Rypina
Irina I.
Rypina
Irina I.
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ArticleInvestigating subsurface pathways of Fukushima cesium in the Northwest Pacific(American Geophysical Union, 20190618) Cedarholm, Ella R. ; Rypina, Irina I. ; Macdonald, Alison M. ; Yoshida, SachikoAdvective pathways for Fukushima Daiichi Nuclear Power Plant (FDNPP)‐derived cesium observed in 2013 at 166°E south of the Kuroshio Extension (KE) at >500 m on the 26.5σθ isopycnal are investigated. Attention is paid to the KE's role in shaping these pathways. Using a high‐resolution model, particle trajectories were simulated backward and forward in time on 26.5σθ between the 2013 observations and the 2011 source. A large fraction of backtracked trajectories interacted with the mixed layer just offshore of the FDNPP. The likeliest pathway reaching the deepest 2013 observed cesium location runs along the KE out to ~165°E, where it turns sharply southward. Forward trajectory statistics suggest that for 26.5σθ waters originating north of the KE, this current acted as a permeable barrier west of 155–160°E. The deepest 2011 model mixed layers suggest that FDNPP‐derived radionuclides may have been present at 30°N in 2013 at greater depths and densities (700 m; 26.8σθ).

ArticleChaotic advection in a steady, threedimensional, Ekmandriven eddy(Cambridge University Press, 20131205) Pratt, Lawrence J. ; Rypina, Irina I. ; Ozgokmen, Tamay M. ; Wang, P. ; Childs, H. ; Bebieva, Y.We investigate and quantify stirring due to chaotic advection within a steady, threedimensional, Ekmandriven, rotating cylinder flow. The flow field has vertical overturning and horizontal swirling motion, and is an idealization of motion observed in some ocean eddies. The flow is characterized by strong background rotation, and we explore variations in Ekman and Rossby numbers, E and Ro, over ranges appropriate for the ocean mesoscale and submesoscale. A highresolution spectral element model is used in conjunction with linear analytical theory, weakly nonlinear resonance analysis and a kinematic model in order to map out the barriers, manifolds, resonance layers and other objects that provide a template for chaotic stirring. As expected, chaos arises when a radially symmetric background state is perturbed by a symmetrybreaking disturbance. In the background state, each trajectory lives on a torus and some of the latter survive the perturbation and act as barriers to chaotic transport, a result consistent with an extension of the KAM theorem for threedimensional, volumepreserving flow. For shallow eddies, where E is O(1), the flow is dominated by thin resonant layers sandwiched between KAMtype barriers, and the stirring rate is weak. On the other hand, eddies with moderately small E experience thicker resonant layers, widerspread chaos and much more rapid stirring. This trend reverses for sufficiently small E, corresponding to deep eddies, where the vertical rigidity imposed by strong rotation limits the stirring. The bulk stirring rate, estimated from a passive tracer release, confirms the nonmonotonic variation in stirring rate with E. This result is shown to be consistent with linear Ekman layer theory in conjunction with a resonant width calculation and the Taylor–Proudman theorem. The theory is able to roughly predict the value of E at which stirring is maximum. For large disturbances, the stirring rate becomes monotonic over the range of Ekman numbers explored. We also explore variation in the eddy aspect ratio.

PreprintGeneralized Lagrangian coherent structures( 20180119) Balasuriya, Sanjeeva ; Ouellette, Nicholas T. ; Rypina, Irina I.The notion of a Lagrangian Coherent Structure (LCS) is by now well established as a way to capture transient coherent transport dynamics in unsteady and aperiodic fluid flows that are known over finite time. We show that the concept of an LCS can be generalized to capture coherence in other quantities of interest that are transported by, but not fully locked to, the fluid. Such quantities include those with dynamic, biological, chemical, or thermodynamic relevance, such as temperature, pollutant concentration, vorticity, kinetic energy, plankton density, and so on. We provide a conceptual framework for identifying the Generalized Lagrangian Coherent Structures (GLCSs) associated with such evolving quantities. We show how LCSs can be seen as a special case within this framework, and provide an overarching discussion of various methods for identifying LCSs. The utility of this more general viewpoint is highlighted through a variety of examples. We also show that although LCSs approximate GLCSs in certain limiting situations under restrictive assumptions on how the velocity field affects the additional quantities of interest, LCSs are not in general sufficient to describe their coherent transport.

