CENTRALE LYON - Post-doc "the horizontal propagation of atmospheric Lamb waves over planetary surfaces

ECL and Laboratory presentation

Founded in 1857, École Centrale de Lyon is one of the top 10 engineering schools in France. It trains more than 3,000 students of 50 different nationalities on its campuses in Écully and Saint-Étienne (ENISE, in-house school): general engineers, specialized engineers, masters and doctoral students. With the Groupe des Écoles Centrale, it has three international locations. The training provided benefits from the excellence of the research carried out in the 6 CNRS-accredited laboratories on its campuses, the 2 international laboratories, the 6 international research networks and the 10 joint laboratories with companies. Its excellent research and high-level teaching have enabled it to establish double degree agreements with prestigious universities and advanced partnerships with numerous companies. With its focus on sobriety, energy, the environment and decarbonization, Centrale Lyon intends to respond to the problems faced by socio-economic players in the major transitions.

Postdoc description

The Hunga Tonga–Hunga Ha’apai eruption of January 2022 stands as one of the most powerful volcanic events in recent history, producing a towering vertical plume that rose over 50 km above Earth’s surface. This extraordinary eruption generated a cascade of mechanical waves across all major geophysical domains: seismic waves through Earth’s interior, tsunamis across the oceans, and both acoustic and gravity waves throughout the atmosphere.

Among the atmospheric disturbances, the Lamb wave was particularly noteworthy (see Figure 1). Lamb waves are low-frequency, compressional waves that travel horizontally along a planetary surface. The wave generated by the Tonga eruption propagated at speeds close to the speed of sound (∼ 300m.s −1), persisted for several days, and was detected multiple times as it circled the globe. Remarkably, it was observed across a wide range of atmospheric layers, from the troposphere up to the ionosphere-thermosphere system. Over 800 barometric and seismic stations recorded pressure anomalies at the surface, while higher-altitude signatures were captured by GOES satellites, GPS Total Electron Content (TEC) data from more than 3000 receivers, airglow imaging, and Fabry–Perot interferometry. Additionally, recent studies have shown that the passage of these atmospheric disturbances over the solid Earth may have contributed to the excitation of the planet’s normal modes - a rare and compelling coupling between atmospheric and solid Earth dynamics.

The present postdoctoral project aims to investigate the horizontal propagation of atmospheric Lamb waves over planetary surfaces. Existing mathematical models describe their behavior in idealized scenarios, such as windless, isothermal atmospheres over flat surfaces, but do not account for important physical factors, including spatial and temporal variations in atmospheric properties, wave dispersion, nonlinearity, and planetary sphericity. To address these limitations, a two-dimensional mathematical model will be developed from the fundamental equations of fluid mechanics, incorporating the effects of atmospheric variability (fluctuations in the background speed of sound and wind) and surface curvature. A numerical solver will then be developed to resolve the governing equations and simulate Lamb wave propagation in realistic atmospheres, where both the speed of sound and horizontal winds vary in space and time. The solver will be used to study the Lamb wave generated by the Hunga Tonga–Hunga Ha’apai eruption, and the simulation outputs will be compared with ground-based measurements collected from around the globe.

• Matoza et al., Science, 377(6601), 2022

• Wright et al., Nature, 609, 2022

• Sepulveda et al., GRL, 50(19), 2023

• Inchin et al., AGU Advances, 4(6), 2023