Trapped diurnal internal tides, propagating semidiurnal internal tides, and mixing estimates in the California Current System from sustained glider observations, 2006–2012

Abstract

From 2006–2012, along 3 repeated cross-shore transects (California Cooperative Oceanic Fisheries Investigations lines 66.7, 80, and 90) in the California Current System, 33609 shear and 39737 strain profiles from 66 glider missions are used to estimate mixing via finescale parameterizations from a dataset containing over 52000 profiles. Elevated diffusivity estimates and energetic diurnal (D1) and semidiurnal (D2) internal tides are found: (a) within 100km of the coast on lines 66.7 and 80 and (b) over the Santa Rosa-Cortes Ridge (SRCR) in the Southern California Bight (SCB) on line 90. While finding elevated mixing near topography and associated with internal tides is not novel, the combination of resolution and extent in this ongoing data collection is unmatched in the coastal ocean to our knowledge.Both D1 and D2 internal tides are energy sources for mixing. At these latitudes, the D1 internal tide is subinertial. On line 90, D1 and D2 tides are equally energetic over the SRCR, the main site of elevated mixing within the SCB. Numerous sources of internal tides at the rough topography in the SCB produce standing and/or partially-standing waves. On lines 66.7 and 80, the dominant energy source below about 100m for mixing is the D1 internal tide, which has an energy density of the D2 internal tide. On line 80, estimated diffusivity, estimated dissipation, and D1 energy density peak in summer. The D1 energy density shows an increasing trend from 2006 to 2012. Its amplitude and phase are mostly consistent with topographically-trapped D1 internal tides traveling with the topography on their right. The observed offshore decay of the diffusivity estimates is consistent with the exponential decay of a trapped wave with a mode-1 Rossby radius of 20–30km. Despite the variable mesoscale, it is remarkable that coherent internal tidal phase is found.