Longitudinal and topographic variations in North Atlantic tidal and inertial energy around latitudes 30 ± 10°N

Open ocean kinetic energy is investigated at dominant inertial and semidiurnal tidal frequencies using historic current observations from the North Atlantic Ocean, around midlatitudes. Focus is on possible energy variations due to major topography changes between the eastern (Canary) and western (Hatteras, Sohm) basins, thereby crossing the Mid‐Atlantic Ridge (MAR). While, in open basins on both sides of MAR, semidiurnal kinetic energy drops in magnitude by some 50% between latitudes 20°N < ϕ < 28°N, in agreement with TPXO‐elevation data, an even larger longitudinal dependence is observed. West of MAR, semidiurnal energy is up to 30 times less than east of it. Inertial kinetic energy is either decreasing (by a factor of 2−4) westward or more or less independent of longitude. This contrasts strongly with westward intensified near‐surface inertial energy fluxes previously found. The latter fluxes also did not show an increase (by a factor of 5−10) for 25°N < ϕ < 30°N as observed here for inertial energy in both basins. West of MAR, the internal wave background level for frequencies up to sixth diurnal is much less, by a factor of 3−10, at tidal‐inertial interaction frequencies than east of MAR. No significant atmospheric or large‐scale vorticity influence, or seasonal variations therein, is found on inertial energy content across the basin. As no individual peaks are observed at frequencies K 1 , O 1 and M 1 , S 1 , direct diurnal tidal forcing and subharmonic resonance must be accompanied by nonlinear interactions in possibly enhancing inertial energy at the critical diurnal latitude.