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The massive eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano in Tonga on 15 January 2022 at 04:15 UTC had a global impact and triggered an atmospheric wave and a tsunami. We first analyzed observation data from meteorological stations and tide gauges at 12 locations. Low-frequency trends in the observation data were removed by using a high-pass filter. Fourier and wavelet spectral analyses were applied to determine the frequency characteristics of the filtered data. Modal analysis was developed and used to investigate natural oscillation periods based on bathymetry. The results showed that the Lamb wave generated by the atmospheric pressure wave arrived ~ 7 and ~ 44 h after the eruption. The tsunami arrived ~ 11 and ~ 45 h after the eruption, which corresponded to the arrival time of the Lamb wave. The dominant periods of the Lamb waves were ~ 7.7 and ~ 7.5 min, and for the tsunamis they were ~ 9.9 and ~ 28.7 min. The periods derived from the spectral analysis matched the natural oscillation of the eigenperiod derived from the modal analysis, in eight out of the twelve stations. This study provides valuable insight and information regarding the nonseismic and far-field effects of tsunamis generated by volcanic eruptions. [ABSTRACT FROM AUTHOR]

The explosive eruption of the Hunga Tonga-Hunga Ha'apai volcano on 15 January 2022 generated atmospheric waves traveling around the Earth, which caused ionospheric disturbances on various spatio-temporal scales. A HF Doppler sounding system in Japan detected characteristic ionospheric disturbances showing periodic oscillations in the Doppler frequency with a period of ~ 4 min. In this study, such periodic oscillations were examined by comparing Doppler frequency data with Total Electron Content data obtained by Global Navigation Satellite System. The observed periodic oscillations in the Doppler frequency were characterized by a sawtooth or S-letter shaped variation, implying the passage of the traveling ionospheric disturbances through the reflection points of the HF Doppler sounding system. It was also found that the periodic oscillations occurred prior to the arrival of the tropospheric Lamb wave excited by the Tonga eruption. From the total electron content data, the traveling ionospheric disturbances causing the periodic oscillations were excited by the tropospheric Lamb waves at the conjugate point in the southern hemisphere, namely, the electric field perturbations due to the Lamb waves in the southern hemisphere mapped onto the sensing area of the HF Doppler sounding system in the northern hemisphere along the magnetic field lines. The periodic oscillations were observed only in the path between Chofu transmitter and Sarobetsu receiver, whose the radio propagation path is almost aligned in the north–south direction. This suggests that the traveling ionospheric disturbance has a structure elongating in the meridional direction. The variation in the Doppler frequency was reproduced by using a simple model of the propagation of the traveling ionospheric disturbances and the resultant motion of the reflection point. As a result, the vertical motion of the reflection point associated with the periodic oscillations was estimated to be about 1 km. It is known that 4-min period variations are sometimes observed in association with earthquakes, which is due to resonances of acoustic mode waves propagating between the ground and the lower ionosphere. Therefore, a similar resonance structure in the southern hemisphere is a plausible source of the traveling ionospheric disturbances detected in the northern hemisphere. [ABSTRACT FROM AUTHOR]

The 2022 Hunga Tonga-Hunga Ha'apai eruption generated tsunamis that propagated across the Pacific Ocean. Along the coast of Japan, nearshore amplification led to amplitudes of nearly 1 m at some locations, with varying peak tsunami occurrence times. The leading tsunami wave can generally be reproduced by Lamb waves, which are a type of air-pressure wave generated by an eruption. However, subsequent tsunamis that occurred several hours after the leading wave tended to be larger for unknown reasons. This study performs multi-scale numerical simulations to investigate subsequent tsunami waves in the vicinity of Japan induced by air pressure waves caused by the eruption. The atmospheric pressure field was created using a dispersion relation of atmospheric gravity wave and tuned by physical parameters based on observational records. The tsunami simulations used the adaptive mesh refinement method, incorporating detailed bathymetry and topography to solve the tsunami at various spatial scales. The simulations effectively reproduced the tsunami waveforms observed at numerous coastal locations, and results indicate that the factors contributing to the maximum tsunami amplitude differ by region. In particular, bay resonance plays a major role in determining the maximum amplitude at many sites along the east coast of Japan. However, large tsunami amplification at some west coast locations was not replicated, probably because it was caused by amplification during oceanic wave propagation rather than meteorological factors. These findings enhance our understanding of meteotsunami complexity and help distinguish tsunami amplification factors. [ABSTRACT FROM AUTHOR]

