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Luc Rainville

Senior Oceanographer

Affiliate Assistant Professor, Oceanography

Email

rainville@apl.washington.edu

Phone

206-685-4058

Biosketch

Dr. Rainville's research interests reside primarily in observational physical oceanography and span the wide range of spatial and temporal scales in the ocean. From large-scale circulation to internal waves to turbulence, the projects he is involved in focus on the interactions between phenomena of different scales. He is motivated to find simple and innovative ways to study the ocean, primarily through sea-going oceanography but also using with remote sensing and modeling. In particular, Luc Rainville is interested in how phenomena typically considered 'small-scale' impact the oceanic system as a whole. * Propagation of internal waves through eddies and fronts. * Water mass formation and transformation by episodic forcing events. * Mixing and internal waves in the Arctic and in the Southern Ocean. Dr. Rainville joined the Ocean Physics Department at APL-UW at the end of 2007.

Department Affiliation

Ocean Physics

Education

B.Sc. Physics, McGill University, 1998

Ph.D. Oceanography, Scripps Institution of Oceanography, 2004

Projects

Marginal Ice Zone (MIZ) Program

An integrated program of observations and numerical simulations will focus on understanding ice–ocean–atmosphere dynamics in and around the MIZ, with particular emphasis on quantifying changes associated with decreasing ice cover. The MIZ measurement program will employ a novel mix of autonomous technologies (ice-based instrumentation, floats, drifters, and gliders) to characterize the processes that govern Beaufort Sea MIZ evolution from initial breakup and MIZ formation though the course of the summertime sea ice retreat.

22 Mar 2013

Tasmania Internal Tide Experiment

The Tasmanian continental slope will be instrumented with a range of tools including moored profiler, chi-pods, CTDs, and gliders to understand the process, strength, and distribution of ocean mixing from breaking internal waves.

27 Nov 2011

Internal Waves in Straits Experiment (IWISE)

With field work in the summers of 2010 and 2011, this project focuses on understanding the mechanisms controlling the generation of internal tides in the two-ridge system of Luzon Strait, along with their propagation, contribution to mixing (dissipation) and interaction with the Kuroshio.

27 Sep 2011

More Projects

Global Internal Tides from Altimetry

This collaborative project with Dr. Harper Simmons (U. Alaska), aims to construct a global map of low-mode internal tide energy flux and dissipation by application of state-of-the-art techniques to a combination of satellite altimetry, moorings, and a numerical model.

27 Sep 2011

Arctic Mixing: Changing Seasonality of Wind-driven Mixing

The Arctic Ocean, as we have come to know it over the last decades, is a quiescent, highly stratified ocean, with subsurface reservoirs and boundary sources of heat and nutrients that are often isolated from surface processes and the photic zone. The primary reason for this quiescence is believed to be the dominant presence of sea-ice, which acts to isolate the ocean from the mixing effects of wind. With the summer sea-ice reduction now exposing over 60% of the Arctic Ocean to the seasonal effects of wind forcing, it is urgent to consider the potential impacts of this available wind energy on the seasonality of the Arctic system. We suggest that the expanding extent and duration of seasonal open water in the Arctic has the potential to reshape the properties and stratification of the upper ocean, dramatically altering mixed layer depths, strengthening the internal wave field by at least an order of magnitude, thus enhancing turbulent mixing in the halo/pycnocline. If sufficiently strong, this enhanced mixing could bring nutrients and heat from the Pacific Waters into the surface and photic zone, with implications for Arctic ecosystems, surface fluxes, and feedbacks to sea-ice formation. In this collaborative proposal, we are using theory, observations and simple models to examine changes in Arctic mixed layer depths and internal wave energy and to predict impacts on Arctic ecosystems and the heat and freshwater balances of the Arctic.

