Effects of atmospheric disturbances on polar mesopause airglow OH emissions

Abstract

Temporal variations in the absolute intensity ( I ) and the rotational temperature ( T ) of the polar winter airglow OH(8, 3) bands were observed over Longyearbyen, Spitsbergen (78.2°N), in December 1984. The high latitude of the observatory places it in a continuous polar night around the winter solstice period, thereby permitting 24‐hour optical measurements. Spectral analyses of the I and T time series reveal a dominant semidiurnal component and a wave with a period of 3.7 hours. Other waves with shorter periods may be present for part of the total observing period, but the signal‐to‐noise ratios of their amplitudes averaged over a 24‐hour interval are too low to permit definitive identification. The ratio η of the correlated Fourier components of ( I − Ī )/ Ī to that of (an overbar signifies time average) has amplitude 3.2 ± 0.9 and 4.3 ± 1.3 for the 12‐ and 3.7‐hour waves, respectively, while the phase ϕ of η for these periods is 6° ± 16° and −12° ± 12°. The value of η for the 3.7‐hour wave can be compared with the theoretical prediction of η for gravity wave modulation of the OH emission. For an emission height of 87 km and an atomic oxygen scale height ℋ(O) of −2 km, theory gives |η| = 4.2 and ϕ = 0° for the 3.7‐hour wave, in good agreement with the observation. The theoretical interpretation of η at the 12‐hour period is complicated by the likelihood that the observed semidiurnal oscillation is not a simple tide. For tidal modulation of the OH nightglow, theory gives |η| between 2.6 and 0.9 and ϕ between 0° and 10° for high‐order semidiurnal modes and for the same values of emission height and ℋ(O) as above.