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Tom Sanford

Senior Principal Oceanographer Emeritus

Professor Emeritus, Oceanography

Email

sanford@apl.washington.edu

Phone

206-543-1365

Research Interests

Physical Oceanography; Instrumentation; Structure and Dynamics of Currents, Eddies and Waves; Propagation and Dissipation of Internal Waves

Biosketch

Dr. Sanford conducts innovative, high-quality basic and applied oceanographic research, teaches graduate students, mentors postdoctoral researchers, and fosters collaborations with national and international investigators and organizations. Broadly, his research exploits motional induction theory — the motion of seawater through the Earth's magnetic field that produces electric currents and magnetic fields — to infer important aspects of ocean properties and kinetic structure. These methods have been applied to a range of studies in the open ocean and within channels. In nearly five decades as an experimental physical oceanographer, Sanford has participated in many dozen cruises and research projects, provided the oceanographic community with important results, and developed several instruments and new observational methods. Recent efforts include the development of two ocean velocity sensors, one an autonomous vertical profiler (EM-APEX) and the other a bottom lander (HPIES). Prior to these, he led the development of the XCP, an expendable current profile. These are being used to study upper-ocean mixing and convective processes, interactions between internal waves and steady currents, momentum flux into the ocean (such as from hurricanes), as well as the structure and variability of oceanic boundary and estuarine currents.

As Professor in the UW School of Oceanography, Dr. Sanford has taught courses and advised advanced research for about two-dozen graduate students and postdocs. Dr. Sanford is a Fellow of the American Geophysical Union and American Meteorological Society, received the IEEE/Ocean Engineering Society 2008 Distinguished Technical Achievement Award and in 2010 the AMS Henry Stommel Research Award. Since 2008 he has served as an ONR Secretary of the Navy/Chief of Naval Operations Chair of Oceanographic Sciences.

Department Affiliation

Ocean Physics

Education

A.B. Physics, Oberlin College, 1962

Ph.D. Physical Oceanography, Massachusetts Institute of Technology, 1967

Projects

Origins of the Kuroshio and Mindanao Currents

The boundary currents off the east coast of the Philippines are of critical importance to the general circulation of the Pacific Ocean. The westward flowing North Equatorial Current (NEC) runs into the Philippine coast and bifurcates into the northward Kuroshio and the southward Mindanao Current. Quantifying these flows and understanding bifurcation dynamics are essential to improving predictions of regional circulation and Pacific Ocean climate. We have deployed five HPIES off NE Luzon Island under the Kuroshio and nine EM-APEX floats in the NEC as it flows westward toward the Philippine Islands.

8 May 2013

Lateral Mixing

Small scale eddies and internal waves in the ocean mix water masses laterally, as well as vertically. This multi-investigator project aims to study the physics of this mixing by combining dye dispersion studies with detailed measurements of the velocity, temperature and salinity field during field experiments in 2011 and 2012.

1 Sep 2012

Publications

2000-present and while at APL-UW

Small-scale potential vorticity in the upper-ocean thermocline

Lien, R.-C., and T.B. Sanford, "Small-scale potential vorticity in the upper-ocean thermocline," J. Phys. Oceangr., 49, 1845-1872, doi:10.1175/JPO-D-18-0052.1, 2019.

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1 Jul 2019

Twenty Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper-ocean thermocline of the summer Sargasso Sea observed the temporal and vertical variations of Ertel potential vorticity (PV) at 7–70-m vertical scale, averaged over O(4–8)-km horizontal scale. PV is dominated by its linear components — vertical vorticity and vortex stretching, each with an rms value of ~0.15f. In the internal wave frequency band, they are coherent and in phase, as expected for linear internal waves. Packets of strong, >0.2f, vertical vorticity and vortex stretching balance closely with a small net rms PV. The PV spectrum peaks at the highest resolvable vertical wavenumber, ~0.1 cpm. The PV frequency spectrum has a red spectral shape, a –1 spectral slope in the internal wave frequency band, and a small peak at the inertial frequency. PV measured at near-inertial frequencies is partially attributed to the non-Lagrangian nature of float measurements. Measurement errors and the vortical mode also contribute to PV in the internal wave frequency band. The vortical mode Burger number, computed using time rates of change of vertical vorticity and vortex stretching, is 0.2–0.4, implying a horizontal kinetic energy to available potential energy ratio of ~0.1. The vortical mode energy frequency spectrum is 1–2 decades less than the observed energy spectrum. Vortical mode energy is likely underestimated because its energy at vertical scales > 70 m was not measured. The vortical mode to total energy ratio increases with vertical wavenumber, implying its importance at small vertical scales.