In this study, we detected the horizontal ground strains induced by the atmospheric Lamb wave emitted from the 2022 eruption of the Tonga–Hunga Ha'apai undersea volcano, at an underground observatory in Kamioka, Japan. The observed strains were in the range of 10 - 11 – 10 - 10 and were measured precisely using a 1500-m laser strainmeter with a high resolution in the order of 10 - 12 . This was one of the first observations of a Lamb wave using a laser strainmeter. The strainmeter was constructed in a tunnel of the KAGRA gravitational-wave telescope. Our observations demonstrate that strain and atmospheric pressure were clearly correlated, resulting in a regression coefficient of - 2.3 - 3.7 × 10 - 10 strain/hPa. This finding was compared with the responses under regular pressure conditions and the estimations obtained using the local deformation and traveling wave models. The observed coefficients for the Lamb wave exhibited smaller magnitudes than those observed under regular conditions and take values between that of the two theoretical models. These results reflect the intermediate scale of the pressure distribution of the Lamb wave between the assumptions of the simple models. The strain variations were also found to have started earlier than the corresponding pressure changes at the observation site with characteristic time lags ranging from 25 to 155 s. In addition, several aspects related to the mechanism that created the time lags are discussed. [ABSTRACT FROM AUTHOR]

The eruption of the Hunga Tonga–Hunga Ha'apai volcano on 15 January 2022 was the first powerful explosive eruption in history to be recorded with high quality by a wide range of geophysical equipment. The atmospheric Lamb wave caused by the explosion repeatedly circled the Earth and served as one of the reasons for the formation of tsunami waves. In this paper, the Lamb wave manifestations are analyzed in the recordings of tsunamimeters, i.e., in data from DONET and DART pressure sensors located in the area of the Japanese Islands. The work is aimed at studying the physics of the formation of pressure variations at the ocean floor in order to develop a method for isolating free gravity waves in records obtained by bottom pressure sensors. Within the framework of shallow water theory, an analysis of the response of the water layer to the atmospheric Lamb wave was performed. This response combines a forced perturbation, the amplitude of which depends on the depth of the ocean, and free gravity waves arising as a result of the restructuring of the forced perturbation on the submarine slopes. Analytical formulas are given for the amplitude and energy of the forced perturbation and free waves arising at the depth jump. With the aid of numerical simulation, the finite length of a slope was revealed to significantly affect the parameters of free waves when exceeding 50 km. The analysis of in situ data (DONET, DART) confirms the validity of theoretical concepts presented in the work. In particular, it is shown that variations of bottom pressure in the deep ocean exceed the amplitude of atmospheric pressure fluctuations in the Lamb wave. [ABSTRACT FROM AUTHOR]

The 2022 eruption of the Hunga Tonga-Hunga Ha'apai volcano excited an atmospheric Lamb wave, which induced a fast-traveling tsunami. This tsunami was driven by the pressure-forced wave traveling at the speed of the Lamb wave and, thus, was much faster than conventional tsunamis. This was the first case in which ocean bottom monitoring systems widely observed an air pressure-induced tsunami. We found that the pressure-forced waves split and generated ocean gravity waves after passing the Japan Trench based on the S-net data. Our simulations show that changes in water depth can amplify or decrease the pressure-forced wave. Simultaneously, an ocean gravity wave is generated due to the conservation of water volume. Because the ocean gravity wave was slower than the pressure-forced wave near Japan, it was separated from, and traveled behind, the pressure-forced wave. We explained the wave separation phenomenon and reproduced the waveforms of different splitting stages observed by the stations near the Japan Trench. [ABSTRACT FROM AUTHOR]

