ANALYTICAL MODELS FOR THE RESPONSES OF THE MESOSPHERIC OH-ASTERISK AND NA LAYERS TO ATMOSPHERIC GRAVITY-WAVES

Analytic models are developed to describe gravity wave induced perturb ations in the high nu OH Meinel Band emissions and in atomic Na densi ty. The results are used to predict the fluctuations in OH intensity and rotational temperature, Na abundance, and the centroid heights of the OH and Na layers. The OH* model depends critically on the assumed form for the atomic oxygen profile. In this study the O profile is mo deled as a Chapman layer, which is in excellent agreement with MSIS-90 . We. also neglect the wave-induced redistribution of O-3 because the chemical lifetime of oz;one in the mesopause region is short compared to most gravity wave periods. Under these conditions the OH response is Delta V/V-u similar or equal to -3[1 - (z - Z(OH))/h(OH) + (z - z(O H))(2)/sigma(1)(2)] Delta rho/rho(u), where Delta V/V-u are the relati ve emission rate fluctuations, Delta rho/rho(u) are the relative atmos pheric density fluctuations, z(OH) similar or equal to 89 km is the la yer centroid height, h(OH) similar or equal to 3.6 km, and sigma(1) si milar or equal to 8.0 km. By using these results, we show that cancell ation of the induced perturbations in emission intensity and rotationa l temperature is significant for short vertical wavelengths. The ampli tude attenuation in both parameters is proportional to exp(-m(2) sigma (OH)(2)/2), where m = 2 pi/lambda(z) and sigma(OH) approximate to 4.4 km is the rms thickness of the OH layer. For example, at lambda(z) = 15 km, the predicted rotational temperature perturbation is only 20% o f the atmospheric temperature perturbation. Because the most sensitive instruments are only capable of accuracies approaching +/-2 K, there are few reported observations of waves with lambda(z) less than or equ al to 15 hm. The cancellation effects are not as limiting in OH intens ity observations because the relative intensity perturbations;are larg er than the relative temperature perturbations, and intensities can be measured more accurately than temperature, especially with broadband instruments. Fluctuations in the emission rate are largest on the bott omside of the OH layer, similar to 3.75 km below the layer peak (simi lar to 89 km), where the effects due to the redistribution of atomic o xygen dominate. Fluctuations in rotational temperature are largest nea r the peak of the OH layer, where the volume emission rate is largest. The similar to 3.75 km separation between the maxima of the intensity and rotational temperature perturbations is largely responsible for t he phase differences observed in the fluctuations of these parameters. Rotational temperature and Krassovsky's ratio are found to be very se nsitive to the form of the background temperature profile. Wave-induce d OH layer centroid height fluctuations coupled with the mean lapse r ate of the background temperature profile can contribute significantly to the observed rotational temperature fluctuations, especially for t he shorter wavelength waves lambda(z) less than or equal to 15 km. The OH intensity fluctuations are relatively insensitive to the temperat ure profile as well as variations in atomic oxygen density and therefo re appear to be excellent tracers of gravity wave dynamics. OH tempera ture observations are best suited for studying long-period waves, incl uding tides, with lambda(z) greater than or equal to 15 km.