The cancellation factor (CF) is a model for the ratio between gravity wave perturbations in the airglow intensity to those in the ambient temperature and is necessary to estimate the momentum and energy flux and flux divergence of gravity waves in the airglow emissions. This study tests the CF model using T/W Na Lidar data and zenith nightglow observations of the OH and O(1S) emissions. The dataset analyzed was obtained during the campaigns carried out in 2015, 2016, and 2017 at the Andes Lidar Observatory (ALO) in Chile. We have used an empirical method to fit the analytical function that describes the CF for vertically propagating waves and compared the quantities through the ratio of airglow wave amplitude registered as a dominant event in the images to the wave amplitude in the lidar temperature. We show that the analytical relationship underestimates the observational results. We obtained good agreement with respect to the theoretical value for the O(1S) emission line. In contrast, the observational CF ratio deviates by a factor of ~2 from the analytical value for the OH emission.

This paper presents the results of a campaign covering a week of observations around the July 2, 2019, total Chilean eclipse. The eclipse occurred between 1922–2146 UTC, with complete sun disc obscuration happening at 2038–2040 UTC (1638–1640 LT) over the Andes Lidar Observatory (ALO) at (30.3$^\circ$S,70.7$^\circ$W). Observations were carried out using ALO instrumentation to observe eclipse–induced effects on the mesosphere and lower thermosphere region (MLT) (75–105 km altitude). Several mesosphere-sounding sensors were utilized to collect data before, during, and after the eclipse, including a narrow‐band resonance‐fluorescence 3D winds/temperature Na lidar with daytime observing capability, a meteor radar observing horizontal winds continuously, a multi-color nightglow all-sky camera monitoring the OH(6,2), O$_2$(0,1), O($^1S$), and O($^1D$) emissions, and a mesosphere temperature mapper (MTM) observing the OH(6–2) brightness and rotational temperature. We have also utilized TIMED/SABER temperatures and ionosonde measurements taken at the University of La Serena’s Juan Soldado Observatory. We discuss the effects of the eclipse in the MLT, which can shed light on a sparse set of measurements during this type of event. Our results point out several effects of eclipse–induced changes in the atmosphere below and above but not directly within the MLT. These effects include an unusual fast, bow–shaped gravity wave structure in airglow images, MTM brightness as well as in lidar temperature, strong zonal wind shears above 100 km, the occurrence of a sporadic E layer around 100 km, and finally variations in lidar temperature and density and the presence of a descending sporadic sodium layer near 98 km.

A new multi-static meteor radar (CONDOR) has recently been installed in northern Chile. This CONDOR meteor radar (30.3°S, 70.7°W) and the Adelaide meteor radar (35°S, 138°E) have provided longitudinally spaced observations of the mean winds, tides and planetary waves of the PW-tides interaction cases we present here. We have observed a Quasi-6-Day Wave (Q6DW) enhancement in MLT winds at the middle latitudes (30.3°S, 35°S) during the unusual minor South Hemisphere SSW 2019 by the ground-based meteor radars. Tidal analysis also indicates modulation of the Q6DW w/ amplitude ~15 [m/s] and diurnal tides w/ amplitude ~60 [m/s]. Another case we present here is a dominant Quasi-2-Day Wave (Q2DW) with up to 50 [km/s] amplitude occurring in SH summer 2020 and its interaction with the diurnal and semidiurnal tides. The period of this Q2DW activity changes from ~50hr to ~48hr since Jan 19, which suggests the phase locking mechanism [McCormack et al., 2010]. The 24hr-feature and 12hr-feature show off-phase variations during the Q2DW enhancement time with amplitude of ~40 [m/s].