Scaling of drag coefficients under five tropical cyclones

Hsu, J.-Y., R.-C. Lien, E.A. D'Asaro, and T.B. Sanford, "Scaling of drag coefficients under five tropical cyclones," Geophys. Res. Lett., EOR, doi:10.1029/2018GL081574, 2019.

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4 Mar 2019

The forecast of tropical cyclone intensification is critical to the protection of coastlines, involving the complicated tropical cyclone‐ocean interaction. The wind of storms can force strong near‐inertial current via surface wind stress (often parameterized by a drag coefficient Cd), and then induce the upper ocean cooling due to the shear instability. The transferred momentum and reduced heat supply can both restrict tropical cyclones' development. In other words, the Cd can affect the prediction of momentum and thermal response under storms, and thereby the forecast on storm intensity. This study investigates the spatial variability of downwind drag coefficient Cd under five different tropical cyclones, by integrating the storm‐induced ocean momentum because previous results of Cd as a function of wind speed |U10| are scattered significantly at |U10|= 25–40 m/s. Here, larger Cd in the front‐right sector of faster storms than that of slower stoms is found, presumably due to the surface wave effect. A new parameterization of Cd using the surface wave properties under tropical cyclones is proposed, which largely improves the conventional parameterization of Cd(|U10|). Future studies on the tropical cyclone‐wave‐ocean interaction and storm intensification forecast will be benefited from this new parameterization.

Estimates of surface waves using subsurface EM-APEX floats under Typhoon Fanapi 2010

Hsu, J.-Y., R.-C. Lien, E.A. D'Asaro, T.B. Sanford, "Estimates of surface waves using subsurface EM-APEX floats under Typhoon Fanapi 2010," J. Atmos. Ocean. Technol., 35, 1053-1075, doi:10.1175/JTECH-D-17-0121.1, 2018.

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1 May 2018

Seven subsurface Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats measured the voltage induced by the motional induction of seawater under Typhoon Fanapi in 2010. Measurements were processed to estimate high-frequency oceanic velocity variance associated with surface waves. Surface wave peak frequency fp and significant wave height Hs are estimated by a nonlinear least squares fitting to oceanic velocity, assuming a broadband JONSWAP surface wave spectrum. The Hs is further corrected for the effects of float rotation, Earth's geomagnetic field inclination, and surface wave propagation direction. The fp is 0.08–0.10 Hz, with the maximum fp of 0.10 Hz in the rear-left quadrant of Fanapi, which is ~0.02 Hz higher than in the rear-right quadrant. The Hs is 6–12 m, with the maximum in the rear sector of Fanapi. Comparing the estimated fp and Hs with those assuming a single dominant surface wave yields differences of more than 0.02 Hz and 4 m, respectively. The surface waves under Fanapi simulated in the WAVEWATCH III (ww3) model are used to assess and compare to float estimates. Differences in the surface wave spectra of JONSWAP and ww3 yield uncertainties of <5% outside Fanapi’s eyewall and >10% within the eyewall. The estimated fp is 10% less than the simulated ww3 peak wave frequencey before the passage of Fanapi’s eye and 20% less after eye passage. Most differences between Hs and simulated ww3 significant wave height are <2 m except those in the rear-left quadrant of Fanapi, which are ~5 m. Surface wave estimates are important for guiding future model studies of tropical cyclone wave–ocean interactions.

More Publications

Inventions

Remote Sensing of Salinity Profiles in a Marine Estuary

Record of Invention Number: 47312

Tom Sanford, Jim Carlson, John Dunlap

Disclosure

22 Apr 2015

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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