The Unusual Intensity Pattern of OH(6,2) and O(1S) Airglow Observed Over the Andes Lidar Observatory

Simultaneous observations of OH(6,2) and O(¹S) nightglow at the Andes Lidar Observatory (ALO) from September 2011 to April 2018 have been analyzed to investigate an unusual intensity pattern showing an O(¹S) nightglow intensity enhancement concurrent with an OH(6,2) nightglow intensity weakening. About 142 nights have been identified in the time period showing a remarkable biannual occurrence rate with maxima during the equinoxes. A semidiurnal (12-h) tide fitting applied to the 30-min bin size monthly averaged data shows that the largest amplitudes of the semidiurnal tide were observed for the months of April and August-October in the OH(6,2) data and April and September in the O(¹S) data. It was also found that SABER’s atomic oxygen at the O(¹S) peak height is 1.3-2.5 times higher during the nights that displayed the unusual intensity pattern. Simulations using the nonlinear, time-dependent, OH Chemistry Dynamics (OHCD) and Multiple Airglow Chemistry Dynamics (MACD) models have also been used to investigate the effect of a long-period wave on the OH(6,2) and O(¹S) airglow intensities. The simulation results are in good agreement with the observations and replicate the unusual intensity pattern observed in the OH(6,2) and O(¹S) airglow data.