An unusual airglow year at El Leoncito - evidence of chemical change?

J. SCHEER; E.R. REISIN

Mysore

Congreso; 39th COSPAR Scientific Asembly 2012; 2012

COSPAR

We report on a strange case of interannual variation from our lower midlatitude site El Leoncito (31.8ºS, 69.3ºW), Argentina. Brightness of the OH(6-2) band has been systematically higher than in almost all previous years, by about 30%. This situation lasted from mid February to mid December 2011, but has afterwards returned to normal (there was an earlier spell after mid-2010). Simultaneously, the intensity of the O2b(0-1) band has remained normal, except from September to mid December 2011, when there was a gradual rise, with peak deviation from normal behaviour, in November. On the other hand, rotational temperatures derived from both bands were close to the 1998-2001 climatological means reported earlier (Reisin Scheer 2009), on average over the strong day-to-day variability. The different behaviour of OH airglow brightness and the corresponding rotational temperature is not consistent with dynamical causes, since (even steady) vertical advection would affect intensity and temperature in the same sense. Also, the differences in the behaviour of both airglow emissions make changes in atomic oxygen unlikely to be responsible for the high OH brightness. We consider the possibility of changes in hydrogen chemistry to be involved, which calls for a better understanding of the atomic hydrogen mixing ratio and its variations in the mesopause region.