We show that the mesospheric Hydroxide (OH) and Water (H2O) correlate well with the solar irradiance. The OH variation correlates positively and the H2O variation correlates negatively with solar irradiance. Both species demonstrate a pronounced 27-day periodicity, which resembles the solar rotational cycle (Fig. 1). The 27-day harmonic in OH and H2O power spectra is strong during the period of high solar activity and negligible for the solar minimum conditions (Fig.2.) This proves that the 27-day variability in the OH and H2O data is caused by the solar rotational cycle.Figure. 2 The normalized power spectra of the tropical mean unfiltered daytime OH (top panel) and H2O (bottom panel).