Shear, Strain and Thermohaline Vertical Fine Structure in the Upper Ocean

摘要

Observations of fine scale (1-100m) vertical shear, strain and thermohalinestructure are interpreted in terms of internal wave and frontal zone dynamics. The date were collected with the Marine Physical Laboratory 161 kHz Doppler sonar and a pair of CTD's. The two systems were operated from R/P FLIP for 18 days during February-March, 1990, as part of the SWAPP (35 deg N, 127 deg W) experiment. These simultaneous measurements of velocity and density provide an unique opportunity to study the vertical advection of shear layers. The observed shear variance is dominated by near inertial waves, with 35 m vertical wavelengths. These inertial waves propagate down from the mixed layer and are vertically advected by higher frequency waves. Vertical wavenumber-frequency spectral of shear and strain are examined in Eulerian (fixed depth) and semi-Langrangian (isopyncal following) coordinates. The semi-Langrangian shear and strain variances are more consistent with variances modeled by a linear superposition of internal waves. The p.d.f.'s of buoyancy frequency and Froude number (buoyancy normalized shear) are determined using the kinematic strain model of Pinkel and Anderson (1992). The Froude number distribution shows good agreement with data presented here and historical data (PATCHEX; Kunze et al., 1990). The advection of a frontal zone past the experiment site yielded detailed observations of frontal interleaving. Two vertical interleaving scales am observed.