Observation of Thermospheric Gravity Waves in the Southern Hemisphere With GOLD

The middle thermosphere from similar to 150 to 250 km is characterized by rapid increase in temperature with altitude and rapid ionization. The entire thermosphere is believed to be home to atmospheric waves that propagate through it, originating both in the atmospheric layers below and in the thermosphere itself. Within the middle thermosphere, direct observations of such waves are extremely sparse. The Global-scale Observations of the Limb and Disk (GOLD) far-ultraviolet imaging spectrometer is able to observe the middle thermosphere from geostationary orbit. During October 2018, a special observational campaign was performed, designed to identify atmospheric waves. Signatures in the 135.6-nm O airglow were seen that move northward with time, away from the southern polar region. These are consistent with a large-scale atmospheric gravity wave. These results are the first time 135.6-nm airglow has been used to track such a wave and highlight the ability of GOLD to observe such waves, even when at a modest amplitude, and track their motion. Plain Language Summary The upper region of the Earth's atmosphere, stretching from around 90-500 km above the surface, is known as the thermosphere. In this region, the temperature generally increases with altitude, but the strongest increase is in a region known as the middle thermosphere. The main source of heating in this region is absorption of ultraviolet light from the Sun, which also produces charged particles in this region, known as the ionosphere. Oscillations are observed in almost all the properties of the atmosphere at these altitudes, which are believed to result from waves within the atmosphere. In the middle thermosphere, there are very few direct observations of such waves. Global-scale Observations of the Limb and Disk (GOLD) is a new instrument that can observe the middle thermosphere by measuring emissions from the atmosphere call airglow. During a day in October 2018, GOLD observed what appear to be fluctuations in this airglow associated with such waves. The properties are determined, both from the GOLD observations and a theoretical model.