Atmospheric gravity waves observed in Brazil on 14 October 2023

Abstract. This study investigates the characteristics and origins of atmospheric gravity waves (AGWs) observed over Brazil following the annular solar eclipse of 14 October 2023. Utilizing a network of all-sky imagers located at Santarém, São João do Cariri and Bom Jesus da Lapa. Some medium- and small-scale gravity waves were identified in the mesosphere and lower thermosphere (MLT) via airglow emissions. To determine the likely sources of these waves, a reverse ray-tracing method was employed, incorporating empirical wind (HWM14) and temperature (NRLMSISE-00) models, alongside top cloud temperature data to account for tropospheric convection. Analysis of four distinct wave cases revealed a complex spectrum of propagation dynamics. At São João do Cariri, both a medium-scale wave (horizontal wavelength, λ_H = 174.4 km) and a small-scale wave (λ_H = 21.3 km) were traced back to stratospheric altitudes where their trajectories intersected the Moon's shadow. The absence of local convective systems suggests these waves were likely triggered by eclipse-induced atmospheric cooling. At Santarém, a large-scale wave (λH = 1523.8 km) with a high phase speed (218 m/s) was found to originate near the eclipse path at the tropopause. Conversely, a wave observed at Bom Jesus da Lapa (λ_H = 635.5 km), while geographically near the eclipse path, showed temporal and spatial alignment with tropospheric convection rather than the elipse path. These findings highlight the dual role of solar eclipses and convective processes in generating AGWs and demonstrate the efficacy of ray-tracing in distinguishing between transient astronomical triggers and persistent meteorological sources.