Polar mesopause gravity wave activity in the sodium and hydroxyl night airglow

The OH (6–2) band and the Na D lines in the night airglow have been observed from Spitsbergen (78°N latitude) during a 3‐day period in the end of November 1983. Regular and quasi‐regular variations in temperature and the OH and sodium intensity were observed and are here interpreted in terms of gravity wave theory. In particular, waves with periods in the range 90–120 min having overlying ripple structure, with periods of 5–15 min, were observed. From the phase difference between the waves in the OH and sodium layer a height difference between the centroid of the two emissions of less than 1 km could be deduced. A gravity wave induced vertical eddy diffusion coefficient in the range 8 × 106 to 8 × 107 cm²/s was estimated from OH‐enhanced intensities. No significant net heating or cooling was observed during gravity wave activity. The gravity wave activity was not associated with geomagnetic activity. Mean OH (6–2) band and sodium night airglow intensities were 1.9 kR and 75 R, respectively.