 

Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES)

DIMES is a US/UK field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

 

Changes in Seasonality in the Arctic Ocean

The Arctic sea ice cover impedes the generation and damps the propagation of surface and internal waves. As more and more of the deep Arctic Ocean becomes ice-free in the summer, wind-driven inertial waves and mixing are likely to become increasingly important. This project studies the consequences of the decreasing ice cover on the stratification of the upper ocean as well as its impacts on the geochemistry and biological productivity of the Arctic system.

 

Salinity Processes in the Upper-Ocean Regional Study (SPURS)

In conjunction with the new Aquarius satellite mission, which will measure sea surface salinity from space, this project aims to directly measure an annual cycle of upper ocean salinity in the North Atlantic using by high-resolution glider surveys.

 

Publications

2000-present and while at APL-UW

Response of upper ocean currents to Typhoon Fanapi

Hormann, V., L.R. Centurioni, L. Rainville, C.M. Lee, and L.J. Braasch, "Response of upper ocean currents to Typhoon Fanapi," Geophys. Res. Lett, 41, 3995-4003, doi:10.1002/2014GL060317, 2014.

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16 Jun 2014

The response of upper ocean currents to Typhoon Fanapi in fall 2010 was studied using an extensive air-deployed drifter array. Separation of the observations into near-inertial and sub-inertial motions quantified the importance of strong advection by the sub-inertial circulation for the evolution of the cold wake formed by Typhoon Fanapi. The near-inertial currents generated during the storm showed the expected rightward bias, with peak magnitudes of up to 0.6 m/s and an e-folding time of about 4 days for the strong currents within the cold wake. The shear of the near-inertial currents is crucial for the storm-induced cooling and deepening of the mixed layer and such instabilities were here directly observed across the base of th — a dominant process for the wake warming — was found to be noticeably reduced when the near-inertial motions were strongest.

Variations of the North Pacific subtropical mode water from direct observations

Rainville, L., S.R. Jayne, and M.F. Cronin, "Variations of the North Pacific subtropical mode water from direct observations," J. Clim., 27, 2842-2860, doi:10.1175/JCLI-D-13-00227.1, 2014.

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1 Apr 2014

Mooring measurements from the Kuroshio Extension System Study (June 2004–June 2006) and from the ongoing Kuroshio Extension Observatory (June 2004–present) are combined with float measurements of the Argo network to study the variability of the North Pacific Subtropical Mode Water (STMW) across the entire gyre, on time scales from days, to seasons, to a decade. The top of the STMW follows a seasonal cycle, although observations reveal that it primarily varies in discrete steps associated with episodic wind events. The variations of the STMW bottom depth are tightly related to the sea surface height (SSH), reflecting mesoscale eddies and large-scale variations of the Kuroshio Extension and recirculation gyre systems. Using the observed relationship between SSH and STMW, gridded SSH products and in situ estimates from floats are used to construct weekly maps of STMW thickness, providing nonbiased estimates of STMW total volume, annual formation and erosion volumes, and seasonal and interannual variability for the past decade. Year-to-year variations are detected, particularly a significant decrease of STMW volume in 2007–10 primarily attributable to a smaller volume formed. Variability of the heat content in the mode water region is dominated by the seasonal cycle and mesoscale eddies; there is only a weak link to STMW on interannual time scales, and no long-term trends in heat content and STMW thickness between 2002 and 2011 are detected. Weak lagged correlations among air–sea fluxes, oceanic heat content, and STMW thickness are found when averaged over the northwestern Pacific recirculation gyre region.

Near-inertial internal wave field in the Canada basin from ice-tethered profilers

Dosser, H.V., L. Rainville, and J.M. Toole, "Near-inertial internal wave field in the Canada basin from ice-tethered profilers," J. Phys. Oceanogr., 44, 413-426, doi:10.1175/JPO-D-13-0117.1, 2014.

