Unusually low airglow intensities in the Southern Hemisphere midlatitude mesopause region

During the first part of a new set of airglow observations in the OH (6-2) and the O-2 (0-1) Atmospheric bands from El Leoncito, Argentina, that start ed in August 1997, periods of surprisingly low intensities stand out. For m any nights, mean O-2 intensities reach only 30%, or less, of what we have s een in previous campaigns, from 1984 to 1994, at the same site, or a simila r latitude. Such an anomaly is also observed, to a lesser degree, in OH int ensities. An instrumental artifact in the intensity results can be ruled ou t 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 .