Polarization Characteristics of Io-Related Jovian Decametric Radiations

抄録

Polarization measurements of Io-related Jovian decametric radiations (DAM's) were made in a frequency range from 20.5 to 25.5 MHz at the Zao observatory of Tohoku University, Japan. In the analyses of axial ratios of polarization ellipses, the following two factors were particularly investigated which were expected to deform the original axial ratios of Io-related DAM's; i.e., i) interferences caused by reflected wave components from ground, and ii) mutual cross-talks between one free-space mode wave to another free-space mode wave in anisotropic magnetized plasma along the ray paths. Totally 20 Io-related radio storms and 2 non-Io-A radio storms were selected for the analyses. Our major results are as follows: i) Most of Io-related DAM events indicate highly right-handed (RH) elliptical polarization and the mean value of the axial ratios for RH events is -0.31 ± 0.09 (standard deviation). ii) Io-A and 10-13 related DAM events indicate the significant difference in their axial ratios; i.e., -0.35 ± 0.08 and -0.26 ± 0.06 for RH Io-A and RH Io-B related DAM events, respectively. iii) Io-related DAM events indicate slightly more linear polarization than non-Io-A DAM events.