Na lidar and MF radar measurements of temperature and horizontal winds were conducted simultaneously during several continuous 24 h periods in March and April 1996 at the Urbana Atmospheric Observatory. The data are used to determine the amplitude and phase profiles of the 24 and 12 h tides in the mesopause region between about 82 and 100 km. The measured amplitudes and phases of the tidal components of the horizontal winds are generally consistent with the predictions of the global-scale wave model (GSWM). The measured 24 h temperature amplitude is comparable to the GSWM predictions between 85 and 96 km but is significantly larger than GSWM above 96 km. The measured phase progression is downward below 94 km with an inferred vertical wavelength of 14¿1 km. Above 94 km the temperature phase progression is upward with a vertical wavelength of 12¿1 km. The measurements suggest the presence of a diurnal heat source in the lower thermosphere which is generating a strong downwardly propagating 24 h wave.¿ 1997 American Geophysical Union