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Andrey Shcherbina

Principal Oceanographer

Affiliate Assistant Professor, Civil and Environmental Engineering

Email

ashcherbina@apl.washington.edu

Phone

206-897-1446

Department Affiliation

Ocean Physics

Education

M.S. Physical Oceanography, Moscow Institute of Physics and Technology, 1998

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

Andrey Shcherbina's Website

http://faculty.washington.edu/shcher/

Projects

Salinity Processes in the Upper Ocean Regional Study — SPURS

The NASA SPURS research effort is actively addressing the essential role of the ocean in the global water cycle by measuring salinity and accumulating other data to improve our basic understanding of the ocean's water cycle and its ties to climate.

15 Apr 2015

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

APL-UW Involvement in the Coastal Margin Observation and Prediction Science and Technology Center (CMOP)

AUVs will be deployed by a newly formed APL-UW AUV group as part of CMOP's experimental observation network which consists of multiple fixed and mobile platforms equipped with oceanographic sensors.

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15 Jun 2012

The Center for Coastal Margin Observation and Predication (CMOP) has purchased from Hydroid, LLC two Autonomous Underwater Vehicles (AUVs) for its studies. The REMUS (Remote Environmental Measuring Units) 100 (see Figure 1) is a compact, light-weight, AUV designed for operation in coastal environments up to 100 meters in depth. The AUVs will be deployed by a newly formed APL-UW AUV group as part of CMOP's experimental observation network which consists of multiple fixed and mobile platforms equipped with oceanographic sensors. The AUVs will be used, primarily, to study the Columbia River plume and estuary region. The AUVs will be deployed periodically throughout each operational year. We also plan to allow customization of the AUVs by integrating novel biogeochemical sensors to meet specific scientific objectives for the CMOP program.

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Publications

2000-present and while at APL-UW

Model-aided Lagrangian interpretation of non-synoptic estuarine observations

Shcherbina, A.Y., C.L. McNeil, and A.M. Baptista, "Model-aided Lagrangian interpretation of non-synoptic estuarine observations," Limnol. Oceanogr. Method., 14, 397-407, doi:10.1002/lom3.10098, 2016.

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1 Jun 2016

We propose a novel method for constructing a pseudo-synoptic view of estuarine features from non-synoptic observations captured by mobile platforms. The model-aided Lagrangian interpretation (MALI) method is based on relocating observations to a common reference moment in time along three-dimensional Lagrangian trajectories derived from a numerical model of estuarine circulation. The method relies on the model skill to capture large-scale circulation features, and on high-resolution in situ observations to characterize small-scale hydrographic structure. We demonstrate our technique by applying MALI to autonomous underwater vehicle observations in the Columbia River estuary, with the aid of a validated unstructured-grid finite-element numerical simulation. The method can be readily adapted to a broader range of environments, observational platforms, and model-data combinations.

Submesoscale streamers exchange water on the north wall of the Gulf Stream

Klymak, J.M., R.K. Shearman, J. Gula, C.M. Lee, E.A. D'Asaro, L.N. Thomas, R.R. Harcourt, A.Y. Shcherbina, M.A. Sundermeyer, J. Molemaker, and J.C. McWilliams, "Submesoscale streamers exchange water on the north wall of the Gulf Stream," Geophys. Res. Lett., 43, 1226-1233, doi:10.1002/2015GL067152, 2016.

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16 Feb 2016

The Gulf Stream is a major conduit of warm surface water from the tropics to the subpolar North Atlantic. Here we observe and simulate a submesoscale (<20 km) mechanism by which the Gulf Stream exchanges water with subpolar water to the north. Along isopycnals, the front has a sharp compensated temperature-salinity contrast, with distinct mixed water between the two water masses 2 and 4 km wide. This mixed water does not increase downstream despite substantial energy available for mixing. A series of streamers detrain this water at the crest of meanders. Subpolar water replaces the mixed water and resharpens the front. The water mass exchange accounts for a northward flux of salt of 0.5–2.5 psu m2 s-1, (large-scale diffusivity O (100 m2 s-1)). This is similar to bulk-scale flux estimates of 1.2 psu m2 s-1 and supplies fresher water to the Gulf Stream required for the production of 18° subtropical mode water.

