APERIODIC ION TEMPERATURE VARIATIONS IN THE IO PLASMA TORUS.

The paper considers the observed aperiodic variations of S III temperature reported by ground-based observers, which take place on time scales short in comparison with the radiation and electron collision relaxation times. It is suggested that ion-ion charge exchange processes are responsible for the heating, and ion-atom collisions are the source of the cooling. The fluctuations are attributed to random strong variations in the output of neutral matter from the volcanoes and surface of Io. Freshly ionized sulfur that will have near full corotation gyroenergy will undergo charge exchange with thermal doubly ionized sulfur and oxygen, thus producing hot S III. Newly injected neutral atoms can cool the ambient hot plasma by collisions on a time scale comparable to their lifetime against ionization processes.