ArticleInvestigating the connection between complexity of isolated trajectories and Lagrangian coherent structures(Copernicus Publications on behalf of the European Geosciences Union and the American Geophysical Union, 20111215) Rypina, Irina I. ; Scott, S. E. ; Pratt, Lawrence J. ; Brown, Michael G.It is argued that the complexity of fluid particle trajectories provides the basis for a new method, referred to as the Complexity Method (CM), for estimation of Lagrangian coherent structures in aperiodic flows that are measured over finite time intervals. The basic principles of the CM are explained and the CM is tested in a variety of examples, both idealized and realistic, and in different reference frames. Two measures of complexity are explored in detail: the correlation dimension of trajectory, and a new measure – the ergodicity defect. Both measures yield structures that strongly resemble Lagrangian coherent structures in all of the examples considered. Since the CM uses properties of individual trajectories, and not separation rates between closely spaced trajectories, it may have advantages for the analysis of ocean float and drifter data sets in which trajectories are typically widely and nonuniformly spaced.

ArticleInvestigating the eddy diffusivity concept in the coastal ocean(American Meteorological Society, 20160629) Rypina, Irina I. ; Kirincich, Anthony R. ; Lentz, Steven J. ; Sundermeyer, Miles A.This paper aims to test the validity, utility, and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a highresolution (800 m) highfrequency radar south of Martha’s Vineyard, Massachusetts. Specifically, this study investigates how well a combination of radarbased velocities and drifterderived diffusivities can reproduce observed dye spreading over an 8h time interval. A drifterbased estimate of an anisotropic diffusivity tensor is used to parameterize smallscale motions that are unresolved and underresolved by the radar system. This leads to a significant improvement in the ability of the radar to reproduce the observed dye spreading.

ArticleMode filters and energy conservation(Acoustical Society of America, 20100407) Udovydchenkov, Ilya A. ; Rypina, Irina I. ; Brown, Michael G.The discrete form of the mode filtering problem is considered. The relevant equations constitute a linear inverse problem. Solutions to problems of this type are subject to a wellknown tradeoff between resolution and precision. But unlike the typical linear inverse problem, the correctly formulated mode filtering problem is subject to an energy conservation constraint. This letter focuses on the importance of satisfying, approximately at least, the energy conservation constraint when mode filtering is performed.

ArticleNearsurface transport pathways in the north Atlantic Ocean : looking for throughput from the subtropical to the subpolar gyre(American Meteorological Society, 201105) Rypina, Irina I. ; Pratt, Lawrence J. ; Lozier, M. SusanMotivated by discrepancies between Eulerian transport estimates and the behavior of Lagrangian surface drifters, nearsurface transport pathways and processes in the North Atlantic are studied using a combination of data, altimetric surface heights, statistical analysis of trajectories, and dynamical systems techniques. Particular attention is paid to the issue of the subtropicaltosubpolar intergyre fluid exchange. The velocity field used in this study is composed of a steady drifterderived background flow, upon which a timedependent altimeterbased perturbation is superimposed. This analysis suggests that most of the fluid entering the subpolar gyre from the subtropical gyre within two years comes from a narrow region lying inshore of the Gulf Stream core, whereas fluid on the offshore side of the Gulf Stream is largely prevented from doing so by the Gulf Stream core, which acts as a strong transport barrier, in agreement with past studies. The transport barrier near the Gulf Stream core is robust and persistent from 1992 until 2008. The qualitative behavior is found to be largely independent of the Ekman drift.

