Journal Article

Pure Inertial Waves Radiating From Low‐Frequency Flows Over Large‐Scale Topography

Chen, Zhiwu, Li, Wei, Zhang, Dongsheng, Xie, Xiaohui, Chen, Dake, Liu, Xiaohui, Wang, Yan

2023

Overview

Mooring data collected at a flat‐topped seamount suggest the generation of pure inertial waves (PIWs; waves with a dominant frequency equal to the local inertial frequency f) by low‐frequency flows over large‐scale topography. Energetic PIWs were observed within a narrow depth range (∼100 m) near the seafloor at the edge of the summit. These waves could be associated with low‐frequency flows. A two‐dimensional nonhydrostatic model was used to show that the observed PIWs are most likely internal wave beams generated by low‐frequency flows over the seamount. Two types of PIWs were identified via observation and model. The first is a PIW that can only travel horizontally. The other propagates upward, with super‐inertial intrinsic frequency that is Doppler‐shifted by the flows to f. Nonlinear triadic interactions among waves with the frequencies [0, f, f] may transfer energy from mean flows to PIWs, promoting energy decay of geostrophic flows over large‐scale topography. Plain Language Summary Near‐inertial waves (NIWs) are intrinsic motions of the ocean caused by Earth’s rotation. Understanding their generation and evolution is key to parameterizing NIWs and the associated mixing in global ocean circulation models. This study presents novel observations suggesting that energetic pure inertial waves (PIWs; i.e., NIWs with a dominant frequency appearing at the local inertial frequency) are generated by low‐frequency flows over large‐scale seamount topography in the abyssal ocean. The nonlinear forcing of low‐frequency flows due to their acceleration near the seamount summit is suggested to be essential for generating PIWs. These findings provide further insight into NIWs in the abyssal ocean, which is important for understanding the distribution of NIWs and the energy decay of geostrophic flows over topography. Key Points Energetic pure inertial waves (PIWs) were observed within a narrow depth range near the seafloor at a large abyssal seamount Near‐bottom‐enhanced PIWs stem from nonlinear forcing of low‐frequency flows over the seamount Low‐frequency flows over the seamount generate two types of PIWs: nonvertically propagating and upward‐propagating

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Abyssal zone / Decay / Doppler sonar / Earth rotation / Energy / flow‐topography interaction / Inertial waves / Internal waves / low‐frequency flows / near‐inertial waves / nonlinear triadic interactions / Ocean circulation / Ocean circulation models / Ocean currents / Ocean floor / Ocean models / Oceans / pure inertial waves / seamount / Seamounts / Topography