Unusual Intensity Patterns of OH(6,2) and O(¹S) Airglow Driven by Long-Period Waves Observed Over the Andes Lidar Observatory

Simultaneous OH(6,2) and O(¹S) nightglow measurements obtained at the Andes Lidar Observatory (ALO) (30.3°S, 70.7°W) from September 2011 to April 2018 have been analyzed to investigate an unusual intensity pattern, that is, O(¹S) nightglow intensity enhancement concurrent with OH(6,2) nightglow intensity weakening. We identified 142 nights showing that behavior during the ∼6.5-year period. The data set comprised of these 142 nights displayed a semiannual occurrence rate with maxima during the equinoxes. A semidiurnal tide fitting applied to the 30-min bin size monthly averaged data shows that the largest amplitudes of the tide occur in April–May and August–September in both OH(6,2) and O(¹S). SABER atomic oxygen (O) climatology near ALO shows higher O densities near the equinoxes, with maximum O densities in March and September at ∼96 km. Lidar temperature analysis suggests that the O(¹S) enhancement concurrent with the OH(6,2) weakening is often accompanied by a temperature increase at 96 km and a decrease at 87 km. Simulations using airglow models have also been carried out to investigate the effect of a long-period oscillation on the OH(6,2) and O(¹S) airglow intensities. A sensitivity study has also been conducted to illustrate the effect of the characteristics of a long-period wave on the airglow intensity patterns.