Solar activity signatures in mesopause region temperatures and atomic oxygen related airglow brightness at El Leoncito, Argentina

Rotational temperatures and airglow brightness variations of the OH(6-2) and O2(0-1) bands measured at El Leoncito (32∘S,69∘W) from 1998 to 2002 are analysed to detect solar activity signatures. The emissions correspond to nominal altitudes of 87 and 95 km, respectively. The homogeneous and consistent data set covers the rise, the two distinct maxima, and the start of the decline of the present solar activity cycle. The modulation of solar activity around the Gnevyshev gap (particularly pronounced in this cycle) has been so strong as to motivate the expectation to detect its signature in such a relatively short data set. While at 87 km, we practically observe no correlation with solar radio flux, or at most a weak correlation in temperature, we find a moderate positive temperature and airglow brightness effect at 95 km. This is a remarkable difference, in view of the small separation between the two altitude levels. The quantitative results lie close to the lower limits of our previous estimates in a recent trend analysis. However, the behaviour at 95 km changes abruptly between anticorrelation, correlation, and no correlation. From December 1998 to July 2001 the correlation was very strong. From the standpoint of atmospheric nonlinear dynamics, variations in the degree of correlation in different years and at different observing sites should not be surprising.