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1 Feb 2014

Salinity and temperature profiles from drifting ice-tethered profilers in the Beaufort gyre region of the Canada Basin are used to characterize and quantify the regional near-inertial internal wave field over one year. Vertical displacements of potential density surfaces from the surface to 750-m depth are tracked from fall 2006 to fall 2007. Because of the time resolution and irregular sampling of the ice-tethered profilers, near-inertial frequency signals are marginally resolved. Complex demodulation is used to determine variations with a time scale of several days in the amplitude and phase of waves at a specified near-inertial frequency. Characteristics and variability of the wave field over the course of the year are investigated quantitatively and related to changes in surface wind forcing and sea ice cover.

More Publications

Propagation of internal tides generated near Luzon Strait: Observations from autonomous gliders

Rainville, L., C.M. Lee, D.L. Rudnick, and K.-C. Yang, "Propagation of internal tides generated near Luzon Strait: Observations from autonomous gliders," J. Geophys. Res., 118, 4125-4138, doi:10.1002/jgrc.20293, 2013.

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1 Sep 2013

The vertical isopycnal displacements associated with internal waves generated by the barotropic tidal currents in the vicinity of Luzon Strait are estimated using measurements collected by autonomous underwater gliders. Nearly 23,000 profiles from Seagliders and Spray gliders, collected during 29 different missions since 2007, are used to estimate the amplitude and phase of the linear semidiurnal and diurnal internal waves in this energetic region, particularly in the previously poorly sampled area near the eastern ridge and on the Pacific side of Luzon Strait. The mean and variability of the internal wave field in the upper 1000 m of the water column are described. The phase progression of internal waves as they propagate away from their generation sites is captured directly. The glider-based observations are used to map the mode-1 semidiurnal and diurnal internal wave fields, providing the baroclinic energy flux over a roughly 600 km x 800 km region based strictly on in situ observations.

Observations of the cold wake of Typhoon Fanapi (2010)

Mrvaljevic, R.K., P.G. Black, L.R. Centurioni, Y.-T. Chang, E.A. D'Asaro, S.R. Jayne, C.M. Lee, R.-C. Lien, I.-I. Lin, J. Morzel, P.P. Niiler, L, Rainville, and T.B. Sanford, "Observations of the cold wake of Typhoon Fanapi (2010)," Geophys. Res. Lett., 40, 316-321, doi:10.1002/grl.50096, 2013.

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28 Jan 2013

Several tens of thousands of temperature profiles are used to investigate the thermal evolution of the cold wake of Typhoon Fanapi, 2010. Typhoon Fanapi formed a cold wake in the Western North Pacific Ocean on 18 September characterized by a mixed layer that was >2.5°C cooler than surrounding water, and extending to >80 m, twice as deep as the pre-existing mixed layer. The initial cold wake became capped after 4 days as a warm, thin surface layer formed. The thickness of the capped wake, defined as the 26°C to 27°C layer, decreased, approaching the background thickness of this layer with an e-folding time of 23 days, almost twice the e-folding lifetime of the Sea Surface Temperature (SST) cold wake (12 days). The wake was advected several hundreds of kilometers from the storm track by a pre-existing mesoscale eddy. The observations reveal new intricacies of cold wake evolution and demonstrate the challenges of describing the thermal structure of the upper ocean using sea surface information alone.

Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

Cronin, M.F., N.A. Bond, J.T. Farrar, H. Ichikawa, S.R. Jayne, Y. Kawai, M. Konda, B. Qiu, L. Rainville, and H. Tomita, "Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre," Deep-Sea Res. II, 85, 62-74, doi:10.1016/j.dsr2.2012.07.018, 2013.

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1 Jan 2013

Data from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the KE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3x10-4 m2/s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline.

Marginal Ice Zone (MIZ) Program: Science and Experiment Plan

Lee, C.M., et al., "Marginal Ice Zone (MIZ) Program: Science and Experiment Plan," APL-UW TR 1201, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, October 2012, 48 pp.

