tokens: would be one of the possible reasons for the difference between 2014 and 2016. Because the energetic electrons drift slower than the corotation and they spent more time in the inflow/outflow sectors, the drift orbit of higher-energy electron displaces more than that of the lower energy electron. However, statistical analysis indicated that the IPT and JSR did not have a strong positive correlation as expected from the hypothesis. Figure 3 indicates the scatter plot of the dusk-to-dawn ratio of JSR and IPT. Spearman’s rank correlation coefficient is −0.22 for 2014 and 0.048 for 2016. A correlation t-test at 10% significance level shows that JSR and IPT are regarded as having no correlation. The correlation between JSR and the solar wind dynamic pressure is not significant either. The energetic electrons drift slower than the corotation, which means that they may take longer to organize over all longitudes when a change in the dawn-dusk electric field occurs. The rotation period (corotation + magnetic gradient drift) of 10 MeV and 16 MeV electron are ∼10.5 hr and ∼11.0 hr at 1.5 Rj , respectively. In this study, response delays can be negligible comparing to the observation cadence. We do not consider any time lag between IPT and JSR, because the dawn-dusk electric field affects JSR and IPT at the same time. Hence, the short-term variation in the dawn-dusk asymmetry of JSR cannot be explained only by the dawn-dusk electric field. Figure 3. Scatter plot of the dusk-dawn ratio of IPT and JSR for 2014 and 2016. indicates Spearman’s correlation coefficient. Although these results did not support our hypothesis, we cannot rule out the possibility that the dawn-dusk electric field was masked by some other processes that could control the short-term variations in the dawn-to-dusk ratio of JSR. Here, we discuss the possible causalities of why the correlation is weak. Because the ionospheric potential difference induced by the field-aligned current depends on the ionospheric conductivities, the solar UV/EUV effect might appear in the dawn–dusk asymmetries of JSR. The stronger the solar UV/EUV, the weaker the dawn-dusk electric field because of higher conductivity. The third panel of Figure 2 indicates the solar UV/EUV. We cannot find a strong correlation between both dusk-to-dawn ratios and the solar UV/EUV; however, the conductivity variation should be taken into account. Because the ionospheric potential difference is the source of the electric field, the ionospheric potential map should also be taken into consideration. Dawn-dusk electric field is mapped from the ionospheric potential difference induced by the field-aligned current. As the potential difference becomes smaller at the lower latitude, the effect of the dawn-dusk electric field would be smaller in the innermost magnetosphere. The study with an ionospheric potential solver (e.g., Nakamizo et al. 2012 ) for Jovian ionosphere would give us a clue to estimate these effects quantitatively.
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