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This study presents the observation and evaluation of a meteotsunami in the Indian Ocean triggered by the Hunga‐Tonga volcanic eruption. The event was detected through tide gauges and bottom‐pressure recordings across the Indian Ocean, with an amplitude of 10–15 cm, lasting for a few days. A numerical model was used to understand the ocean's response to meteotsunami and evaluate the dynamics behind it. The model results show that the sea‐level oscillations result from the ocean waves generated by a propagating Lamb wave. In addition to interaction with bathymetry, refracted and reflected waves also determine the sea‐level variability. Our analysis shows that bathymetric slope plays a vital role in near‐shore processes. The spectral and spatial characteristics of the meteotsunami were reminiscent of seismic tsunamis. Our research on this rare event elucidates the unresolved issues and eventually leads to designing a blueprint for future observation and modeling of meteotsunamis and seismic tsunamis. Plain Language Summary: This study evaluates the observation of a rare meteotsunami event that occurred in the Indian Ocean. An atmospheric pressure wave generated by the eruption of the Hunga‐Tonga volcano in the Pacific Ocean caused the meteotsunami. The signatures of this event were captured by tide gauges installed along the coast and pressure recorders moored at the ocean floor. We demonstrate using a numerical model that fast‐moving atmospheric pressure waves, Lamb waves, caused the sea‐level oscillations. Interactions with bathymetry further influenced sea‐level variability in the basin, reflected waves, and refracted waves. The vulnerable areas showed a striking resemblance to the area impacted by the tsunami that hit the Indian Ocean in 2004. This research eventually helps to identify and incorporate observational and modeling issues associated with seismic tsunamis and meteotsunami. Key Points: We present the first comprehensive evaluation of meteotsunami in the Indian Ocean using observation and modelingA forced wave to free wave transformation happens on the continental slope, and the bathymetry slope is crucial to near‐shore processesThe meteotsunami exhibits a spectral and spatial similarity to seismic tsunamis that previously occurred in the Indian Ocean [ABSTRACT FROM AUTHOR]

We investigate the oceanic and ionospheric response in New Caledonia‐New Zealand and Chile‐Argentina to the 15 January 2022 Hunga‐Tonga volcanic eruption. For the first time, we highlight a reversed response in the oceans and in the ionosphere in terms of the amplitudes. The sea‐surface fluctuations due to the passage of the atmospheric Lamb wave (i.e., air‐sea wave) were not remarkable while the related ionospheric perturbation was considerable. Reversely, the eruption‐induced tsunami ("regular" tsunami) caused major variations in sea‐surface heights (∼1 m near the volcano and ∼2 m along the Chilean coastline), whereas the associated ionospheric perturbation was quite small. The observed large‐amplitude ionospheric response due to Lamb waves propagation is difficult to explain, and the coupling between the Lamb wave and the ionosphere is not well‐understood yet. For the first time, we estimate the delay between the Lamb waves and their signatures in the ionosphere to be ∼12–20 min. Plain Language Summary: The eruption of Hunga‐Tonga volcano produced a variety of atmospheric and tsunami waves recorded all over the world. We study the impacts of the eruption together on the oceans and in the ionosphere in New Caledonia‐New Zealand (near the volcano) and Chile‐Argentina (far from the volcano). At the sea surface, we observe two phenomena causing sea‐height variations. The first is a small tsunami (air‐sea wave) created by the Lamb wave: the high‐pressure atmospheric wave triggered by the eruption. The second is the tsunami induced by the eruption itself. Spectacularly, at 300 km altitude, in the ionosphere, we observe perturbations in the electron content caused by the Lamb wave and by the regular tsunami. We are the first to report on the reversed amplitude of the two phenomena in the oceans and in the ionosphere. The sea‐surface perturbation caused by the Lamb wave was not significant, while ionospheric perturbation was considerable. In contrast, the regular tsunami wave produced major variations. For the first time, we estimate the time delay between the Lamb wave and its signature in the ionosphere. Key Points: Joint study of oceanic and ionospheric response in New Caledonia‐New Zealand and Chile‐Argentina to the 15 January 2022 volcanic eruptionNear‐surface propagating Lamb wave caused a small tsunami in the ocean (air‐sea wave) and unusually strong disturbances in the ionosphereInversely, the eruption‐generated tsunami showed significant wave heights in the ocean and much smaller response in the ionosphere [ABSTRACT FROM AUTHOR]

