PDF(3692 KB)
Generation and dissipation of near-inertial internal waves under the regulation of seamount width
WANG Wenbo, XIE Xiaohui
Journal of Marine Sciences ›› 2025, Vol. 43 ›› Issue (2) : 11-18.
PDF(3692 KB)
PDF(3692 KB)
Generation and dissipation of near-inertial internal waves under the regulation of seamount width
The interaction between deep-ocean geostrophic current and seamounts can generate near-inertial internal waves (NIWs). While the intensity of these waves relates to the seamount height, its dependence on seamount width remains elusive. This study employs a two-dimensional, non-hydrostatic numerical model based on MITgcm to investigate the interaction of geostrophic current with deep-sea seamounts and examine how differing seamount widths influence the generation and dissipation of NIWs. Our results demonstrate that topographic forcing triggers robust nonlinear wave-wave interactions along the summit edges on the downstream flank of the seamount. This process generates energetic near-inertial internal waves that radiate away and develop, facilitating energy transfer from the geostrophic mean flow to the NIWs. For a fixed seamount height, narrower seamounts induce stronger near-inertial waves, characterized by more rapid wave development and decay. Moreover, the downstream flank exhibits significantly enhanced vertical shears within the near-inertial internal waves, driving greater turbulent dissipation compared to the upstream flank. Therefore, our findings highlight that, in addition to seamount height, seamount width is also a critical factor governing the generation and subsequent evolution of near-inertial internal waves.
deep ocean / geostrophic current / near-inertial internal waves / turbulent mixing / current-topography interactions / nonlinear wave-wave interactions / MITgcm model / seamount width
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We review the physics of near-inertial waves (NIWs)in the ocean and the observations, theory, and models that have provided our present knowledge. NIWs appear nearly everywhere in the ocean as a spectral peak at and just above the local inertial period f, and the longest vertical wavelengths can propagate at least hundreds of kilometers toward the equator from their source regions; shorter vertical wavelengths do not travel as far and do not contain as much energy, but lead to turbulent mixing owing to their high shear. NIWs are generated by a variety of mechanisms, including the wind, nonlinear interactions with waves of other frequencies, lee waves over bottom topography, and geostrophic adjustment; the partition among these is not known, although the wind is likely the most important. NIWs likely interact strongly with mesoscale and submesoscale motions, in ways that are just beginning to be understood.
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The direct response of the tropical mixed layer to near-inertial waves (NIWs)has only rarely been observed. Here, we present upper-ocean turbulence data that provide evidence for a strongly elevated vertical diffusive heat flux across the base of the mixed layer in the presence of a NIW, thereby cooling the mixed layer at a rate of 244 W m over the 20 h of continuous measurements. We investigate the seasonal cycle of strong NIW events and find that despite their local intermittent nature, they occur preferentially during boreal summer, presumably associated with the passage of atmospheric African Easterly Waves. We illustrate the impact of these rare but intense NIW induced mixing events on the mixed layer heat balance, highlight their contribution to the seasonal evolution of sea surface temperature, and discuss their potential impact on biological productivity in the tropical North Atlantic.
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