We modify the Jovian ionosphere-magnetosphere coupling model presented by Hill (1979) to include rotational slippage of the neutral atmosphere at ionospheric heights, relative to a frame of reference corotating rigidly with Jupiter. In the modified model, as altitude increases, the drift velocities of neutrals and ions relative to the corotating frame increase from zero at the bottom of the ionosphere to their respective maximum values at the top, and the corotation lag of the magnetosphere is enhanced for a given rate of mass loading of the magnetosphere. The height variations of the drift velocities of neutrals and ions in the ionosphere and the enhancement factor for the corotation lag of the magnetosphere are related to the atmospheric eddy diffusion coefficient at ionospheric heights. On the basis of ionospheric properties deduced from measurements of Pioneer 11, Voyager 1, and Voyager 2, we derive height profiles of ion and neutral drift speed for various possible values of the eddy diffusion coefficient. If we accept the ion injection rate from Io (1029 ions/s) and the ion transport rate through the Jovian magnetosphere (3¿1028 ions/s), corresponding to the observed values of the corotation lag of the Io torus (Δ&ohgr;I=0.04&ohgr;J) and the critical distance for magnetospheric corotation (L0=20), respectively, the effective ionospheric conductance is reduced by a factor of the order of 10, resulting in an enhanced corotation lag, for a given rate of mass loading, by the same factor compared to earlier models. The eddy diffusion coefficient in the high-latitude ionosphere is inferred to be ~1013 nn-1/2m-1/2/s, or about a factor of 20 larger than the value inferred from Voyager measurements at near-equatorial latitudes. ¿ American Geophysical Union 1989