Night-time measurements of the hydroxyl Meinel (3, 1) rotational band were used to infer the mesospheric temperature over Scandinavia from June through August, 1992. The resulting temperature time series showed spectrally-distinct, statistically-significant fluctuations with periods between 2 and 16 days, although only the 16-day oscillation will be discussed here. The period, amplitude and temporal history of this wave agree with model predictions and radar wind measurements of the (1, 3) Rossby normal mode, and are therefore consistent with its identification as the temperature signature of this mode. The relationship of these summer temperature oscillations and the occurrence of noctilucent clouds is discussed.