Lee Craig M.

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Craig M.

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  • Article
    Autonomous instruments significantly expand ocean observing : an introduction to the special issue on autonomous and Lagrangian platforms and sensors (ALPS).
    (Oceanography Society, 2017-06) Lee, Craig M. ; Paluszkiewicz, Theresa ; Rudnick, Daniel L. ; Omand, Melissa M. ; Todd, Robert E.
    Oceanography relies heavily on observations to fuel new ideas and drive advances, creating a strong coupling between the science and the technological developments that enable new measurements. Novel observations, such as those that resolve new properties or scales, often lead to advances in understanding. Physical, biological, and chemical processes unfold over a broad range of scales—seconds to decades and millimeters to ocean basins—with critical interactions between scales. Observational studies work within a tradespace that balances spatial and temporal resolution, scope, and resource constraints. New platforms and sensors, along with the novel observational approaches they enable, address this challenge by providing access to an expanding range of temporal and spatial scales.
  • Article
    Eddy-Kuroshio interaction processes revealed by mooring observations off Taiwan and Luzon
    (John Wiley & Sons, 2015-10-08) Tsai, Cheng-Ju ; Andres, Magdalena ; Jan, Sen ; Mensah, Vigan ; Sanford, Thomas B. ; Lien, Ren-Chieh ; Lee, Craig M.
    The influence and fate of westward propagating eddies that impinge on the Kuroshio were observed with pressure sensor-equipped inverted echo sounders (PIESs) deployed east of Taiwan and northeast of Luzon. Zero lag correlations between PIES-measured acoustic travel times and satellite-measured sea surface height anomalies (SSHa), which are normally negative, have lower magnitude toward the west, suggesting the eddy-influence is weakened across the Kuroshio. The observational data reveal that impinging eddies lead to seesaw-like SSHa and pycnocline depth changes across the Kuroshio east of Taiwan, whereas analogous responses are not found in the Kuroshio northeast of Luzon. Anticyclones intensify sea surface and pycnocline slopes across the Kuroshio, while cyclones weaken these slopes, particularly east of Taiwan. During the 6 month period of overlap between the two PIES arrays, only one anticyclone affected the pycnocline depth first at the array northeast of Luzon and 21 days later in the downstream Kuroshio east of Taiwan.
  • Preprint
    Surprising return of deep convection to the subpolar North Atlantic Ocean in winter 2007–2008
    ( 2008-11-07) Våge, Kjetil ; Pickart, Robert S. ; Thierry, Virginie ; Reverdin, Gilles ; Lee, Craig M. ; Petrie, Brian ; Agnew, Tom A. ; Wong, Amy ; Ribergaard, Mads H.
    The process of open-ocean convection in the subpolar North Atlantic Ocean forms a dense water mass that impacts the meridional overturning circulation and heat flux, and sequesters atmospheric carbon. In recent years the convection has been shallow or nonexistent, which could be construed as a consequence of a warmer climate. However, in the winter of 2007-08 deep convection returned to the subpolar gyre in both the Labrador and Irminger Seas. Here we document this return and elucidate the reasons why it happened. Profiling float data from the Argo programme are used to document the deep mixing, and a variety of in-situ, satellite, and reanalysis products are analyzed to describe the conditions leading to the overturning. The transition to a convective state took place abruptly, without going through a preconditioning phase, which is contrary to general expectations. Changes in the hemispheric air temperature, tracks of storms, flux of freshwater to the Labrador Sea, and distribution of pack ice all conspired to enhance the air-sea heat flux, resulting in the deep overturning. This study illuminates the complexity of the North Atlantic convective system.
  • Article
    The LatMix summer campaign : submesoscale stirring in the upper ocean
    (American Meteorological Society, 2015-08) Shcherbina, Andrey Y. ; Sundermeyer, Miles A. ; Kunze, Eric ; D'Asaro, Eric A. ; Badin, Gualtiero ; Birch, Daniel ; Brunner-Suzuki, Anne-Marie E. G. ; Callies, Joern ; Cervantes, Brandy T. Kuebel ; Claret, Mariona ; Concannon, Brian ; Early, Jeffrey ; Ferrari, Raffaele ; Goodman, Louis ; Harcourt, Ramsey R. ; Klymak, Jody M. ; Lee, Craig M. ; Lelong, M.-Pascale ; Levine, Murray D. ; Lien, Ren-Chieh ; Mahadevan, Amala ; McWilliams, James C. ; Molemaker, M. Jeroen ; Mukherjee, Sonaljit ; Nash, Jonathan D. ; Ozgokmen, Tamay M. ; Pierce, Stephen D. ; Ramachandran, Sanjiv ; Samelson, Roger M. ; Sanford, Thomas B. ; Shearman, R. Kipp ; Skyllingstad, Eric D. ; Smith, K. Shafer ; Tandon, Amit ; Taylor, John R. ; Terray, Eugene A. ; Thomas, Leif N. ; Ledwell, James R.
