An investigation of the coupling between the ionosphere and the thermosphere is made using coordinated measurements obtained simultaneously with the Chatanika incoherent-scatter radar and two Fabry-Perot spectrometers at College, Alaska, during a 2 hr period in February 1982. One of the Fabry-Perot spectrometers measured the line shape of the oxygen 630.0-nm emission, and the other measured the line shape of the oxygen 557.7 nm emission. The measurements were used to obtain the neutral and ion velocities, the neutral, ion, and electron temperatures; and the electron densities in the E and F regions. Interpreting these measurements using the ion energy equation for the F region yields the height(s) at which heat exchange between the ions and neutrals balances the sum of frictional heating due to differences in the ion and neutral velocities and heat exchange between the electrons and ions. This height can be interpreted as the location of the oxygen 630.0-nm emission profile centroid, thus providing an estimate of the height of the neutral temperature measurements. Furthermore, the centroid location and extent in altitude depend on the processes producing O(1D) in aurorae. A unique balance height was not typically found, but balance often occurred over a wide range of altitudes, depending on the assumption of a pure O+ or a pure NO+ ionosphere, which is consistent with model calculations of the 630.0-nm emission rate profile. Though the coordinated optical-radar measurements available are limited, the initial results demonstrate that important questions relating to ion and neutral composition, chemistry, and dynamics can be examined by the methodology employed in this study. ¿ American Geophysical Union 1993