Mixing in the Transition Layer during Two Storm Events

Abstract Upper-ocean dynamics analyzed from mooring-array observations are contrasted between two storms of comparable magnitude. Particular emphasis is put on the role of the transition layer, the strongly stratified layer between the well-mixed upper layer, and the deeper more weakly stratified region. The midlatitude autumn storms occurred within 20 days of each other and were measured at five moorings. In the first storm, the mixed layer follows a classical slab-layer response, with a steady deepening during the course of the storm and little mixing of the thermocline beneath. In the second storm, rather than deepening, the mixed layer shoals while intense near-inertial waves are resonantly excited within the mixed layer. These create a large shear throughout the transition layer, generating turbulence that broadens the transition layer. Details of the space–time structure of the frequencies in both short waves and near-inertial waves are presented. Small-scale waves are excited within the transition ...

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