ArticleRadiumbased estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident(Copernicus Publications on behalf of the European Geosciences Union, 20130328) Charette, Matthew A. ; Breier, Crystaline F. ; Henderson, Paul B. ; Pike, Steven M. ; Rypina, Irina I. ; Jayne, Steven R. ; Buesseler, Ken O.Radium has four naturally occurring isotopes that have proven useful in constraining water mass source, age, and mixing rates in the coastal and open ocean. In this study, we used radium isotopes to determine the fate and flux of runoffderived cesium from the Fukushima Daiichi Nuclear Power Plant (FNPP). During a June 2011 cruise, the highest cesium (Cs) concentrations were found along the eastern shelf of northern Japan, from Fukushima south, to the edge of the Kuroshio Current, and in an eddy ~ 130 km from the FNPP site. Locations with the highest cesium also had some of the highest radium activities, suggesting much of the direct ocean discharges of Cs remained in the coastal zone 2–3 months after the accident. We used a shortlived Ra isotope (223Ra, t1/2 = 11.4 d) to derive an average water mass age (Tr) in the coastal zone of 32 days. To groundtruth the Ra age model, we conducted a direct, stationbystation comparison of water mass ages with a numerical oceanographic model and found them to be in excellent agreement (model avg. Tr = 27 days). From these independent Tr values and the inventory of Cs within the water column at the time of our cruise, we were able to calculate an offshore 134Cs flux of 3.9–4.6 × 1013 Bq d−1. Radium228 (t1/2 = 5.75 yr) was used to derive a vertical eddy diffusivity (Kz) of 0.7 m2 d−1 (0.1 cm2 s−1); from this Kz and 134Cs inventory, we estimated a 134Cs flux across the pycnocline of 1.8 × 104 Bq d−1 for the same time period. On average, our results show that horizontal mixing loss of Cs from the coastal zone was ~ 109 greater than vertical exchange below the surface mixed layer. Finally, a mixing/dilution model that utilized our Rabased and oceanographic model water mass ages produced a direct ocean discharge of 134Cs from the FNPP of 11–16 PBq at the time of the peak release in early April 2011. Our results can be used to calculate discharge of other watersoluble radionuclides that were released to the ocean directly from the Fukushima NPP.

ArticleEddyinduced particle dispersion in the nearsurface North Atlantic(American Meteorological Society, 201212) Rypina, Irina I. ; Kamenkovich, Igor V. ; Berloff, Pavel S. ; Pratt, Lawrence J.This study investigates the anisotropic properties of the eddyinduced material transport in the nearsurface North Atlantic from two independent datasets, one simulated from the sea surface height altimetry and one derived from realocean surface drifters, and systematically examines the interactions between the mean and eddyinduced material transport in the region. The Lagrangian particle dispersion, which is widely used to characterize the eddyinduced tracer fluxes, is quantified by constructing the “spreading ellipses.” The analysis consistently demonstrates that this dispersion is spatially inhomogeneous and strongly anisotropic. The spreading is larger and more anisotropic in the subtropical than in the subpolar gyre, and the largest ellipses occur in the Gulf Stream vicinity. Even at times longer than half a year, the spreading exhibits significant nondiffusive behavior in some parts of the domain. The eddies in this study are defined as deviations from the longterm timemean. The contributions from the climatological annual cycle, interannual, and subannual (shorter than one year) variability are investigated, and the latter is shown to have the strongest effect on the anisotropy of particle spreading. The influence of the mean advection on the eddyinduced particle spreading is investigated using the “eddyfollowingfulltrajectories” technique and is found to be significant. The role of the Ekman advection is, however, secondary. The pronounced anisotropy of particle dispersion is expected to have important implications for distributing oceanic tracers, and for parameterizing eddyinduced tracer transfer in noneddyresolving models.

ArticleConnection between encounter volume and diffusivity in geophysical flows(Copernicus Publications on behalf of the European Geosciences Union, 20180404) Rypina, Irina I. ; Llewellyn Smith, Stefan ; Pratt, Lawrence J.Trajectory encounter volume – the volume of fluid that passes close to a reference fluid parcel over some time interval – has been recently introduced as a measure of mixing potential of a flow. Diffusivity is the most commonly used characteristic of turbulent diffusion. We derive the analytical relationship between the encounter volume and diffusivity under the assumption of an isotropic random walk, i.e., diffusive motion, in one and two dimensions. We apply the derived formulas to produce maps of encounter volume and the corresponding diffusivity in the Gulf Stream region of the North Atlantic based on satellite altimetry, and discuss the mixing properties of Gulf Stream rings. Advantages offered by the derived formula for estimating diffusivity from oceanographic data are discussed, as well as applications to other disciplines.