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9 Oct 2012

The Marginal Ice Zone (MIZ) intensive field program will employ an array of cutting-edge autonomous platforms to characterize the processes that govern Beaufort Sea MIZ evolution from initial breakup and MIZ formation though the course of the summertime sea ice retreat. Instruments will be deployed on and under the ice prior to initial formation of the MIZ along the Alaska coast, and will continue sampling from open water, across the MIZ, and into full ice cover, as the ice edge retreats northward through the summer. The flexible nature of ice-mounted and mobile, autonomous oceanographic platforms (e.g., gliders and floats) facilitates access to regions of both full ice cover and riskier MIZ regions. This approach exploits the extended endurance of modern autonomous platforms to maintain a persistent presence throughout the entire northward retreat. It also takes advantage of the inherent scalability of these instruments to sample over a broad range of spatial and temporal scales.

Mesoscale bio-physical interactions between the Agulhas Current and the Agulhas Bank, South Africa

Jackson, J.M., L. Rainville, M.J. Roberts, C.D. McQuaid, and J.R.E. Lutjeharms, "Mesoscale bio-physical interactions between the Agulhas Current and the Agulhas Bank, South Africa," Cont. Shelf. Res., 49, 10-24, doi:10.1016/j.csr.2012.09.005, 2012.

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1 Oct 2012

The Agulhas Current on the east coast of South Africa is a major western boundary current that exchanges heat and salt between the Indian and South Atlantic Oceans. The current retroflects as it deflects away from the African continent at the southern tip of the Agulhas Bank, a biologically productive extension of the continental shelf south of the South African coast. The less energetic Benguela Current borders the Agulhas Bank to the west. Little is known about mesoscale interactions between the Agulhas Current and the shelf waters of the Agulhas Bank or how these processes influence the biology of the bank. In this study, physical and biological data collected during a dedicated cruise in September 2010 allowed the identification of several mesoscale features that indicate a strong effect of the current on the bank, including a Natal Pulse that forced the Agulhas Current onto the Agulhas Bank. While on the bank itself, the current entrained particles that were then transported offshore. We also found evidence of upwelling on the southeast edge of the Agulhas Bank, which is thought to be a source of water for a cold ridge that characterizes the eastern region of the bank. Large fluctuations of the thermocline, consistent with internal waves, were observed inshore of the Agulhas Current, with high phytoplankton concentrations at their crests. We suggest that this is a physical effect, with doming of the waves concentrating plankton at their crests, thereby creating episodic biological hotspots.

Semi-diurnal baroclinic wave momentum fluxes at Kaena Ridge, Hawaii

Pinkel, R., L. Rainville, and J. Klymak, "Semi-diurnal baroclinic wave momentum fluxes at Kaena Ridge, Hawaii," J. Phys. Ocean., 42, 1249-1269, doi: 10.1175/JPO-D-11-0124.1, 2012.

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27 Apr 2012

Kaena Ridge, Hawaii is a site of energetic conversion of the semi-diurnal barotropic tide. Diffuse baroclinic wave beams emanate from the critical-slope regions near the ridge crest, directed upward and southward from the north flank of the ridge, upward and northward from the south flank. Here we attempt to quantify the momentum fluxes associated with generation at the Ridge. Continuous vertical profiles of density and velocity from 80–800 m were obtained from the Research Platform FLIP over the southern edge of the ridge, as an aspect of the Hawaii Ocean Mixing Experiment. Data are used to estimate the Reynolds stress, Eulerian buoyancy flux, and the combined Eliassen-Palm Flux in the semi-diurnal band. An upward-southward stress maximum of ~ 0.5 10-4 m2 s-2 appears at depths 300–500 m, generally consistent with beam-like behavior. A strong off-ridge buoyancy flux (~ 0.3 10-4 m2 s-3) combines with large along-ridge Reynolds stresses to form an Eliassen Palm flux whose along-ridge and across-ridge magnitudes are comparable. The stress azimuth rotates clockwise with increasing altitude above the ridge crest. The principal upward-southward beam is found to be at depths 100–300 m shallower than are predicted by an analytic 2-dimensional model and a 3-D numerical simulation. This discrepancy is consistent with previous observations of the baroclinic energy flux. If these observed tidal momentum fluxes were to diverge in a 100-m thick near-surface layer, the forcing would be comparable to a moderate wind stress. Pronounced lateral gradients of baroclinic tidal stresses can be expected offshore of Hawaiian topography.

