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

High-resolution observations of the North Pacific transition layer from a Lagrangian float

Kaminski, A.K., E.A. D'Asaro, A.Y. Shcherbina, and R.R. Harcourt, "High-resolution observations of the North Pacific transition layer from a Lagrangian float," J. Phys. Oceanogr., EOR, doi:10.1175/JPO-D-21-0032.1, 2021.

More Info

2 Aug 2021

A crucial region of the ocean surface boundary layer (OSBL) is the strongly-sheared and -stratified transition layer (TL) separating the mixed layer from the upper pycnocline, where a diverse range of waves and instabilities are possible. Previous work suggests that these different waves and instabilities will lead to different OSBL behaviours. Therefore, understanding which physical processes occur is key for modelling the TL. Here we present observations of the TL from a Lagrangian float deployed for 73 days near Ocean Weather Station Papa (50°N, 145°W) during Fall 2018. The float followed the vertical motion of the TL, continuously measuring profiles across it using an ADCP, temperature chain and salinity sensors. The temperature chain made depth/time images of TL structures with a resolution of 6 cm and 3 seconds. These showed the frequent occurrence of very sharp interfaces, dominated by temperature jumps of O(1)°C over 6 cm or less. Temperature inversions were typically small (less than about 10 cm), frequent, and strongly-stratified; very few large overturns were observed. The corresponding velocity profiles varied over larger length scales than the temperature profiles. These structures are consistent with scouring behaviour rather than Kelvin–Helmholtz-type overturning. Their net effect, estimated via a Thorpe-scale analysis, suggests that these frequent small temperature inversions can account for the observed mixed layer deepening and entrainment flux. Corresponding estimates of dissipation, diffusivity, and heat fluxes also agree with previous TL studies, suggesting that the TL dynamics is dominated by these nearly continuous 10-cm scale mixing structures, rather than by less frequent larger overturns.

Evaluating Monin–Obukhov scaling in the unstable oceanic surface layer

Zheng, Z., R.R. Harcourt, and E.A. D'Asaro, "Evaluating Monin–Obukhov scaling in the unstable oceanic surface layer," J. Phys. Oceanogr., 51, 911–930, doi:10.1175/JPO-D-20-0201.1, 2021.

More Info

1 Mar 2021

Monin–Obukhov Similarity Theory (MOST) provides important scaling laws for flow properties in the surface layer of the atmosphere and has contributed to most of our understanding of the near-surface turbulence. The prediction of near-surface vertical mixing in most operational ocean models is largely built upon this theory. However, the validity of MOST in the upper ocean is questionable due to the demonstrated importance of surface waves in the region. Here we examine the validity of MOST in the statically unstable oceanic surface layer, using data collected from two open ocean sites with different wave conditions. The observed vertical temperature gradients are found to be about half of those predicted by MOST. We hypothesize this is attributable to either the breaking of surface waves, or Langmuir turbulence generated by the wave-current interaction. Existing turbulence closure models for surface wave breaking and for Langmuir turbulence are simplified to test these two hypotheses. Although both models predict reduced temperature gradients, the simplified Langmuir turbulence model matches observations more closely, when appropriately tuned.

Bulk, spectral and deep water approximations for Stokes drift: Implications for coupled ocean circulation and surface wave models

Liu, G.Q., N. Kumar, R. Harcourt, W. Perrie, "Bulk, spectral and deep water approximations for Stokes drift: Implications for coupled ocean circulation and surface wave models," J. Adv. Model. Earth Syst., 13, doi:10.1029/2020MS002172, 2021.

More Info

22 Feb 2021

Surface waves modify upper ocean dynamics through Stokes drift related processes. Stokes drift estimated from a discrete wave spectrum is compared to Stokes drift approximations as a monochromatic profile based on bulk surface wave parameters, and to two additional superexponential functional forms. The impact of these different methods on ocean processes is examined in two test‐bed cases of a wave‐current coupled system: (1) a wind‐free shallow water inlet test case and (2) an idealized deep water hurricane case with high varying winds. In case (1), tidal currents and bathymetry can modify the waves and significantly affect Stokes drift computed from the wave spectrum. In case (2), rapid variation in atmospheric stress at high wind speed generates large departures from fully developed equilibrium seas. In both cases, large deviations in ocean current response are produced when the Stokes drift is approximated monochromatically from bulk wave parameters, rather than from integration over the wave spectra. Deep water simulations using the two superexponential approximations are in better agreement with those estimated from wave spectra than are those using the monochromatic, exponential profile based on bulk wave parameters. In order to represent the impact of Stokes drift at resolved scales, we recommend that for studies of nearshore processes and deep water events, like wave‐current interactions under storms, the Stokes drift should be calculated from full wave spectra. For long simulations of open ocean dynamics, methods using superexponential profiles to represent equilibrium wind seas might be sufficient, but appear to be marginally more computationally efficient.

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