    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.
  • Article
    Downstream evolution of the Kuroshio's time-varying transport and velocity structure
    (John Wiley & Sons, 2017-05-02) Andres, Magdalena ; Mensah, Vigan ; Jan, Sen ; Chang, Ming-Huei ; Yang, Y.-J. ; Lee, Craig M. ; Ma, Barry ; Sanford, Thomas B.
    Observations from two companion field programs—Origins of the Kuroshio and Mindanao Current (OKMC) and Observations of Kuroshio Transport Variability (OKTV)—are used here to examine the Kuroshio's temporal and spatial evolution. Kuroshio strength and velocity structure were measured between June 2012 and November 2014 with pressure-sensor equipped inverted echo sounders (PIESs) and upward-looking acoustic Doppler current profilers (ADCPs) deployed across the current northeast of Luzon, Philippines, and east of Taiwan with an 8 month overlap in the two arrays' deployment periods. The time-mean net (i.e., integrated from the surface to the bottom) absolute transport increases downstream from 7.3 Sv (±4.4 Sv standard error) northeast of Luzon to 13.7 Sv (±3.6 Sv) east of Taiwan. The observed downstream increase is consistent with the return flow predicted by the simple Sverdrup relation and the mean wind stress curl field over the North Pacific (despite the complicated bathymetry and gaps along the North Pacific western boundary). Northeast of Luzon, the Kuroshio—bounded by the 0 m s−1 isotach—is shallower than 750 dbar, while east of Taiwan areas of positive flow reach to the seafloor (3000 m). Both arrays indicate a deep counterflow beneath the poleward-flowing Kuroshio (–10.3 ± 2.3 Sv by Luzon and −12.5 ± 1.2 Sv east of Taiwan). Time-varying transports and velocities indicate the strong influence at both sections of westward propagating eddies from the ocean interior. Topography associated with the ridges east of Taiwan also influences the mean and time-varying velocity structure there.
  • Article
    Greenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers
    (John Wiley & Sons, 2016-01-25) Dukhovskoy, Dmitry S. ; Myers, Paul G. ; Platov, Gennady A. ; Timmermans, Mary-Louise ; Curry, Beth ; Proshutinsky, Andrey ; Bamber, Jonathan L. ; Chassignet, Eric P. ; Hu, Xianmin ; Lee, Craig M. ; Somavilla, Raquel
    Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06–0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15–0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.
  • Article
    Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate
    (American Meteorological Society, 2014-07) Waterhouse, Amy F. ; MacKinnon, Jennifer A. ; Nash, Jonathan D. ; Alford, Matthew H. ; Kunze, Eric ; Simmons, Harper L. ; Polzin, Kurt L. ; St. Laurent, Louis C. ; Sun, Oliver M. T. ; Pinkel, Robert ; Talley, Lynne D. ; Whalen, Caitlin B. ; Huussen, Tycho N. ; Carter, Glenn S. ; Fer, Ilker ; Waterman, Stephanie N. ; Naveira Garabato, Alberto C. ; Sanford, Thomas B. ; Lee, Craig M.
    The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10−4) m2 s−1 and above 1000-m depth is O(10−5) m2 s−1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.
  • Article
    Studies of the Canadian Arctic Archipelago water transport and its relationship to basin-local forcings : results from AO-FVCOM
    (John Wiley & Sons, 2016-06-25) Zhang, Yu ; Chen, Changsheng ; Beardsley, Robert C. ; Gao, Guoping ; Lai, Zhigang ; Curry, Beth ; Lee, Craig M. ; Lin, Huichan ; Qi, Jianhua ; Xu, Qichun
    A high-resolution (up to 2 km), unstructured-grid, fully coupled Arctic sea ice-ocean Finite-Volume Community Ocean Model (AO-FVCOM) was employed to simulate the flow and transport through the Canadian Arctic Archipelago (CAA) over the period 1978–2013. The model-simulated CAA outflow flux was in reasonable agreement with the flux estimated based on measurements across Davis Strait, Nares Strait, Lancaster Sound, and Jones Sounds. The model was capable of reproducing the observed interannual variability in Davis Strait and Lancaster Sound. The simulated CAA outflow transport was highly correlated with the along-strait and cross-strait sea surface height (SSH) difference. Compared with the wind forcing, the sea level pressure (SLP) played a dominant role in establishing the SSH difference and the correlation of the CAA outflow with the cross-strait SSH difference can be explained by a simple geostrophic balance. The change in the simulated CAA outflow transport through Davis Strait showed a negative correlation with the net flux through Fram Strait. This correlation was related to the variation of the spatial distribution and intensity of the slope current over the Beaufort Sea and Greenland shelves. The different basin-scale surface forcings can increase the model uncertainty in the CAA outflow flux up to 15%. The daily adjustment of the model elevation to the satellite-derived SSH in the North Atlantic region outside Fram Strait could produce a larger North Atlantic inflow through west Svalbard and weaken the outflow from the Arctic Ocean through east Greenland.
