Upper Ocean Shear during JASIN: A Deterministic and Statistical Analysis

摘要

The shear field measured by the W1 mooring during JASIN 1978 was analyzed, using deterministic statistical approaches. A significant fraction of the shear variance was at the semidiurnal tidal frequency. In order to determine whether the shear was associated with internal wave trains propagating from single or multiple sources, the eccentricity of the shear ellipse was analyzed. During seven periods of intense shear, the minor-to-major axis ratio was consistent with the theoretically predicted ratio of 0.89 for coherent internal waves. From the orientation of the shear ellipse, the probable source of the internal tides during three intense periods was found to be the Rockall Bank. A statistical model of shear was applied two periods of the JASIN experiment. Internal wave-induced shear during Period 2 was comparable in level to that measured during MILE, but levels recorded during period 1 were 40% higher. This variability is attributed to changes in the propagation of the internal tide, associated with the evolving field of mesoscale eddies.