Symmetric instability, inertial oscillations, and turbulence at the Gulf Stream front

Thomas, L.N., J.R. Taylor, E.A. D'Asaro, C.M. Lee, J.M. Klymak, and A. Shcherbina, "Symmetric instability, inertial oscillations, and turbulence at the Gulf Stream front," J. Phys. Oceanogr., 46, 197-217, doi:10.1175/JPO-D-15-0008.1, 2016.

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1 Jan 2016

The passage of a winter storm over the Gulf Stream observed with a Lagrangian float and hydrographic and velocity surveys provided a unique opportunity to study how the interaction of inertial oscillations, the front, and symmetric instability (SI) shapes the stratification, shear, and turbulence in the upper ocean under unsteady forcing. During the storm, the rapid rise and rotation of the winds excited inertial motions. Acting on the front, these sheared motions modulate the stratification in the surface boundary layer. At the same time, cooling and downfront winds generated a symmetrically unstable flow. The observed turbulent kinetic energy dissipation exceeded what could be attributed to atmospheric forcing, implying SI drew energy from the front. The peak excess dissipation, which occurred just prior to a minimum in stratification, surpassed that predicted for steady SI turbulence, suggesting the importance of unsteady dynamics. The measurements are interpreted using a large-eddy simulation (LES) and a stability analysis configured with parameters taken from the observations. The stability analysis illustrates how SI more efficiently extracts energy from a front via shear production during periods when inertial motions reduce stratification. Diagnostics of the energetics of SI from the LES highlight the temporal variability in shear production but also demonstrate that the time-averaged energy balance is consistent with a theoretical scaling that has previously been tested only for steady forcing. As the storm passed and the winds and cooling subsided, the boundary layer restratified and the thermal wind balance was reestablished in a manner reminiscent of geostrophic adjustment.

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The LatMix summer campaign: Submesoscale stirring in the upper ocean

Shcherbina, A.Y., et al., including E. D'Asaro, R.R. Harcourt, C.M. Lee, R.-C. Lien, and T.B. Sanford, "The LatMix summer campaign: Submesoscale stirring in the upper ocean," Bull. Am. Meteor. Soc., 96, 1257-1279, doi:10.1175/BAMS-D-14-00015.1, 2015.

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1 Aug 2015

Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s-1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.

Variability and interleaving of upper-ocean water masses surrounding the North Atlantic salinity maximum

Shcherbina, A.Y., E.A. D'Asaro, S.C. Riser, and W.S. Kessler, "Variability and interleaving of upper-ocean water masses surrounding the North Atlantic salinity maximum," Oceanography, 28, 106-113, doi:10.5670/oceanog.2015.12, 2015.

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1 Mar 2015

The North Atlantic subtropical salinity maximum harbors the saltiest surface waters of the open world ocean. Subduction of these waters gives rise to Subtropical Underwater, spreading the high-salinity signature over the entire basin. The Salinity Processes in the Upper-ocean Regional Study (SPURS) is aimed at understanding the physics controlling the thermohaline structure in the salinity maximum region. A combination of moored and autonomous float observations is used here to describe the vertical water mass interleaving in the area. Seasonal intensification of interleaving in late spring and the abundance of small-scale thermohaline intrusions point to an important role for submesoscale processes in the initial subduction and subsequent evolution of Subtropical Underwater.

Variability in near-surface salinity from hours to decades in the eastern North Atlantic: The SPURS region

Riser, S.C., J. Anderson, A. Shcherbina, and E.D'Asaro, "Variability in near-surface salinity from hours to decades in the eastern North Atlantic: The SPURS region," Oceanography, 28, 66-77, doi:10.5670/oceanog.2015.11, 2015.

