The stability of the Io plasma torus-atmosphere interaction is examined. A simple plasma deflection model describes how transients in the plasma flux and the content of the atmosphere affect the ionospheric conductance, limiting the plasma bombardment and, hence, the supply of atmospheric species to the torus. The supply of the torus is seen to be determined by the thermal structure of the plasma, namely, the amount of low energy plasma producing atmospheric erosion vs. that which produces ionization, so that the torus supply rate is not simply proportional to the torus ion density. ¿ American Geophysical Union 1993