On January 15, 2022, a powerful eruption occurred at Honga Tonga-Hunga Ha'apai volcano, Tonga, and a tsunami was generated to propagate across the Pacific Ocean. The recorded tsunami waves were both earlier and more destructive than predicted by the conventional tsunami models. In this study, we investigate the underlying mechanism of this tsunami event, which is confirmed to be a combination of the atmospheric forcing, the volcanic eruption and the local resonance. Our numerical results show that the atmospheric pressure variations induced by the volcano eruption generated early waves with small amplitudes of about 0.1 m, while the volcano eruption as a direct source, with a duration of 8 min and an ejected volume of 0.3 km3, triggered large waves propagating across the South Pacific Ocean with amplitudes of about 0.5 m. In addition, the local resonance effect resulted in extreme waves with amplitude of 0.8-1.7 m in the coastal regions. These results reasonably explain the observed facts, confirming that the 2022 Tonga tsunami was an unconventional event.

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Abstract. Hurricane Irene generated strong near-inertial currents (NICs) in ocean waters when passing over the Mid-Atlantic Bight (MAB) of the US East Coast in late August 2011. It is demonstrated that a combination of valuable field data and detailed model results can be taken advantage of to study the development and decay mechanism of this event. Numerical results obtained with the Regional Oceanic Modeling System (ROMS) are shown to agree well with the field data. Both computed and observed results show that the NICs were significant in most areas of the MAB region except in the nearshore area where the stratification was totally destroyed by the hurricane-induced strong mixing. Based on the energy budget, it is clarified that the near-inertial kinetic energy (NIKE) was mainly gained from the wind power during the hurricane event. In the deepwater region, NIKE was basically balanced by the vertical turbulence diffusion (40 %) and downward divergence (33 %), while in the continental shelf region, NIKE was mainly dissipated by the vertical turbulence diffusion (67 %) and partially by the bottom friction (24 %). Local dissipation of NIKE due to turbulence diffusion is much more closely related to the rate of the vertical shear rather than the intensity of turbulence. The strong vertical shear at the offshore side of the continental shelf led to a rapid dissipation of NIKE in this region.

Abstract. Hurricane Irene generated strong near inertial currents (NICs) in the ocean waters when passing over the Mid-Atlantic Bight (MAB) of the U. S. East Coast in late August 2011. It is demonstrated that a combination of the valuable field data with detailed model results can be exploited to study the development and decay mechanism of this event. Numerical results obtained with regional oceanic modeling system (ROMS) are shown to agree well with the field data. Both computed and observed results show that the NICs were significant in most areas of the MAB region except in the nearshore area where the stratification was totally destroyed by the hurricane-induced strong mixing. Based on the energy budget, it is clarified that the near inertial kinetic energy (NIKE) was mainly gained from the wind power during the hurricane event. In the deep water region, NIKE was basically balanced by the vertical turbulence diffusion (40 %) and downward divergence (33 %). While in the continental shelf region, NIKE was mainly dissipated by the vertical turbulence diffusion (67 %) and partially by the bottom friction (24 %). Local dissipation of NIKE due to turbulence diffusion is much more closely related to the rate of the vertical shear rather than the intensity of turbulence. The strong vertical shear at the offshore side of the continental shelf leaded to a rapid dissipation of NIKE in this region.