Observed Surface Trapping of Near-inertial Waves over the Mid-Ocean Ridge in the North Atlantic Driven By Doppler Shift
2027-01-15 16:15 (China Standard Time)
Session:Session 76 - Internal Waves and Ocean Mixing
Abstract
Wind-forced near-inertial waves (NIWs) transfer atmospheric energy into the ocean interior. Observations over the North Atlantic Mid-Ocean Ridge show that this pathway can be strongly suppressed, even in anticyclonic vorticity that typically favors downward radiation. In this study, we provide observational evidence that such surface trapping of NIWs is associated with eddy-driven Doppler shift (\(\omega_i=\omega_{obs}-\mathbf{k} \cdot \mathbf{u}\)) using nine-month mooring measurements in the mid-Atlantic ridge. The two longest energetic stages were strongly surface trapped: only 18.06% and 32.14% of near-inertial kinetic energy (NIKE) penetrated below the mixed layer, despite persistent negative vorticity and weak horizontal propagation. Scale-dependent wind work and modal decomposition show that compact 300-600 km wind forcing excited higher-mode NIWs, with modes 2-4 accounting for approximately 70% and 71% of total NIKE in Stages 1 and 2, respectively. These large horizontal wavenumbers amplified the Doppler-shift effect of eddy-induced vertical shear, lowering their mean intrinsic frequencies relative to \(f_{\mathrm{eff}}\) by 0.0114f and 0.0785f, thereby inhibiting downward propagation and redirecting wind-injected near-inertial energy toward the upper ocean. Our study highlights an eddy-mediated control on the delivery of wind-injected near-inertial energy to depth, with implications for estimates of the energy available for deep-ocean mixing.
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Jan 12–15
2027
XMAS 2027
