Observations of tilting meddies

Abstract

SOFAR floats at different depths within two Mediterranean Water eddies (meddies) reveal that the meddy rotation axes tilt transversely with respect to the meddy translation direction. The rotation axis of one of the meddies (Meddy 1) was displaced by about 6 km over a depth of roughly 100 m; the axis of the second meddy (Meddy 2) was displaced by about 0.4 km over 100-m depth. These results are compared to a simple theoretical model that predicts the deformation and translation of a lens-shaped eddy embedded in large-scale external shear. Observed lateral deformations of the meddies are in good agreement with model predictions. The observed tilt of Meddy 1 is attributed to a combination of depth-varying rotation rate beneath the meddy core and the horizontal translation of the meddy; the tilt of Meddy 2 is attributed to a deformation of the meddy core by vertically sheared flow outside the meddy. The observed translation speed of the meddies with respect to nearby floats outside of the meddies is significantly larger than that predicted by the model.