Rapid Conjugate Appearance of the Giant Ionospheric Lamb Wave Signatures in the Northern Hemisphere After Hunga‐Tonga Volcano Eruptions.

AUSTRALIA; JAPAN

The explosive eruption of the Hunga‐Tonga volcano in the southwest Pacific at 0415UT on 15 January 2022 triggered gigantic atmospheric disturbances with surface air pressure waves propagating around the globe in Lamb mode. In space, concentric traveling ionosphere disturbances (CTIDs) are also observed as a manifestation of air pressure waves in New Zealand ∼0500UT and Australia ∼0630UT. As soon as the air pressure waves reached central Australia ∼0800UT, conjugate CTIDs appeared almost simultaneously in the northern hemispheres through interhemispheric coupling, much earlier than the arrival of the surface air pressure waves to Japan after 1100UT. Combining observations over Australia and Japan between 0800 and 1000UT, both direct and conjugate CTIDs show similar horizontal phase velocities of 320–390 m/s, matching with the dispersion relation of Lamb mode. The arrival of atmospheric Lamb wave to Japan later created in situ CTIDs showing the same Lamb mode characteristics as the earlier conjugate CTIDs. Plain Language Summary: The Hunga‐Tonga volcano eruption on 15 January 2022 has created the impulsive Lamb wave propagation on the surface air pressure that has been observed globally. The Lamb wave, typically moving near the ground at the sound speed of ∼340 m/s, traveled 6 hr to reach Japan. However, the Lamb wave signature in the Earth's ionosphere, the ionized component of the atmosphere, arrived 3‐hr earlier than expected, thanks to the property of the ionospheric plasma being controlled by the Earth's magnetic field. As soon as the surface Lamb wave reached Australia, the ionosphere above showed concentric wave shape of the traveling ionospheric disturbances (CTIDs), and the effect was mapped to Japan in the northern hemisphere along the conductive magnetic field lines. The much faster appearance of the ionosphere disturbances to the northern hemisphere through the magnetic field lines is beyond expectations. This is the first time such concentric waves from a volcanic eruption have been observed simultaneously in both hemispheres. Monitoring the ionospheric disturbances could be a robust early warning tool for diagnosing such explosive events on the planet Earth. Key Points: Concentric traveling ionospheric disturbances (CTIDs) driven by volcano excited Lamb wave are observed simultaneously in Australia and JapanDue to magnetic conjugate effect, the northern hemisphere CTIDs appear 3‐hr prior to the arrival of the surface Lamb waveBoth direct and conjugate CTIDs match with the theoretical dispersion relation of the atmospheric Lamb and gravity modes [ABSTRACT FROM AUTHOR]

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