The arc is visible in the STEREO WAVES Behind spectrum. The Io-D and Io-C regions are the result of radiation from the Jovian southern hemisphere. Io-D radiation comes from the leading side of the radiation cones of cyclotron masers near the Jovian auroral regions. Io-C is radiated from the lagging side of the cones.
This page shows other examples of recent Io-D events recorded by SWAVES.
Above is an Io-D event on November 6 2009.