ArticleCompetition between chaotic advection and diffusion: Stirring and mixing in a 3D eddy model.(European Geosciences Union, 20190405) Brett, Genevieve ; Pratt, Lawrence J. ; Rypina, Irina I. ; Wang, PengThe importance of chaotic advection relative to turbulent diffusion is investigated in an idealized model of a 3D swirling and overturning ocean eddy. Various measures of stirring and mixing are examined in order to determine when and where chaotic advection is relevant. Turbulent diffusion is alternatively represented by (1) an explicit, observationbased, scaledependent diffusivity, (2) stochastic noise, added to a deterministic velocity field, or (3) explicit and implicit diffusion in a spectral numerical model of the Navier–Stokes equations. Lagrangian chaos in our model occurs only within distinct regions of the eddy, including a large chaotic “sea” that fills much of the volume near the perimeter and central axis of the eddy and much smaller “resonant” bands. The size and distribution of these regions depend on factors such as the degree of axial asymmetry of the eddy and the Ekman number. The relative importance of chaotic advection and turbulent diffusion within the chaotic regions is quantified using three measures: the Lagrangian Batchelor scale, the rate of dispersal of closely spaced fluid parcels, and the Nakamura effective diffusivity. The role of chaotic advection in the stirring of a passive tracer is generally found to be most important within the larger chaotic seas, at intermediate times, with small diffusivities, and for eddies with strong asymmetry. In contrast, in thin chaotic regions, turbulent diffusion at oceanographically relevant rates is at least as important as chaotic advection. Future work should address anisotropic and spatially varying representations of turbulent diffusion for more realistic models.

ArticleChaotic advection in an archipelago(American Meteorological Society, 201009) Rypina, Irina I. ; Pratt, Lawrence J. ; Pullen, Julie ; Levin, Julia C. ; Gordon, Arnold L.Techniques from dynamical systems theory have been applied to study horizontal stirring of fluid in the Philippine Archipelago. The authors’ analysis is based on velocity fields produced by two highresolution (3 and 6 km) numerical models. Particular attention is paid to identifying robust surface flow patterns and associating them with dominant Lagrangian coherent structures (LCSs). A recurrent winddriven dipole in the lee of the coastline is considered in detail. The associated LCSs form a template for stirring, exchange, and biological transport in and around the dipole. Chaotic advection is argued to provide a relevant framework for interpreting mesoscale horizontal stirring processes in an archipelago as a whole. Implications for the formation of filaments, the production of tracer variance, and the scale at which stirring leads to mixing are discussed in connection with an observed temperature record.

ArticleTrajectory encounter volume as a diagnostic of mixing potential in fluid flows(Copernicus Publications on behalf of the European Geosciences Union&the American Geophysical Union, 20170503) Rypina, Irina I. ; Pratt, Lawrence J.Fluid parcels can exchange water properties when coming into contact with each other, leading to mixing. The trajectory encounter mass and a related simplified quantity, the encounter volume, are introduced as a measure of the mixing potential of a flow. The encounter volume quantifies the volume of fluid that passes close to a reference trajectory over a finite time interval. Regions characterized by a low encounter volume, such as the cores of coherent eddies, have a low mixing potential, whereas turbulent or chaotic regions characterized by a large encounter volume have a high mixing potential. The encounter volume diagnostic is used to characterize the mixing potential in three flows of increasing complexity: the Duffing oscillator, the Bickley jet and the altimetrybased velocity in the Gulf Stream extension region. An additional example is presented in which the encounter volume is combined with the u approach of Pratt et al. (2016) to characterize the mixing potential for a specific tracer distribution in the Bickley jet flow. Analytical relationships are derived that connect the encounter volume to the shear and strain rates for linear shear and linear strain flows, respectively. It is shown that in both flows the encounter volume is proportional to time.

