College of Earth, Ocean, and Atmospheric Sciences

Research Interests

Ocean Mixing - Exploring the physics of turbulence and mixing is key to our understanding of ocean dynamics. Innovative instrumentation, detailed analysis, and simple dynamical models enable us to:

• understand the generation and evolution of turbulence
• quantify irreversible fluxes of heat, salt, biology, chemicals and momentum
• identify the processes (the pathways to turbulence) which produce these fluxes
• determine the effects of turbulence on larger-scale flows.

Current Research

Physics of Ocean Mixing

Innovative instrumentation to explore dynamics down to the smallest scales of motion are crucial to understanding ocean turbulence and its effects. Some of the projects of the Ocean Mixing Group include:

• the development of a fast-response thermocouple to measure temperature fluctuations at the smallest scales.
• the analysis of highly resolved conductivity measurements to make the first direct estimates of turbulent salinity fluxes and salinity microstructure.
• the observation of internal hydraulic flows on the continental shelf which produce intense mixing and high drag. (Link to 4Mb PDF file)

RISE: River Influences on Shelf Ecosystems

RISE is a multidisciplinary effort to study physical and biogeochemical interactions in the complex Columbia River Plume ecosystem. Detailed observations reveal intense fronts, large-amplitude internal waves, shear-driven mixing, and intense bottom boundary layers. Visit the RISE website for more details.

TWIST: Turbulence and Waves over Irregularly Sloping Topography

Fine- and microscale observations help us understand the interaction between internal waves and rough topography. Visit the TWIST website to find out more about internal tides and mixing on the corrugated continental slope off the east coast of the United States.

HOME: Hawaiian Ocean Mixing Experiment

The Absolute Velocity Profiler (AVP) and eXpendable Current Profilers (XCP) were used to characterize the internal waves radiating from the Hawaiian Ridge and estimate the associated dissipation (with Tom Sanford, Eric Kunze, and Craig Lee). Preliminary results can be found at the AVP HOME webpage.

Education

B.Sc., Queen's University at Kingston, Ont. (Engineering Physics), 1991
M.Sc., Cornell University (Environmental Engineering), 1995
Ph.D., Oregon State University (Physical Oceanography), May 2000

Publications

Seafloor pressure measurements of nonlinear internal waves, submitted to J. Phys. Oceanogr. (J.N. Moum and J.D. Nash)

Energy transport by nonlinear internal waves, in press, J. Phys. Oceanogr. (J.N. Moum, J.M. Klymak, J.D. Nash, A. Perlin and W.D. Smyth)

Hotspots of deep ocean mixing on the Oregon continental slope, Geophys. Res. Lett., 34, L01605, doi:10.1029/2006GL028170, 2007 (Nash, J. D., M. H. Alford, E. Kunze, K. Martini, and S. Kelly)

Structure of the baroclinic tide generated at Kaena Ridge, Hawaii, J. Phys. Oceanogr., 36(6), 1123-1135, 2006 (Nash, J.D., E. Kunze, C.M. Lee and T.B. Sanford)

An estimate of tidal energy lost to turbulence at the Hawaiian Ridge. J. Phys. Oceanogr., 36, 1148-1164, 2006. (Klymak, J.M., J.N. Moum, J.D. Nash, E. Kunze, J.B. Girton, G.S. Carter, C.M. Lee, T.B. Sanford, and M.C. Gregg)

Internal tides and turbulence along the 3000-m isobath of the Hawaiian Ridge, Journal of Physical Oceanography, 36(6), 1165-1183, 2006 (Lee, C.M., E. Kunze, T.B. Sanford, J.D. Nash, M.A. Merrifield, and P.E. Holloway) [pdf ]

River plumes as a source of large-amplitude internal waves in the coastal ocean, Nature, 437, 400-403, 2005 doi:10.1038/nature03936 (J.D. Nash and J.N. Moum)

Differential diffusion in breaking Kelvin-Helmholtz billows, J. Phys. Oceanogr., 35, 1004-1022, 2005. (W.D. Smyth, J.D. Nash and J.N. Moum)

Estimating Internal Wave Energy Fluxes in the Ocean, J. Atmos. and Oceanic Tech., 22(10), 1551-1570, 2005 (J.D. Nash, M.H. Alford and E. Kunze).

Internal tide reflection and turbulent mixing on the continental slope, Nash, J. Phys. Oceanogr. 34(5), 1117-1134, 2004 (J.D., E. Kunze, J. M. Toole and R. W. Schmitt)

An examination of the radiative and dissipative properties of deep ocean internal tides, Deep Sea Research II , 51 , 3029-3042, 2004 (St. Laurent, L. C. and J. D. Nash)

From tides to mixing along the Hawaiian Ridge, Science, 301, 355-357, 2003 (Experiment PIs including J.D. Nash)

Observations of boundary mixing over the continental slope, J. Phys. Oceanogr., 32, 2113-2130, 2002. (J.N. Moum, D.R. Caldwell, J.D. Nash and G.D. Gunderson)

Microstructure observations of turbulent salinity flux and the dissipation spectrum of salinity, J. Phys. Oceanogr., 2002, 32, 2312-2333 (J.D. Nash and J.N. Moum).

Internal hydraulic flows on the continental shelf: high drag states over a small bank, J. Geophys. Res., 106, 4593-4611, 2001 (J.D. Nash and J.N. Moum)

Topographically-induced drag and mixing at a small bank on the continental shelf, J. Phys. Oceanogr., 30, 2049-2054, 2000 (J.N. Moum and J.D. Nash)

Estimating salinity variance dissipation rate from microstructure conductivity measurements, J. Oceanic Atmos. Technol., 16, 263-274 , 1999 (J.D. Nash and J.N. Moum)

A thermocouple probe for high speed temperature measurements in the ocean, J. Oceanic Atmos. Technol., 16, 1474-1482, 1999 (J.D. Nash, D.R. Caldwell, M.J. Zelman and J.N. Moum)

Buoyant surface discharges into unsteady ambient flows, Dynamics of Atmospheres and Oceans. 24, 1-4, pp. 75, 1996 (J.D. Nash and G.H. Jirka)

Large scale Planar Laser Induced Fluorescence in turbulent density-stratified flows, Experiments in Fluids. Volume 19, Number 5, pp 297, 1995 (J.D. Nash, G.H. Jirka and D. Chen)