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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 Hunga-Tonga volcanic eruption occurred on 15 January 2022 generated different modes of atmospheric and ionospheric waves. Using the Geostationary Operational Environment Satellite-17 (GOES-17), Aqua and Global Positioning System (GPS) satellite observations, an atmospheric and ionospheric multi-layer study of the Tonga volcano induced signatures over the New Zealand region is performed. The visible and infrared channel data of GOES-17 and Atmospheric Infrared Sounder (AIRS) data from NASA Aqua satellite confirm the presence of a highly convective zone and occurrence of concentric Lamb and gravity waves at lower atmospheric altitudes. The Total Electron Content (TEC) derived from 175 GPS stations covering the entire New Zealand region brings out two dominant modes of Travelling Ionospheric Disturbances (TIDs) having periodicity between 30 and 50 min. These two different modes having the phase speeds of 542 m/s and 354 m/s are allied to atmospheric gravity waves and Lamb wave triggered gravity waves respectively and are observed to propagate towards the south-west direction over the New Zealand region. [ABSTRACT FROM AUTHOR]