Io Atmosphere - Plasma Torus Interaction.

U.A. Dudina, M.E. Brown (Caltech)

We use a long-term data set of simultaneous observations of the sodium in neutral cloud around Io and Io plasma torus to determine the response of Io's atmosphere to changes in the plasma torus.

The data consist of 6 months of almost-nightly observations of the sodium in the extended neutral clouds and ionized sulfur in plasma torus. The data set allows us to trace periodic changes in both Io neutral cloud and plasma torus. Periodic changes seen in the Io plasma torus are: Jupiter System III density and temperature variations, density variations at a period of 10.214 hours (termed System IV), and periodic changes in torus location. Variations in the Io plasma torus and changes in the Io orbital location cause changes in plasma bombardment rate at Io. These changes should cause observable variations in the neutral clouds.

We analyzed the time variations in neutral sodium clouds and their interaction with variable flux of torus plasma bombarding clouds and Io surface. We will discuss physical processes responsible for this type of interactions.