Gravity wave activity in the middle atmosphere from SATI airglow observations at northern mid-latitude: Seasonal variation and comparison with tidal and planetary wave-like activity

The study investigates the gravity waves activity detected in the mesosphere/lower thermosphere (MLT) region (80-120 km) using airglow observations performed by the Spectral Airglow Temperature Imager (SATI) at the Sierra Nevada Observatory (SNO) (37.06 degrees N, 3.38 degrees W). In this analysis column emission rates of the OH Meinel (6-2) and O-2 Atmospheric (0-1) bands, as well as rotational temperatures derived from these emission rates are employed for the period of 1998-2015. The long time series allows the determination of gravity waves climatology at this site. The gravity wave activity content exhibits an annual variability with a maximum during winter and a faint increase in summer. It was found that gravity waves with periods of less than 3h are more prevalent than those with periods of 3-6h throughout the year, for both column emission rates and rotational temperatures. The gravity wave activity with periods of less than 3h is larger in summer, while gravity waves with period from 3 to 6 h have maximum activity around autumn-winter. The analysis showed that the gravity waves activity surpassed that of the semidiurnal tides, although was still smaller than the planetary wave activity, especially in summer when the planetary waves appear to dominate the dynamics of the MLT region. In general, wave activity is the main source of variability in both OH and O-2 airglow emissions with the planetary wave activity being the main driver of the O-2 emission variability. However, the rotational temperatures are more affected by seasonal variations, especially the OH rotational temperatures, accounting for more than the 40% of the overall observed variability.