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Based on the barometric data recorded by the seismic monitoring network on the Chinese mainland, Lamb wave periods and relative arrival times of 462 stations are obtained with the aid of Meyer's wavelet decomposition, Welch's periodogram spectrum estimation and waveform cross-correlation. By extracting the seismic Rayleigh waves of two seismic stations in the South Pacific and comparing them with the synthetic seismograms, the occurrence time of the first two large volcanic eruptions and the largest volcanic eruption are credibly deduced, and then the travel times and propagation speeds of the Lamb waves are obtained. In order to further explain the attributes of the pressure disturbance associated with the complex acoustic gravity wave (AGW) phases on pressure, a series of numerical simulations with the QSSP program are applied to yield highly similar waves corresponding to the barometric records, which indicates that the eruption source may contain more than 10 sub-events within an hour. According to our detailed analyses, major conclusions are obtained as follows: (1) Although the primary pressure disturbance of the Tonga volcanic eruption appears to be a simple bulge, it is in fact a complex wave composed of multiple eruptions. The largest eruption occurred about 13 min after the first large eruption. (2) In addition to the propagation of the traditional Lamb mode, the Pekeris mode phase that propagates with a lower speed is also observed in some stations, and its amplitude is about a fifth of the Lamb wave. The Pekeris waves may have been more significantly delayed as they traveled against the westerly wind due to their much shorter periods and lower velocities. (3) The group velocity of the Lamb wave is about 308 m/s. Its average period is 70 min, and the wavelength is about 1300 km. The arrival time deviation at each station is negatively correlated with the difference in the near-surface air temperature between North and South China. However, accurately estimating the parameters of the Pekeris waves or the antipodal Lamb waves is challenging due to their low signal-to-noise ratio (SNR), even though the horizontal propagation speed of the Pekeris wave toward China is estimated to be approximately 225 m/s. (4) Much shorter periods and later arrivals at the stations within 200 km of Beijing may be related to the significant cooling (i.e. 12 °C temperature drop), which occurred from Ulantoba, Outer Mongolia, to Beijing beginning at noon on January 15 (Beijing time). [ABSTRACT FROM AUTHOR]

At 12:15 on January 15, 2022 (Beijing time), a massive eruption of the Hunga Tonga-Hunga Ha'apai volcano produced violent atmospheric fluctuations, which in turn generated a global tsunami through an abrupt air pressure shock upon the sea surface. Two main components of tsunami waves, phase-locked waves and free gravity waves, were identified by significant differences in propagating speeds across the deep ocean. The phase-locked wave propagated through the ocean basin synchronously with the atmospheric Lamb wave at an average speed of approximately 306 m/s, followed by the free gravity wave at a slower speed. The locked wave reached the coast of eastern Taiwan Island at about 20:00 on January 15, in coincidence with the Lamb wave arrival. However, on the coast of Chinese mainland, tidal gauges did not record tsunami signals until at least 2 h after the Lamb wave arrivals. Theoretical analyses and numerical experiments both suggested that as a result of the incoming wave shoaling above the vast continental shelf of Chinese mainland, the locked wave was no longer trapped by the air pressure shock and gradually transformed into freely-propagating shallow water waves by slowing down its propagation. Due to the long-lasting planetary atmospheric fluctuations circling the earth many times, the sea level oscillations continuously propagated onto the Chinese shelf, which resulted in the tsunami waves excited along the Chinese coasts for at least 36 h. The maximum wave amplitude recorded on the coast of eastern Taiwan Island was 44 cm at Wushi, while on the coasts of eastern and southern Chinese mainland, the maximum amplitudes were 22 cm at Shipu and 13 cm at Zhuhai. Fourier and wavelet analyses were performed to identify the major components of the tsunami waves on the Chinese coasts. The results indicated that eastern Taiwan Island was impacted mainly by the waves with periods of approximately 10–40 min. Chinese mainland was hit by the evolved shallow water waves and subsequent free waves, with periods of approximately 40–100 and 16–20 min, respectively. [ABSTRACT FROM AUTHOR]