Typhoon-ocean interaction in the western North Pacific: Part 1

D'Asaro, E., P. Black, L. Centurioni, P. Harr, S. Jayne, I.-I Lin, C. Lee, J. Morzel, R. Mrvaljevic, P.P. Niiler, L. Rainville, T. Sanford, and T.Y. Tang, "Typhoon-ocean interaction in the western North Pacific: Part 1," Oceanography, 24, 24-31, doi:10.5670/oceanog.2011.91, 2011

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5 Dec 2011

The application of new technologies has allowed oceanographers and meteorologists to study the ocean beneath typhoons in detail. Recent studies in the western Pacific Ocean reveal new insights into the influence of the ocean on typhoon intensity.

Energy flux and dissipation in Luzon Strait: Two tales of two ridges

Alford, M.H., J.A. MacKinnon, J.D. Nash, H. Simmons, A. Pickering, J.M. Klymak, R. Pinkel, O. Sun, L. Rainville, R. Musgrave, T. Beitzel, K.-H. Fu, and C.-W. Lu, "Energy flux and dissipation in Luzon Strait: Two tales of two ridges," J. Phys. Oceanogr., 41, 2211-2222, 2011.

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1 Nov 2011

Internal tide generation, propagation, and dissipation are investigated in Luzon Strait, a system of two quasi-parallel ridges situated between Taiwan and the Philippines. Two profiling moorings deployed for about 20 days and a set of nineteen 36-h lowered ADCP–CTD time series stations allowed separate measurement of diurnal and semidiurnal internal tide signals. Measurements were concentrated on a northern line, where the ridge spacing was approximately equal to the mode-1 wavelength for semidiurnal motions, and a southern line, where the spacing was approximately two-thirds that. The authors contrast the two sites to emphasize the potential importance of resonance between generation sites. Throughout Luzon Strait, baroclinic energy, energy fluxes, and turbulent dissipation were some of the strongest ever measured. Peak-to-peak baroclinic velocity and vertical displacements often exceeded 2 m s-1 and 300 m, respectively. Energy fluxes exceeding 60 kW m-1 were measured at spring tide at the western end of the southern line. On the northern line, where the western ridge generates appreciable eastward-moving signals, net energy flux between the ridges was much smaller, exhibiting a nearly standing wave pattern. Overturns tens to hundreds of meters high were observed at almost all stations. Associated dissipation was elevated in the bottom 500—1000 m but was strongest by far atop the western ridge on the northern line, where >500-m overturns resulted in dissipation exceeding 2 x 10-6 W kg-1 (implying diapycnal diffusivity K%u03C1 > 0.2 m2 s%u22121). Integrated dissipation at this location is comparable to conversion and flux divergence terms in the energy budget. The authors speculate that resonance between the two ridges may partly explain the energetic motions and heightened dissipation.

Impact of wind-driven mixing in the Arctic Ocean

Rainville, L., C.M. Lee, and R.A. Woodgate, "Impact of wind-driven mixing in the Arctic Ocean," Oceanography 24, 136-145, doi:10.5670/oceanog.2011.65, 2011.

