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 having 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.