiter showed almost monotonic increase. It is expected from the analysis for the period that the enhancement of radial diffusion caused by solar UV/EUV heating produces total flux enhancement and dawn-dusk asymmetry of the emission distribution of the JSR. We can therefore examine the scenario by measuring total flux density and dawn-dusk peak emission ratio of JSR, and their relationships to the variation of solar UV/EUV activity. A preliminary result shows that total flux density variations occurred corresponding to the solar UV/EUV variations, but we couldn't find variations in the dawn-dusk asymmetry above the one rms level calculated from the background image. *The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Kita H.
Misawa Hiroaki
Morioka Akira
Tsuchiya Fuminori
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