Most prominent airglow night at El Leoncito

Abstract

In our data set of presently more than 750 nights of OH and O2 airglow observations at lower mid-latitudes, the night of April 25, 1999 stands out for several reasons: the greatest mean O2 intensity we have ever observed and by far the strongest quasi-monochromatic gravity wave signature in OH intensity (with period of about 38 min), accompanied by a prominent day-to-day variation in O2 intensity, and a strong tidal signature simultaneously present in intensities and temperatures at both emission heights. Whereas gravity wave events like this are relatively rare at our site, the slower variations are obviously regular features, similar to what we have seen on other occasions. The quantitative details of the observed phenomena are analyzed in order to establish possible relationships. We conclude from comparison with similar cases that high nocturnal means are frequently accompanied by strong gravity wave signatures, but not generally by strong tidal activity. Finally, di:erent potential mechanisms, including solitons, are briefly reviewed.