ArticleFukushimaderived radionuclides in the ocean and biota off Japan(National Academy of Sciences, 20120402) Buesseler, Ken O. ; Jayne, Steven R. ; Fisher, Nicholas S. ; Rypina, Irina I. ; Baumann, Hannes ; Baumann, Zofia ; Breier, Crystaline F. ; Douglass, Elizabeth M. ; George, Jennifer ; Macdonald, Alison M. ; Miyamoto, Hiroomi ; Nishikawa, Jun ; Pike, Steven M. ; Yoshida, Sachiko

ArticleEulerian and Lagrangian correspondence of highfrequency radar and surface drifter data : effects of radar resolution and flow components(American Meteorological Society, 201404) Rypina, Irina I. ; Kirincich, Anthony R. ; Limeburner, Richard ; Udovydchenkov, Ilya A.This study investigated the correspondence between the nearsurface drifters from a mass drifter deployment near Martha’s Vineyard, Massachusetts, and the surface current observations from a network of three highresolution, highfrequency radars to understand the effects of the radar temporal and spatial resolution on the resulting Eulerian current velocities and Lagrangian trajectories and their predictability. The radarbased surface currents were found to be unbiased in direction but biased in magnitude with respect to drifter velocities. The radar systematically underestimated velocities by approximately 2 cm s−1 due to the smoothing effects of spatial and temporal averaging. The radar accuracy, quantified by the domainaveraged rms difference between instantaneous radar and drifter velocities, was found to be about 3.8 cm s−1. A Lagrangian comparison between the real and simulated drifters resulted in the separation distances of roughly 1 km over the course of 10 h, or an equivalent separation speed of approximately 2.8 cm s−1. The effects of the temporal and spatial radar resolution were examined by degrading the radar fields to coarser resolutions, revealing the existence of critical scales (1.5–2 km and 3 h) beyond which the ability of the radar to reproduce drifter trajectories decreased more rapidly. Finally, the importance of the different flow components present during the experiment—mean, tidal, locally winddriven currents, and the residual velocities—was analyzed, finding that, during the study period, a combination of tidal, locally winddriven, and mean currents were insufficient to reliably reproduce, with minimal degradation, the trajectories of real drifters. Instead, a minimum combination of the tidal and residual currents was required.

ArticleShortterm dispersal of Fukushimaderived radionuclides off Japan : modeling efforts and modeldata intercomparison(Copernicus Publications on behalf of the European Geosciences Union, 20130724) Rypina, Irina I. ; Jayne, Steven R. ; Yoshida, Sachiko ; Macdonald, Alison M. ; Douglass, Elizabeth M. ; Buesseler, Ken O.The Great East Japan Earthquake and tsunami that caused a loss of power at the Fukushima nuclear power plants (FNPP) resulted in emission of radioactive isotopes into the atmosphere and the ocean. In June of 2011, an international survey measuring a variety of radionuclide isotopes, including 137Cs, was conducted in surface and subsurface waters off Japan. This paper presents the results of numerical simulations specifically aimed at interpreting these observations and investigating the spread of Fukushimaderived radionuclides off the coast of Japan and into the greater Pacific Ocean. Together, the simulations and observations allow us to study the dominant mechanisms governing this process, and to estimate the total amount of radionuclides in discharged coolant waters and atmospheric airborne radionuclide fallout. The numerical simulations are based on two different ocean circulation models, one inferred from AVISO altimetry and NCEP/NCAR reanalysis wind stress, and the second generated numerically by the NCOM model. Our simulations determine that > 95% of 137Cs remaining in the water within ~600 km of Fukushima, Japan in midJune 2011 was due to the direct oceanic discharge. The estimated strength of the oceanic source is 16.2 ± 1.6 PBq, based on minimizing the modeldata mismatch. We cannot make an accurate estimate for the atmospheric source strength since most of the fallout cesium had left the survey area by midJune. The model explained several key features of the observed 137Cs distribution. First, the absence of 137Cs at the southernmost stations is attributed to the Kuroshio Current acting as a transport barrier against the southward progression of 137Cs. Second, the largest 137Cs concentrations were associated with a semipermanent eddy that entrained 137Csrich waters, collecting and stirring them around the eddy perimeter. Finally, the intermediate 137Cs concentrations at the westernmost stations are attributed to younger, and therefore less Csrich, coolant waters that continued to leak from the reactor in June of that year.

