A document by Sukanta Sau. Click on the document to view its contents.

On July 2, 2019, a full solar eclipse has occurred in the location of the Andes Lidar Observatory in Chile. We have recorded data utilizing the set of sensors operating at the facility, such as daytime/nighttime lidar measurements of mesosphere temperature, Na density, and winds, nightglow images of the OH(6,2), O2(0,1), O(1S), and O(1D) emissions, GPS receivers, and the new meteor radar deployed at ALO on June 2019. The data show clear effects of the solar eclipse in the mesosphere region such as deep changes in temperature and density, as well as generation of unusual gravity wave structures. In this presentation, we want to discuss the image data showing the gravity wave activity during the evening following the eclipse event and discuss the generation mechanisms of the unusual gravity wave structures in the light of data recorded by all other instruments.

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 reports our simulations of the volume emission rate (VER) of the O($^1D$) redline nightglow perturbed by waves traveling across the thermosphere at around 250 km altitude. Waves perturb the electronic and neutral background densities and temperatures in the region and modify the O($^1D$) layer intensity as it is captured by ground-based nightglow instruments. The changes in the integrated volume emission rate are calculated for various vertical wavelengths of the perturbations. We demonstrate that, as the solar activity intensifies, the vertical scales of most likely observable TID waves become larger. For high solar activity, we demonstrate that only waves presenting vertical wavelengths larger than 360 km are likely to be observed. The variation of the range of likely observable vertical wavelengths with the solar cycle offers a plausible explanation for the low occurrence rate of TID in measurements of the redline nightglow during high solar activity periods. We have compared our results with those of \citeA{Negale:2018} and \citeA{Paulino:2018} to verify that observed vertical wavelengths distribute around 140-210 km, in good correspondence with our predicted threshold wavelength $\lambda_{z}^t\sim$160 km for very low solar cycle period.