Mesoscale eddies are a dominant source of spatial variability in the surface ocean and play a major role in the biological marine carbon cycle. Satellite altimetry is often used to locate and track eddies, but this approach is rarely validated against in situ observations. Here we compare measurements of a small (under 25 km radius) mode water anticyclonic eddy over the Procupine Abyssal Plain using CTD and ADCP measurements from 3 ships, 2 gliders, 2 profiling floats, and one Lagrangian float with those derived from sea level anomaly. In situ estimates of the eddy center were estimated from maps of the thickness of its central isopycnal layer, from ADCP velocities at a reference layer, and from the trajectory of the Lagrangian float. These were compared to three methods using altimetric SLA: one based on maximizing geostrophic rotation, one based on a constant SLA contour, and one which maximizes geostrophic velocity speed along the eddy boundary. All algorithms were used to select CTD profiles that were within the eddy. The in-situ metrics agreed to 97\%. The altimetry metrics showed only a small loss of accuracy, giving $>90$\% agreement with the in situ results. This suggests that current satellite altimetry is adequate for understanding the spatial representation of even relatively small mesoscale eddies.

A fleet of surface drifters (SWIFTs) equipped with down-looking high-resolution ADCPs were used to estimate the turbulent kinetic energy (TKE) dissipation rate (ε) within highly stratified diurnal warm layers (DWLs) in the Southern California bight. Over a 10-day period, five instances of DWLs were observed with strong surface temperature anomalies up to 3 °C and velocity anomalies up to 0.3 m s-1. Profiles of ε in the upper 5 meters suggest turbulence is strongly modulated by the DWL stratification. Burst-averaged (8.5 minutes) ε is stronger than predicted by law-of-the-wall boundary layer scaling within the DWL and suppressed below. Predictions for ε within the DWL are improved by a shear-production scaling using observed shear and linearly decaying turbulent stress. However, ε is still under-predicted. Examination of the un-averaged acoustic backscatter data suggests elevated ε is related to the presence of turbulent structures in the DWL which span the layer height and strongly modulate TKE. Evolution in the bulk Richardson number each day suggests the DWLs become unstable to layer-scale overturning and entrainment each afternoon, thus the turbulent structures may result from shear-driven instability. This interpretation is supported by a conditional average of the data during a burst characterized by strongly periodic structures. The structures resemble high-frequency internal waves with strong asymmetry in the along-flow direction (steepening) which suggests they are unstable. Coincident asymmetric patterns in upwelling/downwelling and corresponding regions of strong vertical convergence/divergence suggest both vertical transport and local TKE generation are plausible sources of elevated ε in the DWL.

Two moorings deployed for 75 days in 2019 and long-term satellite altimetry data reveal a spatially complex and temporally variable internal tidal field at the SWOT Cal/Val site off central California due to the interference of multiple seasonally-variable sources. Coherent tides account for $\sim$45\% of the potential energy. The south mooring exhibits more energetic semidiurnal tides, while the north mooring displays stronger mode-1 M$_2$ with an amplitude of $\sim$5.1 mm. These findings from in situ observations align with the analysis of 27-year altimetry data. The altimetry results indicate that the complex internal tidal field is attributed to multiple sources. Mode-1 tides primarily originate from the Mendocino Ridge and the 36.5\textendash37.5$^\circ$N California continental slope, while mode-2 tides are generated by local seamounts and Monterey Bay. The generation and propagation of these tides are influenced by mesoscale eddies and seasonal stratification. Seasonality is evident for mode-1 waves from three directions. Southward components from the Mendocino Ridge consistently play a dominant role ($\sim$268 MW) yearlong. We observed the strongest eastward waves during the fall and spring seasons, generated remotely from the Hawaiian Ridge. Westward waves from the 36.5\textendash37.5$^\circ$N California continental slope are weakest during summer, while those from the Southern California Bight are weakest during spring. The highest variability of energy flux is found in the westward waves ($\pm 22\%$), while the lowest is in the southward waves ($\pm 13\%$). These findings emphasize the importance of incorporating the seasonality and spatial variability of internal tides for the SWOT internal tidal correction.

Turbulent flow in surface layer, the top few meters in the ocean, tends to exhibit consistent and repeatable characteristics, and useful empirical laws can be formed to shed light on turbulence parameterization. Here, Monin-Obukhov similarity theory (MOST), developed for the atmospheric surface layer, is examined for the ocean surface layer. Using data collected from several moored surface flux buoys, we consider the relationship between surface fluxes and subsurface temperature gradients under a wide range of stability conditions. Large deviations from MOST predictions are found in our analysis, with smaller observed temperature gradients under both stable and unstable forcing. We hypothesize that these are attributed to the presence of Langmuir structures through interaction of Eulerian current with Stokes drift, which is not included in traditional Monin-Obukhov formulation. We examine the ability of recent Langmuir turbulence closure models to predict the observed differences.

Mixing in the ocean interior clearly draws its energy from the internal wave field. The pathway is often described as “Internal wave breaking“, contrary to the observation that the smallest vertical internal wave scales are larger than the largest turbulence scales. Evidence for a different pathway is reviewed here: Internal waves generate patches of LAST, “layered stratified turbulence”, a well-characterized class of motions distinct from internal waves and three-dimensional turbulence. LAST dominates the dynamics in the ‘–1’ range of vertical wavenumbers between internal waves and turbulence. It is possibly generated at transient critical layers, cascades energy to smaller scales and dissipates by generating patches of turbulence and mixing through shear instability. The existence of such patches is well-documented and the limited data suggests that they produce most of the mixing. The mixing efficiency is set by the properties of LAST, not the properties of internal waves.