Hydroxyl nightglow emissions arise from a region of the atmosphere several to 10 km thick centered at about the mesopause. The intensity of the nightglow ⟨I⟩ is therefore a superposition of contributions from individual thin emitting layers. The inferred rotational temperature ⟨TI⟩ is an intensity weighted average of the temperatures throughout the emitting region provided that the overall temperature variation of the region is small compared with the average temperature, and that the Boltzmann exponent in the rotational line intensity distribution is not much larger than unity. Acoustic-gravity waves propagating through the emitting region produce fluctuations in the OH nightglow; intensity and temperature oscillations, ⟨ΔI⟩ and ⟨ΔT⟩, are conveniently related by the ratio ⟨&eegr;⟩=(⟨ΔI⟩/⟨I¿⟩)/)⟨ΔTI⟩/⟨T¿I⟩), where the overbar refers to time-averaged quantities.

When the vertical wavelength &lgr;v of a disturbance is large compared to the vertical thickness of the emitting region, ⟨&eegr;⟩ is accurately given by &eegr;=(DI/I¿)/(ΔT/T¿) for a thin layer at the peak emission height. However, when &lgr;v is comparable to or smaller than the emission region thickness, ⟨&eegr;⟩ values can vary widely from the peak emission height ratio &eegr;. When &lgr;v is small, the magnitude of the normalized fluctuation in net intensity ‖ ⟨ΔI⟩/⟨I¿⟩ ‖ is considerably reduced from the large &lgr;v value due to cancellation effects of out-of-phase layers in the emitting region. Therefore, there is an observational bias toward detection of nightglow fluctuations from waves with &lgr;v greater than emission region thickness. Values of ⟨&eegr;⟩ versus period are reported for several horizontal wavelengths based on a dynamical-chemical model that accounts for realistic OH chemistry and the dynamics of acoustic-gravity waves propagating vertically through a height-dependent basic state atmosphere. ¿ American Geophysical Union 1988