A series of studies were performed concerning the response of low-latitude ozone and temperature in the stratosphere and mesosphere to short-term solar ultraviolet variability associated with the rotation of the sun. Response times of temperature to solar UV variability in the stratosphere are found to be unexpectedly long (6 days at 2 mbar) and to become much shorter in the mesosphere (1 day at 0.01 mbar). Maximum sensitivity of temperature to solar variability (0.3 K/% 205-nm radiation) is found to occur near 70 km. The coupling of the temperature and ozone response to solar UV variability has been isolated by studying ozone responses with and without temperature effects. Temperature effects tend to increase rather than decrease the amplitude and to shift the response time of stratospheric ozone to solar variability to an earlier time. Higher in the mesosphere, where H2O mixing ratios should be much lower, ozone is found to increase with increasing solar UV. Observed responses of HNO3 and NO2 to solar UV variability are also briefly discussed. The theoretical response of middle atmosphere species and temperature to solar UV variability is discussed in detail in a companion paper (Brasseur et al., this issue).