Variation of OH(6-2) and O2 rotational temperature (nocturnal means) at El Leoncito (32°S, 69°W). The low values on January 8, 2001 are obviously part of day-to-day variations controlled by strong activity of the 2-day planetary wave that started in December, and lasted until late January. Note that the mean seasonal variation (blue line) only shows a shallow "New Year's low", that extends through January.

Compare the corresponding intensity plots.