The dynamic vertical coupling in the middle and lower thermosphere (MLT) is documented over the Maïdo observatory at La Réunion island (21°S, 55°E). The investigation uses data obtained in the framework of the Atmospheric dynamics Research InfraStructure in Europe (ARISE) project. In particular, Rayleigh lidar and nightglow measurements combined with other observations and modeling provide information on a mesospheric inversion layer (MIL) and the related gravity waves (GWs) on 9 and 10 October 2017. A Rossby wave breaking (RWB) produced instabilities in the sheared background wind and a strong tropospheric activity of GWs on 9–11 October above La Réunion. The MIL was observed on the night of 9 October when a large amount of tropospheric GWs propagated upward into the middle atmosphere and disappeared on 11 October when the stratospheric zonal wind filtering became a significant blocking. Among other results, dominant mesospheric GW modes with vertical wavelengths of about 4–6 km and 10–13 km can be traced down to the troposphere and up to the mesopause. Dominant GWs with a wavelength of ~2–3 km and 6 km also propagated upward and eastward from the tropospheric source into the stratosphere on 9–11 October. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature and OH profiles indicate that GW activity in the middle atmosphere affects the upper atmosphere with waves breaking at heights below the MIL and in the mesopause. Several techniques are illustrated on nightglow images to access GW activity and spectral characteristics at the mesopause for high and low frequency GWs on the nights of 9–10 October. In conclusion, intense tropospheric activity of GWs induced by RWB events can be linked with MILs at the subtropical barrier in the South-West Indian Ocean during austral winter.

A mesospheric model of the airglow emission is developed to recover the night variations observed at ground level. The model is based on a 1D vertical photochemical model, including the photodissociation and heating processes. The spectral radiation is calculated at high altitude and propagated through the atmosphere to the ground. We also include short scale vertical dynamic such as turbulences and the molecular diffusion. Simulations reveal realistic emissions when compared with space observations. In addition, we estimate the impact of changes associated with parameterized atmospheric tides. The comparison with observations is performed over high altitude and ground level. We confront the model outputs at high altitude with satellite observations (SABER and GOMOS) and the simulations propagated at ground level are compared to local measurements campaigns performed in France and India. Biases between observed and simulated radiances and volume emission rates are suspected to be due to the impact of gravity waves or the large scale dynamic.

The impact of a mesospheric temperature inversion on the vertical propagation of gravity waves has been investigated using OH airglow images and ground-based Rayleigh lidar measurements carried out in December 2017 at the Haute-Provence Observatory (OHP, France, 44N). These measurements provide complementary information that allows the vertical propagation of gravity waves to be followed. An intense mesospheric inversion layer (MIL) observed near 60 km of altitude with the lidar disappeared in the middle of the night, offering a unique opportunity to evaluate its impact on gravity wave (GW) propagation observed above the inversion with airglow cameras. With these two instruments, a wave with a 150 min period was observed and was also identified in meteorological analyses. The gravity waves’ potential energy vertical profile clearly shows the GW energy lost below the inversion altitude and a large increase of gravity wave energy above the inversion in OH airglow images with waves exhibiting higher frequency. MILs are known to cause instabilities at its top part, and this is probably the reason for the enhanced gravity waves observed above.

11 A mesospheric model of the airglow emission is developed to recover the night variations observed 12 at ground level. The model is based on a 1D vertical photochemical model, including the photodis-13 sociation and heating processes. The spectral radiation is calculated at high altitude and propa-14 gated through the atmosphere to the ground. We also include short scale vertical dynamic such 15 as turbulences and the molecular diffusion. Simulations reveal realistic emissions when compared 16 with space observations. In addition, we estimate the impact of changes associated with parame-17 terized atmospheric tides. The comparison with observations is performed over high altitude and 18 ground level. We confront the model outputs at high altitude with satellite observations (SABER 19 and GOMOS) and the simulations propagated at ground level are compared to local measurements 20 campaigns performed in France and India. Biases between observed and simulated radiances and 21 volume emission rates are suspected to be due to the impact of gravity waves or the large scale 22 dynamic. 23

Airglow layers provide an excellent tracer for observing upper-atmosphere dynamics, such as gravity waves. Conversely, seismic activity generates atmospheric waves that grow in amplitude as they propagate upward, producing measurable perturbations at ionospheric heights. While the theoretical observation of earthquake signatures in the atmosphere has been discussed in several studies, no investigation has yet quantified the real detection threshold of airglow cameras. Here, we present a complete methodology to achieve the first detection of seismic waves in the OH airglow layer at 87 km, from instrument description to analysis techniques. To demonstrate the effectiveness of our approach, we model the airglow signature of a typical Mw8 event and apply the proposed techniques to the resulting synthetic data.