Unusually low airglow intensities in the Southern Hemisphere midlatitude mesopause region

Abstract

During the first part of a new set of airglow observations in the OH (6–2) and the O2 (0–1) Atmospheric bands from El Leoncito, Argentina, that started in August 1997, periods of surprisingly low intensities stand out. For many nights, mean O2 intensities reach only 30%, or less, of what we have seen in previous campaigns, from 1984 to 1994, at the same site, or a similar latitude. Such an anomaly is also observed, to a lesser degree, in OH intensities. An instrumental artifact in the intensity results can be ruled out by using the signal from the stellar background for a “field calibration”. A relation to the strong ENSO event with its major climate impact in 1997/8, may, of course, be suspected, although a statistical inference would be weakened by the scarceness of historical precedents of a similar magnitude