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1 Mar 2015

We examine the variability of near-surface salinity in a 10° x 10° region of the eastern North Atlantic, the location of the first part of the Salinity Processes in the Upper-ocean Regional Study (SPURS-1). The data used were collected over a two-year period, largely by a group of two types of profiling floats equipped with sensors that record high-resolution temperature and salinity measurements in the upper few meters of the water column. By comparing the SPURS-1 measurements to observations in the area from previous decades, we examine variability at time scales ranging from a few hours (mostly consisting of rainfall-driven decreases in salinity) to diurnal cycles in temperature and salinity, seasonal variability and the annual cycle, and finally to decadal-scale changes. The relationship of near-surface salinity to the hydrological cycle suggests a continuous spectrum of variability in this cycle from hours to decades.

Quantifying upper ocean turbulence driven by surface waves

D'Asaro, E.A., J. Thomson, A.Y. Shcherbina, R.R. Harcourt, M.F. Cronin, M.A. Hemer, and B. Fox-Kemper, "Quantifying upper ocean turbulence driven by surface waves," Geophys. Res. Lett, 41, 102-107, doi:10.1002/1013GL058193, 2014.

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1 Jan 2014

Nearly all operational ocean models use air-sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates. This approach implicitly parameterizes surface wave effects in terms of these inputs. Here, we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves. Under the same wind stress and adjusting for buoyancy flux, we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake. The increase is consistent with models of Langmuir turbulence, in which the wave Stokes drift, and not wave breaking, is the dominant mechanism by which waves energize turbulence in the mixed layer. Applying these same theories globally, we find enhanced mixing and deeper mixed layers resulting from the inclusion of Langmuir turbulence in the boundary layer parameterization, especially in the Southern Ocean.

Waves and the equilibrium range at Ocean Weather Station P

Thomson, J., E.A. D'Asaro, M.F. Cronin, W.E. Rogers, R.R. Harcourt, and A. Shcherbina, "Waves and the equilibrium range at Ocean Weather Station P," J. Geophys. Res., 118, 5951-5962, doi:10.1002/2013JC008837, 2013.

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1 Nov 2013

Wave and wind measurements at Ocean Weather Station P (OWS-P, 50°N 145°W) are used to evaluate the equilibrium range of surface wave energy spectra. Observations are consistent with a local balance between wind input and breaking dissipation, as described by Philips (1985). The measurements include direct covariance wind stress estimates and wave breaking dissipation rate estimates during a 3 week research cruise to OWS-P. The analysis is extended to a wider range of conditions using observations of wave energy spectra and wind speed during a 2 year mooring deployment at OWS-P. At moderate wind speeds (5–15 m/s), mooring wave spectra are in agreement, within 5% uncertainty, with the forcing implied by standard drag laws and mooring wind measurements. At high wind speeds (>15 m/s), mooring wave spectra are biased low, by 13%, relative to the forcing implied by standard drag laws and mooring wind measurements. Deviations from equilibrium are associated with directionality and variations at the swell frequencies. A spectral wave hindcast accurately reproduces the mooring observations, and is used to examine the wind input.

Statistics of vertical vorticity, divergence, and strain in a developed submesoscale turbulence field

Shcherbina, A.Y., E.A. D'Asaro, C.M. Lee, J.M. Klymak, M.J. Molemaker, and J.C. McWilliams, "Statistics of vertical vorticity, divergence, and strain in a developed submesoscale turbulence field," Geophys. Res. Lett., 40, 4706-4711, doi:10.1002/grl.50919, 2013.

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16 Sep 2013

A detailed view of upper ocean vorticity, divergence, and strain statistics was obtained by a two-vessel survey in the North Atlantic Mode Water region in winter 2012. Synchronous Acoustic Doppler Current Profiler sampling provided the first in situ estimates of the full velocity gradient tensor at O(1 km) scale without the usual mix of spatial and temporal aliasing. The observed vorticity distribution in the mixed layer was markedly asymmetric (skewness 2.5), with sparse strands of strong cyclonic vorticity embedded in a weak, predominantly anticyclonic background. Skewness of the vorticity distribution decreased linearly with depth, disappearing completely in the pycnocline. Statistics of divergence and strain rate generally followed the normal and χ distributions, respectively. These observations confirm a high-resolution numerical model prediction for the structure of the active submesoscale turbulence field in this area.