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1 Sep 2011

The Arctic Ocean traditionally has been described as an ocean with low variability and weak turbulence levels. Many years of observations from ice camps and ice-based instruments have shown that the sea ice cover effectively isolates the water column from direct wind forcing and damps existing motions, resulting in relatively small upper-ocean variability and an internal wave field that is much weaker than at lower latitudes. Under the ice, direct and indirect estimates across the Arctic basins suggest that turbulent mixing does not play a significant role in the general distribution of oceanic properties and the evolution of Arctic water masses. However, during ice-free periods, the wind generates inertial motions and internal waves, and contributes to deepening of the mixed layer both on the shelves and over the deep basins - as at lower latitudes. Through their associated vertical mixing, these motions can alter the distribution of properties in the water column. With an increasing fraction of the Arctic Ocean becoming ice-free in summer and in fall, there is a crucial need for a better understanding of the impact of direct wind forcing on the Arctic Ocean.

Enhanced turbulence and energy dissipation at ocean fronts

D'Asaro, E., C. Lee, L. Rainville, L. Thomas, and R. Harcourt, "Enhanced turbulence and energy dissipation at ocean fronts," Science, 332, 318-322, doi:0.1126/science.1201515, 2011.

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15 Apr 2011

The ocean surface boundary layer mediates air-sea exchange. In the classical paradigm and in current climate models, its turbulence is driven by atmospheric forcing. Observations at a 1-km-wide front within the Kuroshio found the rate of energy dissipation within the boundary layer to be enhanced by 10 to 20 times, suggesting that the front not the atmospheric forcing supplied the energy for the turbulence. The data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence. The resulting boundary layer is stratified, in contrast to the classically well-mixed layer. These effects will be strongest at the intense fronts found in the Kuroshio, Gulf Stream, and Antarctic Circumpolar Current, key players in the climate system.

Distribution of deep near-inertial waves observed in the Kuroshio Extension

Park, J.-H., K.A. Donohue, D.R. Watts, and L. Rainville, "Distribution of deep near-inertial waves observed in the Kuroshio Extension," J. Oceanogr., 66, 709-717, doi:10.1007/s10872-010-0058-0, 2010.

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1 Oct 2010

The distribution of deep near-inertial waves (NIWs) is investigated using data mainly from an array of 46 near-bottom acoustic current meter sensors spanning a 600 km x 600 km region as part of the Kuroshio Extension System Study during 2004–2006. The deep NIW distribution is interpreted in the context of both upper-layer and near-bottom mapped circulations. The wintertime-mean mixed-layer NIW energy input, modeled from observed wind stress, has the same range of values north and south of the Kuroshio Extension in this region. Yet, the wintertime-mean deep NIW energy distribution reveals a sharp factor-of-5 decrease from north to south of the Kuroshio jet. This direct observational evidence shows that the Kuroshio Extension blocks the equatorward propagation of NIWs. The NIW energy that does reach the sea floor within the subset of wintertime observations in the subtropical gyre arrives with patchy spatial and temporal distribution. Elevated NIW energy in deep water is associated with anticyclones in the deep barotropic flow and unassociated with upper layer eddies.

Interference pattern and propagation of the M2 internal tide south of the Hawaiian Ridge

Rainville, L., T.M.S. Johnston, G.S. Carter, M.A. Merrifield, R. Pinkel, P.F. Worcester, and B.D. Dushaw, "Interference pattern and propagation of the M2 internal tide south of the Hawaiian Ridge," J. Phys. Oceanogr., 40, 311-325, 2010.

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1 Feb 2010

Most of the M2 internal tide energy generated at the Hawaiian Ridge radiates away in modes 1 and 2, but direct observation of these propagating waves is complicated by the complexity of the bathymetry at the generation region and by the presence of interference patterns.