The explosive 2022 Tonga submarine volcanic eruption produced a globally propagated atmospheric disturbance. A leading Lamb wave pulse was recorded as a pressure pulse worldwide. A weather‐station network in Japan recorded the pressure pulse together with temperature and wind conditions during the passage of the pulse. Individual temperature and wind records indicate little simultaneous change. However, after alignment of records at the time of pressure pulse arrivals and stacking, clear temperature and wind changes synchronized with the pressure change are evident. Assuming Lamb wave propagation, the synthesized temperature and wind changes from the pressure record show a good match with the observed waveforms. The observed wind speed and pressure change of the Lamb pulse yielded a total energy transported by the pulse of 4.2 × 1016 J. Plain Language Summary: Atmospheric disturbance caused by the violent 2022 Tonga volcanic eruption was recorded by multiple types of sensors on the ground. The leading pressure signals, of about 20 min duration and about 2 hPa amplitude, were observed in a nationwide weather network in Japan as an anomaly that stands out from the background atmospheric pressure trend. Other meteorological sensors such as temperature and wind components were also in operation, but expected changes are on the order of 0.15 K and 0.5 m/s over the 20 min signal duration, too small to be detected in individual records. Using a pressure signal as a time mark for data alignment, we averaged all temperature and wind components parallel to the direction from Tonga toward Japan recorded by the network. Such averaging steps greatly reduced the spatially incoherent background noise and enhanced the signals coherent with the arrival of the pressure pulse. The resultant temperature and wind changes are comparable to the theoretically predicted ones. The measured temporal changes of atmospheric pressure and air flow enable direct estimation of the energy flow transported by the pressure pulse. The estimated total energy transported by the pressure pulse is between (3.8–4.6) × $\times $ 1016 J. Key Points: Stacking nationwide weather network records reveals temporal changes in temperature and wind flow synchronized with the Lamb pressure pulseObserved temporal variations are close to the adiabatic air compression and Lamb wave flow models expected from the pressure pulseAnalysis of observed wind speed and pressure changes reveals that the total energy transported by the Lamb pulse was 4.2 × 1016 J [ABSTRACT FROM AUTHOR]

Meteotsunamis (forced waves) triggered by atmospheric disturbances of Lamb waves due to the 2022 Hunga–Tonga volcanic eruption have been observed in coastal areas surrounding the Pacific Ocean. However, the spatiotemporal evolution of the wavefield of meteotsunamis and meteotsunami-induced free waves remains elusive. Here, we show the detailed spatial distribution of the propagation velocities and directions of these waves in the bathymetric slope area between the Japan Trench and nearshore, using a dense array of 150 absolute pressure gauges deployed at water depths of 100–8000 m. Records show that free wave components (i.e., tsunamis) were generated when the forced wave was propagating over the slope area. Amplitudes of the generated free waves are large in the southern half of the slope area, where the equi-arrival time contour lines are densely paralleled. Such amplifications occur due to the relationship between the incoming direction of Lamb waves and the gradient of the bathymetric slope. This indicates that, if meteotsunamis excited by Lamb waves due to future volcanic eruptions come from different directions to this region, a different spatial pattern of free wave amplification on a regional scale is obtained in the bathymetric slope areas. [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]