Observations of near-inertial internal gravity waves radiating from a frontal jet

Alford, M.H., A.Y. Shcherbina, and M.C. Gregg, "Observations of near-inertial internal gravity waves radiating from a frontal jet," J. Phys. Oceanogr., 43, 1225-1239, doi:10.1175/JPO-D-12-0146.1, 2013.

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1 Jun 2013

Shipboard ADCP and towed CTD measurements are presented of a near-inertial internal gravity wave radiating away from a zonal jet associated with the Subtropical Front in the North Pacific. Three-dimensional spatial surveys indicate persistent alternating shear layers sloping downward and equatorward from the front. As a result, depth-integrated ageostrophic shear increases sharply equatorward of the front. The layers have a vertical wavelength of about 250 m and a slope consistent with a wave of frequency 1.01 f. They extend at least 100 km south of the front. Time series confirm that the shear is associated with a downward-propagating near-inertial wave with frequency within 20% of f. A slab mixed layer model forced with shipboard and NCEP reanalysis winds suggests that wind forcing was too weak to generate the wave. Likewise, trapping of the near-inertial motions at the low-vorticity edge of the front can be ruled out because of the extension of the features well south of it. Instead, the authors suggest that the wave arises from an adjustment process of the frontal flow, which has a Rossby number about 0.2–0.3.

Offshore transport of shelf waters through interaction of vortices with a shelfbreak current

Cenedese, C., R.E. Todd, G.G. Gawarkiewicz, W. Brechner Owens, and A.Y. Shcherbina, "Offshore transport of shelf waters through interaction of vortices with a shelfbreak current," J. Phys. Oceanogr., 45, 905-919, doi:10.1175/JPO-D-12-0150.1, 2013.

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1 May 2013

Interactions between vortices and a shelfbreak current are investigated, with particular attention to the exchange of waters between the continental shelf and slope. The nonlinear, three-dimensional interaction between an anticyclonic vortex and the shelfbreak current is studied in the laboratory while varying the ratio ε of the maximum azimuthal velocity in the vortex to the maximum alongshelf velocity in the shelfbreak current. Strong interactions between the shelfbreak current and the vortex are observed when ε > 1; weak interactions are found when ε < 1. When the anticyclonic vortex comes in contact with the shelfbreak front during a strong interaction, a streamer of shelf water is drawn offshore and wraps anticyclonically around the vortex. Measurements of the offshore transport and identification of the particle trajectories in the shelfbreak current drawn offshore from the vortex allow quantification of the fraction of the shelfbreak current that is deflected onto the slope; this fraction increases for increasing values of ε. Experimental results in the laboratory are strikingly similar to results obtained from observations in the Middle Atlantic Bight (MAB); after proper scaling, measurements of offshore transport and offshore displacement of shelf water for vortices in the MAB that span a range of values of ε agree well with laboratory predictions.

Chlorophyll bloom development and the subtropical front in the North Pacific

Wilson, C., T.A. Villareal, M.A. Brzezinski, J.W. Krause, and A.Y. Shcherbina, "Chlorophyll bloom development and the subtropical front in the North Pacific," J. Geophys. Res., 118, 1473-1488, doi:10.1002/jgrc.20143, 2013.

