APL-UW Home

Jobs
About
Campus Map
Contact
Privacy
Intranet

Ramsey Harcourt

Principal Oceanographer

Email

harcourt@apl.washington.edu

Phone

206-221-4662

Research Interests

Large Eddy Simulation (LES), Computational Fluid Dynamics, Deep Convection, Wave and Ice Boundary Layers, Response of Drifters to Convection

Department Affiliation

Ocean Physics

Education

B.S. Physics, Reed College, 1987

M.S. Physics, University of California - Santa Cruz, 1989

Ph.D. Physics, University of California - Santa Cruz, 1999

Publications

2000-present and while at APL-UW

Small-scale dispersion in the presence of Langmuir circulation

Chang, H., and 12 others including R.R. Harcourt, "Small-scale dispersion in the presence of Langmuir circulation," J. Phys. Oceanogr., 49, 3069-3085, doi:10.1175/JPO-D-19-0107.1, 2019.

More Info

1 Dec 2019

We present an analysis of ocean surface dispersion characteristics, on 1–100 m scales, obtained by optically tracking a release of O (600) bamboo plates for 2 hours in the Northern Gulf of Mexico. Under sustained 5–6 m/s winds, energetic Langmuir cells are clearly delineated in the spatially dense plate observations. Within 10 minutes of release, the plates collect in windrows with 15 m spacing aligned with the wind. Windrow spacing grows, through windrow merger, to 40 m after 20 minutes and then expands at a slower rate to 50 m. The presence of Langmuir cells produces strong horizontal anisotropy and scale dependence in all surface dispersion statistics computed from the plate observations. Relative dispersion in the crosswind direction initially dominates but eventually saturates, while downwind dispersion exhibits continual growth consistent with contributions from both turbulent fluctuations and organized mean shear. Longitudinal velocity differences in the crosswind direction indicate mean convergence at scales below the Langmuir cell diameter and mean divergence at larger scales. Although the second order structure function measured by contemporaneous GPS-tracked surfacedrifters drogued at ~0.5 m shows persistent r2/3 power law scaling down to 100–200 m separation scales, the second-order structure function for the very near surface plates observations has considerably higher energy and significantly shallower slope at scales below 100 m. This is consistent with contemporaneous data from undrogued surface drifters and previously published model results indicating shallowing spectra in the presence of direct windwave forcing mechanisms.

Comparing ocean surface boundary vertical mixing schemes including Langmuir turbulence

Li, Q., and 18 other including R.R. Harcourt, "Comparing ocean surface boundary vertical mixing schemes including Langmuir turbulence," J. Adv. Model. Earth Syst., 11, 3545-3592, doi:10.1029/2019MS001810, 2019.

More Info

1 Nov 2019

Six recent Langmuir turbulence parameterization schemes and five traditional schemes are implemented in a common single‐column modeling framework and consistently compared. These schemes are tested in scenarios versus matched large eddy simulations, across the globe with realistic forcing (JRA55‐do, WAVEWATCH‐III simulated waves) and initial conditions (Argo), and under realistic conditions as observed at ocean moorings. Traditional non‐Langmuir schemes systematically underpredict large eddy simulation vertical mixing under weak convective forcing, while Langmuir schemes vary in accuracy. Under global, realistic forcing Langmuir schemes produce 6% (–1% to 14% for 90% confidence) or 5.2 m (–0.2 m to 17.4 m for 90% confidence) deeper monthly mean mixed layer depths than their non‐Langmuir counterparts, with the greatest differences in extratropical regions, especially the Southern Ocean in austral summer. Discrepancies among Langmuir schemes are large (15% in mixed layer depth standard deviation over the mean): largest under wave‐driven turbulence with stabilizing buoyancy forcing, next largest under strongly wave‐driven conditions with weak buoyancy forcing, and agreeing during strong convective forcing. Non‐Langmuir schemes disagree with each other to a lesser extent, with a similar ordering. Langmuir discrepancies obscure a cross‐scheme estimate of the Langmuir effect magnitude under realistic forcing, highlighting limited understanding and numerical deficiencies. Maps of the regions and seasons where the greatest discrepancies occur are provided to guide further studies and observations.

Rain and sun create slippery layers in the Eastern Pacific Fresh Pool

Shcherbina, A.Y., E.A. D'Asaro, and R.R. Harcourt, "Rain and sun create slippery layers in the Eastern Pacific Fresh Pool," Oceanography, 32, 98-107, doi:10.5670/oceanog.2019.217, 2019.

More Info

14 Jun 2019

An autonomous Lagrangian float equipped with a high-resolution acoustic Doppler current profiler observed the evolution of upper-ocean stratification and velocity in the Eastern Pacific Fresh Pool for over 100 days in August–November 2016. Although convective mixing homogenized the water column to 40 m depth almost every night, the combination of diurnal warming on clear days and rainfall on cloudy days routinely produced strong stratification in the upper 10 m. Whether due to thermal or freshwater effects, the initial strong stratification was mixed downward and incorporated in the bulk of the mixed layer within a few hours. Stratification cycling was associated with pronounced variability of ocean surface boundary layer turbulence and vertical shear of wind-driven (Ekman) currents. Decoupled from the bulk of the mixed layer by strong stratification, warm and fresh near-surface waters were rapidly accelerated by wind, producing the well-known "slippery layer" effect, and leading to a strong downwind near-surface distortion of the Ekman profile. A case study illustrates the ability of the new generation of Lagrangian floats to measure rapidly evolving temperature, salinity, and velocity, including turbulent and internal wave components. Quantitative interpretation of the results remains a challenge, which can be addressed with high-resolution numerical modeling, given sufficiently accurate air-sea fluxes.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
Close

 

Close