Asymmetric vertical internal wave propagation

Yearlong data from a single ADCP above the northern extension of the Mid‐Atlantic Ridge are used to investigate vertical internal wave propagation in the open ocean (395–1025 m). Whilst 80% of incoherent semidiurnal tidal (D 2 ) phase propagates downward, 90% of near‐inertial (f) phase propagates upward. Most upward propagating f‐phase is found at sub‐f frequencies σ min (N = f) ≈ 0.74f < σ ≤ 0.99f, N the buoyancy frequency and σ min the lower bound of the inertio‐gravity (IG) wave band following the ‘non‐traditional approach’, which includes the horizontal component of the Earth's rotation in momentum equations. The upper bound of mostly downward propagating D 2 ‐phase coincides with the upper IG‐bound σ max (N = f) ≈ 1.35f. The limited band [σ min , σ max ] demonstrates that f and D 2 contain special internal waves concerning vertical propagation. It is suggested that this is partially attributable to small‐scale step layering in N, with N = f separating ‘trapping’ from ‘classic propagating’ wave regimes, rendering the mean large‐scale N ≈ 18f less important.