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1 Mar 2013

In late summer, satellite ocean color data consistently show localized chlorophyll blooms in the oligotrophic NE Pacific. Based on historical data and the results from recent cruises, these blooms are associated with elevated diatom abundance. However, the physical dynamics that stimulate the blooms remain unknown. Mechanisms suggested to be driving the blooms include mixing at the subtropical front, breaking of internal waves at the critical latitude, shoaling of the mixed layer depth, eddy interactions, and winter mixing of nutrients. To examine these hypotheses, we use data from four summer cruises (2002, 2007, 2008, and 2009) in this region that sampled near a bloom temporally and/or spatially. Conditions associated with five blooms (two blooms were sampled in 2009) are examined. Each area was sampled at a different stage in bloom development, including prebloom, initiation, full bloom, decline, and postbloom conditions. No one variable is found which can explain unequivocally the development of a chlorophyll bloom at a certain location. We describe a set of conditions that could result in the injection of nutrients into the surface water to stimulate a bloom. This "perfect storm" of conditions requires a subsurface stratification minimum layer that intersects the nutricline and that this minimum is close to the base of the mixed layer. These conditions are not predictable in the sense of an annual climatology; however, they do occur often enough to create a reasonably certain, if spatially variable, summer NE Pacific bloom.

Three-dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the North Pacific subtropical frontal zone

Shcherbina, A.Y., M.C. Gregg, M.H. Alford, M.H., and R.R. Harcourt, "Three-dimensional structure and temporal evolution of submesoscale thermohaline intrusions in the North Pacific subtropical frontal zone," J. Phys. Oceanogr., 40, 1669-1689, doi:10.1175/2010JPO4373.1, 2010.

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1 Aug 2010

Four instances of persistent intrusive deformation of the North Pacific Subtropical Front were tagged individually by a Lagrangian float and tracked for several days. Each feature was mapped in three dimensions using repeat towed observations referenced to the float. Isohaline surface deformations in the frontal zone included sheetlike folds elongated in the alongfront direction and narrow tongues extending across the front. All deformations appeared as protrusions of relatively cold, and fresh, water across the front. No corresponding features of the opposite sign or isolated lenslike structures were observed. The sheets were O(10 m) thick, protruded about 10 km into the warm saline side of the front, and were coherent for 10–30 km along the front. Having about the same thickness and cross-frontal extent as the sheets, tongues extended less than 5 km along the front.

All of the intrusions persisted as long as they were followed, several days to one week. Their structures evolved on both inertial (23 h) and subinertial (10 days) time scales in response to differential lateral advection. The water mass surrounding the intrusions participated in gradual anticyclonic rotation as a part of a mesoscale meander of the subtropical front. The intrusions may be interpreted as a manifestation of three-dimensional submesoscale turbulence of the frontal zone, driven by the mesoscale. Absence of large features of the opposite sign may be indicative of the asymmetry of the underlying dynamics.

Characterizing thermohaline intrusions in the North Pacific subtropical frontal zone

Shcherbina, A.Y., M.C. Gregg, M.H. Alford, and R.R. Harcourt, "Characterizing thermohaline intrusions in the North Pacific subtropical frontal zone," J. Phys. Oceanogr., 39, 2735-2756, 2009.

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1 Nov 2009

A monthlong field survey in July 2007, focused on the North Pacific subtropical frontal zone (STFZ) near 30°N, 158°W, combined towed depth-cycling conductivity-temperature-depth (CTD) profiling with shipboard current observations. Measurements were used to investigate the distribution and structure of thermohaline intrusions. The study revealed that local extrema of vertical salinity profiles, often used as intrusion indicators, were only a subset of a wider class of distortions in thermohaline fields due to interleaving processes. A new method to investigate interleaving based on diapycnal spiciness curvature was used to describe an expanded class of laterally coherent intrusions. STFZ intrusions were characterized by their overall statistics and by a number of case studies. Thermohaline interleaving was particularly intense within 5 km of two partially compensated fronts, where intrusions with both positive and negative salinity anomalies were widespread. The vertical and cross-frontal scales of the intrusions were on the order of 10 m and 5 km, respectively. Though highly variable, the slopes of these features were typically intermediate between those of isopycnals and isohalines. Although the influence of double-diffusive processes sometime during the evolution of intrusions could not be excluded, the broad spectrum of the observed features suggests that any role of double diffusion was secondary.

Inventions

Open Water Detection from Beneath Sea Ice

Record of Invention Number: 47655

Eric D'Asaro, Andrey Shcherbina

Disclosure

16 Mar 2016

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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