Sporadic enhancements of 673.1 nm emissions from the Io plasma torus were found in ground-based observations in 1998 and 1999. Just after the onset of the enhancement on September 21, 1999, narrow-band kilometric (nKOM) radiation began to be observed by the Galileo/PWS in the Jovian magnetosphere. During this period, quasi-periodic burst groups (Morioka et al., 2006) were also observed by the PWS, and Jovian "auroral flare" (Waite et al., 2001) events were found on the same day by the Hubble Space Telescope. The sudden appearances of both nKOM radiation and auroral flare suggest the arrival of a remarkable solar-wind disturbance at the Jovian magnetosphere. In this paper, we present evidence that these enhancements are stochastic, related to solar wind disturbances.