ArticleProperties and origins of the anisotropic eddyinduced transport in the North Atlantic(American Meteorological Society, 201503) Kamenkovich, Igor V. ; Rypina, Irina I. ; Berloff, Pavel S.This study examines anisotropic transport properties of the eddying North Atlantic flow, using an idealized model of the doublegyre oceanic circulation and altimetryderived velocities. The material transport by the timedependent flow (quantified by the eddy diffusivity tensor) varies geographically and is anisotropic, that is, it has a welldefined direction of the maximum transport. One component of the timedependent flow, zonally elongated largescale transients, is particularly important for the anisotropy, as it corresponds to primarily zonal material transport and long correlation time scales. The importance of these largescale zonal transients in the material distribution is further confirmed with simulations of idealized color dye tracers, which has implications for parameterizations of the eddy transport in noneddyresolving models.

PreprintAssimilating Lagrangian data for parameter estimation in a multipleinlet system( 201704) Slivinski, Laura ; Pratt, Lawrence J. ; Rypina, Irina I. ; Orescanin, Mara M. ; Raubenheimer, Britt ; MacMahan, Jamie ; Elgar, SteveNumerical models of ocean circulation often depend on parameters that must be tuned to match either results from laboratory experiments or field observations. This study demonstrates that an initial, suboptimal estimate of a parameter in a model of a small bay can be improved by assimilating observations of trajectories of passive drifters. The parameter of interest is the Manning's n coefficient of friction in a small inlet of the bay, which had been tuned to match velocity observations from 2011. In 2013, the geometry of the inlet had changed, and the friction parameter was no longer optimal. Results from synthetic experiments demonstrate that assimilation of drifter trajectories improves the estimate of n, both when the drifters are located in the same region as the parameter of interest and when the drifters are located in a different region of the bay. Real drifter trajectories from field experiments in 2013 also are assimilated, and results are compared with velocity observations. When the real drifters are located away from the region of interest, the results depend on the time interval (with respect to the full available trajectories) over which assimilation is performed. When the drifters are in the same region as the parameter of interest, the value of n estimated with assimilation yields improved estimates of velocity throughout the bay.

ArticleDrifterbased estimate of the 5 year dispersal of Fukushimaderived radionuclides(John Wiley & Sons, 20141128) Rypina, Irina I. ; Jayne, Steven R. ; Yoshida, Sachiko ; Macdonald, Alison M. ; Buesseler, Ken O.Employing some 40 years of North Pacific driftertrack observations from the Global Drifter Program database, statistics defining the horizontal spread of radionuclides from Fukushima nuclear power plant into the Pacific Ocean are investigated over a time scale of 5 years. A novel twoiteration method is employed to make the best use of the available drifter data. Drifterbased predictions of the temporal progression of the leading edge of the radionuclide distribution are compared to observed radionuclide concentrations from research surveys occupied in 2012 and 2013. Good agreement between the drifterbased predictions and the observations is found.

ArticleMultiiteration approach to studying tracer spreading using drifter data(American Meteorological Society, 20170131) Rypina, Irina I. ; Fertitta, David ; Macdonald, Alison M. ; Yoshida, Sachiko ; Jayne, Steven R.A novel multiiteration statistical method for studying tracer spreading using drifter data is introduced. The approach allows for the best use of the available drifter data by making use of a simple iterative procedure, which results in the statistically probable map showing the likelihood that a tracer released at some source location would visit different geographical regions, along with the associated arrival travel times. The technique is tested using real drifter data in the North Atlantic. Two examples are considered corresponding to sources in the western and eastern North Atlantic Ocean, that is, Massachusetts Bay–like and Irish Sea–like sources, respectively. In both examples, the method worked well in estimating the statistics of the tracer transport pathways and travel times throughout the entire North Atlantic. The role of eddies versus mean flow is quantified using the same technique, and eddies are shown to significantly broaden the spread of a tracer. The sensitivity of the results to the size of the source domain is investigated and causes for this sensitivity are discussed.