Case Studies on Mesospheric Fronts at Low Latitudes over Brazil

Abstract. This study investigates four mesospheric front events observed over Cachoeira Paulista (23° S, 45° W), Brazil, between 2007 and 2008, using coordinated measurements from an all-sky airglow imager, meteor wind radar, and sodium temperature lidar. The events, recorded on 14–15 September 2007, 5 October 2007, 31 March 2008, and 3 September 2008, were classified as mesospheric bores, two undular and two turbulent based on airglow morphology and atmospheric background structure. Vertical profiles of wind and temperature, along with vertical wavenumber diagnostics, revealed the presence of thermal and thermal-Doppler ducts supporting the bores. Classical complementary emission responses were observed in single-duct environments, while multi-duct layering led to complex airglow signatures, including mixed bright and dark fronts. This is the first study in Brazil’s low-latitude region to employ simultaneous multi-instrument observations for mesospheric bore analysis, offering new insights into duct dynamics, emission behavior, and wave–duct interactions in the mesosphere and lower thermosphere.