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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., EOR, doi:10.1175/JPO-D-19-0107.1, 2019.

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30 Sep 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.

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.

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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.

Northern Arabian Sea Circulation-Autonomous Research (NASCar): A research initiative based on autonomous sensors

Centurioni, L.R., and 33 others, including R.R. Harcourt, C.M. Lee, L. Rainville, and A.Y. Shcherbina, "Northern Arabian Sea Circulation-Autonomous Research (NASCar): A research initiative based on autonomous sensors," Oceanography, 30, 74-87, doi:10.5670/oceanog.2017.224, 2017.

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1 Jun 2017

The Arabian Sea circulation is forced by strong monsoonal winds and is characterized by vigorous seasonally reversing currents, extreme differences in sea surface salinity, localized substantial upwelling, and widespread submesoscale thermohaline structures. Its complicated sea surface temperature patterns are important for the onset and evolution of the Asian monsoon. This article describes a program that aims to elucidate the role of upper-ocean processes and atmospheric feedbacks in setting the sea surface temperature properties of the region. The wide range of spatial and temporal scales and the difficulty of accessing much of the region with ships due to piracy motivated a novel approach based on state-of-the-art autonomous ocean sensors and platforms. The extensive data set that is being collected, combined with numerical models and remote sensing data, confirms the role of planetary waves in the reversal of the Somali Current system. These data also document the fast response of the upper equatorial ocean to monsoon winds through changes in temperature and salinity and the connectivity of the surface currents across the northern Indian Ocean. New observations of thermohaline interleaving structures and mixing in setting the surface temperature properties of the northern Arabian Sea are also discussed.

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
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