Io Atmosphere - Plasma Torus Interaction.
U.Dudina, M.E. Brown. Geological and Planetary Sciences,
Caltech, Pasadena, CA 91125, USA

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 SystemIII density and temperature variations,
density variations at a period of 10.214 hours (termed System IV),
and periodic changes in location of the torus. 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.