The target scattering characteristics in microwave band are necessary to be researched for Orbital‐Angular‐Momentum (OAM) wave‐based radar applications. A theoretical description of electromagnetic (EM) scattering from a typical target by OAM waves is proposed in this paper. First, OAM waves are decomposed into plane waves in the spectral domain with different elevation and azimuth angles. Then, the scattering form of each decomposed plane wave is determined through coordinate system transformation and physical optics approximation. Formulas and numerical results are presented for OAM‐based radar scattering cross section of a perfect electric conductor and dielectric plate and a cylinder. Unlike the conventional results of EM plane wave scattering, the scattering properties of OAM waves from plate and cylinder are analysed with particular emphasis on OAM mode influence. The results provide insights into OAM wave‐matter interactions and may find important applications in wave propagation and OAM wave‐based radar detection and imaging. [ABSTRACT FROM AUTHOR]

The 2022 volcanic eruption in Tonga caused an unusually large tsunami around the Pacific. It travels with a faster apparent velocity and has larger amplitudes at long distances than what would be expected from a conventional tsunami from the volcanic source. This tsunami was generated by the moving atmospheric Lamb wave and traveled at the speed of the Lamb wave (0.31 km/s). Japanese data showed the amplitude of this first tsunami becomes small when approaching the coast, due to the weaker air‐sea coupling at the shallow depth. This wave split when passing the continental slope, and traveled at the speed of the ocean gravity wave. Therefore, the tsunami observed at the coast is delayed by thousands of seconds from the passage of the Lamb wave. Tsunamis generated by this atmospheric mechanism have not been previously observed by modern digital recording systems and should be considered in the tsunami warning systems. Plain Language Summary: A tsunami is usually generated by the sudden changes of the water heights, and caused by offshore earthquakes, coastal landslides, and submarine volcanic eruptions. The generated vertical displacement of the water propagates as a very long wave, and the tsunami waves become compressed with increased heights as they approach the coast. The 2022 volcanic eruption in Tonga caused an unusually large tsunami, which cannot be explained by conventional sources. The speed and amplitude are very different from theoretical values: the speed is about 0.31 km/s, whereas the average tsunami speed in the Pacific is 0.2 km/s. These data suggest that the tsunami from the Tonga eruption was excited by a pulse of atmospheric pressure as it traveled from the volcano. This source of the tsunami in the atmosphere needs to be considered for the tsunami warning system in the future. Key Points: Lamb wave produced by the volcanic eruption excites the sea surface as it travels across the Pacific and generates a tsunami pulseThe effect of the air‐sea coupling becomes weaker as the Lamb wave approaches the coastThe tsunami wave splits when passing the continental slope of Japan causing more complex waves [ABSTRACT FROM AUTHOR]

On 15 January 2022, around 4:30 UTC the eruption of the Hunga‐Tonga volcano, in the South Pacific Ocean, generated a violent underwater explosion. In addition to tsunami waves that affected the Pacific coasts, the eruption created atmospheric pressure disturbances that spread out in the form of Lamb waves. The associated atmospheric pressure oscillations were detected in high‐frequency in‐situ observations all over the globe. Here we take advantage of the similarities in the propagation and characteristics between atmospheric Lamb waves and long ocean waves and we use a 2DH ocean numerical model to simulate the phenomenon. We compare the outputs of the numerical simulation with in‐situ atmospheric pressure records and with remote satellite observations. The signal in the model matches the observed atmospheric pressure perturbations and reveals an excellent agreement in the wave arrival time between model and observations at hundreds of locations at different distances from the origin. Plain Language Summary: The underwater explosion of the Hunga‐Tonga volcano in the South Pacific Ocean generated atmospheric pressure disturbances, known as Lamb waves, that propagated and surrounded the globe several times. In this study, we exploit the similarities between atmospheric Lamb waves and long waves in the ocean (e.g., tsunamis) to simulate their propagation using an ocean numerical model. The comparison of our results with remote satellite data and in‐situ atmospheric pressure records reveals that our model correctly reproduces the propagation of the atmospheric disturbances generated by the volcano explosion. Key Points: The underwater Hunga‐Tonga volcano exploded generating Lamb waves that traveled around the Earth several timesWe simulate these waves using a hydrostatic shallow water equation oceanic modelThe results closely follow the observations of atmospheric pressure perturbations [ABSTRACT FROM AUTHOR]