A large eruption occurred on Jan. 15, 2022, at the submarine volcano Hunga Tonga-Hunga Ha'apai, southern Pacific, and the atmospheric Lamb wave was observed to have traveled round the Earth multiple times with a speed of ~ 0.3 km/s. Here, I compare their ionospheric and atmospheric signatures using data from dense arrays of barometers and GNSS stations in Japan. I confirmed that the ionospheric disturbances passed over Japan at least four times, first from SE to NW, then from NW to SE, again from SE to NW, and finally from NW to SE. The propagation velocity of the ionospheric disturbances was as fast as the atmospheric Lamb wave, suggesting their origin as upward energy leakage from the troposphere. The first passage of the ionospheric disturbance started prior to the arrival of the Lamb pulse, but its physical mechanism is yet to be explored. Unlike the barometric records, waveforms and amplitudes of ionospheric disturbances exhibit large diversity along the wavefront, suggesting their turbulent nature. [ABSTRACT FROM AUTHOR]

To elucidate the characteristics of electromagnetic conjugacy of traveling ionospheric disturbances just after the 15 January 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption, we analyze Global Navigation Satellite System-total electron content data and ionospheric plasma velocity data obtained from the Super Dual Auroral Radar Network Hokkaido pair of radars. Further, we use thermal infrared grid data with high spatial resolution observed by the Himawari 8 satellite to identify lower atmospheric disturbances associated with surface air pressure waves propagating as a Lamb mode. After 07:30 UT on 15 January, two distinct traveling ionospheric disturbances propagating in the westward direction appeared in the Japanese sector with the same structure as those at magnetically conjugate points in the Southern Hemisphere. Corresponding to these traveling ionospheric disturbances with their large amplitude of 0.5 – 1.1 × 1016 el/m2 observed in the Southern Hemisphere, the plasma flow direction in the F region changed from southward to northward. At this time, the magnetically conjugate points in the Southern Hemisphere were located in the sunlit region at a height of 105 km. The amplitude and period of the plasma flow variation are ~ 100–110 m/s and ~ 36–38 min, respectively. From the plasma flow perturbation, a zonal electric field is estimated as ~ 2.8–3.1 mV/m. Further, there is a phase difference of ~ 10–12 min between the total electron content and plasma flow perturbations. This result suggests that the external electric field variation generates the traveling ionospheric disturbances observed in both Southern and Northern Hemispheres. The origin of the external electric field is an E-region dynamo driven by the neutral wind oscillation associated with atmospheric acoustic waves and gravity waves. Finally, the electric field propagates to the F region and magnetically conjugate ionosphere along magnetic field lines with the local Alfven speed, which is much faster than that of Lamb mode waves. From these observational facts, it can be concluded that the E-region dynamo electric field produced in the sunlit Southern Hemisphere is a main cause of the two distinct traveling ionospheric disturbances appearing over Japan before the arrival of the air pressure disturbances. [ABSTRACT FROM AUTHOR]

To elucidate the characteristics of electromagnetic conjugacy of traveling ionospheric disturbances just after the 15 January 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption, we analyze Global Navigation Satellite System-total electron content data and ionospheric plasma velocity data obtained from the Super Dual Auroral Radar Network Hokkaido pair of radars. Further, we use thermal infrared grid data with high spatial resolution observed by the Himawari 8 satellite to identify lower atmospheric disturbances associated with surface air pressure waves propagating as a Lamb mode. After 07:30 UT on 15 January, two distinct traveling ionospheric disturbances propagating in the westward direction appeared in the Japanese sector with the same structure as those at magnetically conjugate points in the Southern Hemisphere. Corresponding to these traveling ionospheric disturbances with their large amplitude of 0.5 – 1.1 × 1016 el/m2 observed in the Southern Hemisphere, the plasma flow direction in the F region changed from southward to northward. At this time, the magnetically conjugate points in the Southern Hemisphere were located in the sunlit region at a height of 105 km. The amplitude and period of the plasma flow variation are ~ 100–110 m/s and ~ 36–38 min, respectively. From the plasma flow perturbation, a zonal electric field is estimated as ~ 2.8–3.1 mV/m. Further, there is a phase difference of ~ 10–12 min between the total electron content and plasma flow perturbations. This result suggests that the external electric field variation generates the traveling ionospheric disturbances observed in both Southern and Northern Hemispheres. The origin of the external electric field is an E-region dynamo driven by the neutral wind oscillation associated with atmospheric acoustic waves and gravity waves. Finally, the electric field propagates to the F region and magnetically conjugate ionosphere along magnetic field lines with the local Alfven speed, which is much faster than that of Lamb mode waves. From these observational facts, it can be concluded that the E-region dynamo electric field produced in the sunlit Southern Hemisphere is a main cause of the two distinct traveling ionospheric disturbances appearing over Japan before the arrival of the air pressure disturbances. [ABSTRACT FROM AUTHOR]

