Gyroscopic waves in the Mediterranean Sea

In the ocean outside areas of dense‐water formation, coherent vertical motions (w) are generally much weaker (∼10 −3 ) than horizontal (u, v) ones. According to theoretical models based upon “the traditional approximation”, i.e. where the horizontal component of the Coriolis force is neglected, describing inertio‐gravity waves in the ocean interior, this holds especially for motions at the inertial frequency f: w(f) < O(10 −2 (u(f),v(f))). We present observations of significant w(f), with mean values of 10 −1 (u(f),v(f)) and occasional values of 1(u(f),v(f)), from the deep Western Mediterranean Sea characterized by very small buoyancy frequency N = 0 ± 0.4f. Our observations also present evidence of vertical propagation of internal waves, originated in the near‐surface density stratified layers, through homogeneous layers below. The observations could be interpreted only within the framework of “non‐traditional approach” with the horizontal component of the Coriolis force fully taken into account.