Observations from satellite altimetry, a tomographic array, and the R/P FLIP taken during the Farfield Program of the Hawaiian Ocean Mixing Experiment (HOME) are found to be in good agreement with the output of a high-resolution primitive equation model, simulating the generation and propagation of internal tides. The model shows that different modes are generated with different amplitudes along complex topography. Multiple sources produce internal tides that sum constructively and destructively as they propagate. The major generation sites can be identified using a simplified 2D idealized knife-edge ridge model. Four line sources located on the Hawaiian Ridge reproduce the interference pattern of sea surface height and energy flux density fields from the numerical model for modes 1 and 2. Waves from multiple sources and their interference pattern have to be taken into account to correctly interpret in situ observations and satellite altimetry.

Observations of internal wave generation in the seasonally ice-free Arctic

Rainville, L., and R.A. Woodgate, "Observations of internal wave generation in the seasonally ice-free Arctic," Geophys. Res. Lett., 36, 10.1029/2009GL041291, 2009.

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2 Dec 2009

The Arctic is generally considered a low energy ocean. Using mooring data from the northern Chukchi Sea, we confirm that this is mainly because of sea-ice impeding input of wind energy into the ocean. When sea-ice is present, even strong storms do not induce significant oceanic response. However, during ice-free seasons, local storms drive strong inertial currents (>20 cm/s) that propagate throughout the water column and significantly deepen the surface mixed layer. The large vertical shear associated with summer inertial motions suggests a dominant role for localized and seasonal vertical mixing in Arctic Ocean dynamics. Our results imply that recent extensive summer sea-ice retreat will lead to significantly increased internal wave generation especially over the shelves and also possibly over deep waters. This internal wave activity will likely dramatically increase upper-layer mixing in large areas of the previously quiescent Arctic, with important ramifications for ecosystems and ocean dynamics.

The Kuroshio Extension and its recirculation gyre

Jayne, S.R. et al., including L. Rainville, "The Kuroshio Extension and its recirculation gyre," Deep-Sea Res. I, 56, 2088-2099, doi:10.1016/j.dsr.2009.08.006, 2009.

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1 Dec 2009

This paper reports on the strength and structure of the Kuroshio Extension and its recirculation gyres. In the time average, quasi-permanent recirculation gyres are found to the north and south of the Kuroshio Extension jet. The characteristics of these recirculations gyres are determined from the combined observations from the Kuroshio Extension System Study (KESS) field program (June 2004–June 2006) and include current meters, pressure and current recording inverted echo sounders, and subsurface floats. The position and strength of the recirculation gyres simulated by a high-resolution numerical model are found to be consistent with the observations. The circulation pattern that is revealed is of a complex system of multiple recirculation gyres that are embedded in the crests and troughs of the quasi-permanent meanders of the Kuroshio Extension. At the location of the KESS array, the Kuroshio Extension jet and its recirculation gyres transport of about 114 Sv. This represents a 2.7-fold increase in the transport of the current compared to the Kuroshio's transport at Cape Ashizuri before it separates from the coast and flows eastward into the open ocean. This enhancement in the current's transport comes from the development of the flanking recirculation gyres. Estimates from an array of inverted echo sounders and a high-resolution ocean general circulation model are of similar magnitude.

Mixing across the Arctic Ocean: Microstructure observations during the Beringia 2005 Expedition

Rainville, L., and P. Winsor, "Mixing across the Arctic Ocean: Microstructure observations during the Beringia 2005 Expedition," Geophys. Res. Lett., 35, doi:10.1029/2008GL033532, 2008.

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30 Apr 2008

Turbulent-scale temperature and conductivity were measured during the pan-arctic Beringia 2005 Expedition. The rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from Alaska to the North Pole, across deep flat basins (Canada and Makarov Basins) and steep ridges (Alpha-Mendeleev and Lomonosov Ridges). The mixing rates are observed to be small relative to lower latitudes but also remarkably non-uniform. Relatively elevated turbulence is found over deep topography, confirming the dominant role of bottom-generated internal waves. Measured patterns of mixing in the Arctic are also associated with other mechanisms, such as double-diffusive structures and deep overflows. A better knowledge of the distribution of mixing is essential to understand the dynamics of the changing Arctic environment.

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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