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]

The major eruption of volcano Hunga Tonga‐Hunga Ha'apai in Tonga on 15 January 2022 generated atmospheric Lamb waves that propagated over the world. This seemed the first volcanic Lamb wave event that was clearly captured by the state‐of‐the‐art geostationary meteorological satellites. This paper provides visualization of the waves using thermal infrared images from geostationary satellite Himawari‐8. The second time derivatives of 10‐min interval images clearly illustrated the waves propagating at about 310 m s−1. The waves could be tracked for more than a week while they propagated five times round the earth. Automated wavefront identification illustrated nonuniform propagation speed. The signals in the satellite images well matched the surface pressure observations in Japan. Plain Language Summary: The major eruption of volcano Hunga Tonga‐Hunga Ha'apai in Tonga on 15 January 2022 generated atmospheric pressure pulses that propagated over the world. This seemed the first event that was clearly captured by the state‐of‐the‐art geostationary meteorological satellites, such as Himawari‐8. Taking the time difference of Himawari‐8's 10‐min interval images twice, the waves that propagated at about 310 m s−1 could be tracked for more than a week while they propagated five times round the earth. This was not possible with the previous‐generation geostationary meteorological satellites. Visualized waves also illustrated how the propagation speed changes in space and time. The signals in the satellite images well matched the surface pressure observations in Japan. Key Points: Lamb waves from an eruption were clearly visualized by the second time derivative of satellite infrared images every 10 minThe waves could be tracked for more than a week while they propagated at least five times round the earth at a speed of about 310 m s−1The signals in the satellite images matched the surface pressure changes quantitatively [ABSTRACT FROM AUTHOR]

The violent eruption of Hunga Tonga-Hunga Ha'apai volcano on January 15, 2022 induced strong atmospheric disturbances, which traveled around the world as atmospheric Lamb waves. When this wave passed through the superconducting gravimeter station at Matsushiro, Japan, a large signal of gravity changes was recorded. Also, barometers installed around Matsushiro recorded wave trains of pressure changes. Analysis of the barometer data revealed that the atmospheric disturbances traveled as plane waves. Applying the theory of atmospheric loading for traveling plane waves, the observed gravity changes were well reproduced by a sum of three components of atmospheric loading, namely, Newtonian, free-air and inertial effects. In particular, the inertial effect of atmospheric loading, which is rarely observed, was clearly identified in the gravity data. From the theoretical modeling, an estimate of rigidity in the shallow region of the Earth was also obtained. [ABSTRACT FROM AUTHOR]

Large-amplitude meteotsunamis were observed in many areas in Japan, following the arrival of barometric Lamb waves emitted by an underwater volcanic eruption of Hunga Tonga-Hunga Ha'apai in January 2022. We modeled the power spectra of the tidal level data obtained from 12 tide stations of the Geospatial Information Authority of Japan, based on a method of transfer function which converts the barometric pressure pulse spectra into the meteotsunami spectra. The obtained transfer functions are similar at 12 stations. The pressure pulse spectra are obtained from the ensemble average of ~1500 Soratena weather sensors of Weathernews Inc. distributed over Japan. The observed meteotsunami spectra can be characterized by the enhanced seiche eigenmodes at each station excited by the mesoscale pressure pulse within the amplitude error of 50%, which contributes for accumulating the necessary knowledge to understand the potential dangers in various different areas over Japan. [ABSTRACT FROM AUTHOR]