  • Article
    Combining observations from multiple platforms across the Kuroshio northeast of Luzon : a highlight on PIES data
    (American Meteorological Society, 2016-10-05) Mensah, Vigan ; Andres, Magdalena ; Lien, Ren-Chieh ; Ma, Barry ; Lee, Craig M. ; Jan, Sen
    This study presents amended procedures to process and map data collected by pressure-sensor-equipped inverted echo sounders (PIESs) in western boundary current regions. The modifications to the existing methodology, applied to observations of the Kuroshio from a PIES array deployed northeast of Luzon, Philippines, consist of substituting a hydrography-based mean travel time field for the PIES-based mean field and using two distinct gravest empirical mode (GEM) lookup tables across the front that separate water masses of South China Sea and North Pacific origin. In addition, this study presents a method to use time-mean velocities from acoustic Doppler current profilers (ADCPs) to reference (or “level”) the PIES-recorded pressures in order to obtain time series of absolute geostrophic velocity. Results derived from the PIES observations processed with the hydrography-based mean field and two GEMs are compared with hydrographic profiles sampled by Seagliders during the PIES observation period and with current velocity measured concurrently by a collocated ADCP array. The updated processing scheme leads to a 41% error decrease in the determination of the thermocline depth across the current, a 22% error decrease in baroclinic current velocity shear, and a 61% error decrease in baroclinic volume transports. The absolute volume transport time series derived from the leveled PIES array compares well with that obtained directly from the ADCPs with a root-mean-square difference of 3.0 Sv (1 Sv ≡ 106 m3 s–1), which is mainly attributed to the influence of ageostrophic processes on the ADCP-measured velocities that cannot be calculated from the PIES observations.
  • Article
    Internal waves in the Arctic : influence of ice concentration, ice roughness, and surface layer stratification
    (John Wiley & Sons, 2018-08-14) Cole, Sylvia T. ; Toole, John M. ; Rainville, Luc ; Lee, Craig M.
    The Arctic ice cover influences the generation, propagation, and dissipation of internal waves, which in turn may affect vertical mixing in the ocean interior. The Arctic internal wavefield and its relationship to the ice cover is investigated using observations from Ice‐Tethered Profilers with Velocity and Seaglider sampling during the 2014 Marginal Ice Zone experiment in the Canada Basin. Ice roughness, ice concentration, and wind forcing all influenced the daily to seasonal changes in the internal wavefield. Three different ice concentration thresholds appeared to determine the evolution of internal wave spectral energy levels: (1) the initial decrease from 100% ice concentration after which dissipation during the surface reflection was inferred to increase, (2) the transition to 70–80% ice concentration when the local generation of internal waves increased, and (3) the transition to open water that was associated with larger‐amplitude internal waves. Ice roughness influenced internal wave properties for ice concentrations greater than approximately 70–80%: smoother ice was associated with reduced local internal wave generation. Richardson numbers were rarely supercritical, consistent with weak vertical mixing under all ice concentrations. On decadal timescales, smoother ice may counteract the effects of lower ice concentration on the internal wavefield complicating future predictions of internal wave activity and vertical mixing.
  • Article
    Biological structure and seasonality in the Japan/East Sea
    (Oceanography Society, 2006-09) Ashjian, Carin J. ; Arnone, Robert ; Davis, Cabell S. ; Jones, Burton ; Kahru, Mati ; Lee, Craig M. ; Mitchell, B. Gregory
    The Japan/East Sea (JES) contains several oceanic regions separated by dynamic boundaries. These distinct regions, and the physical features that establish and maintain the boundaries between the regions, have significant impacts on its ocean biology. Until recently, most studies of the biology of the JES have focused on nearshore regions, with few detailed studies of the interior of the JES or the dynamic features that define the different regions. In addition, the classic sampling methods used in previous work have not allowed high-resolution studies of biological-physical interactions associated with key dynamic mesoscale frontal zones, quasi-synoptic surveys of water column and biological structure in three dimensions, or broad-scale description of the seasonal cycles in the different biogeographic regions of the JES.
  • Article
    The Arctic freshwater system : changes and impacts
    (American Geophysical Union, 2007-11-20) White, Daniel ; Hinzman, Larry ; Alessa, Lilian ; Cassano, John ; Chambers, Molly ; Falkner, Kelly ; Francis, Jennifer ; Gutowski, William J. ; Holland, Marika M. ; Holmes, Robert M. ; Huntington, Henry ; Kane, Douglas ; Kliskey, Andrew ; Lee, Craig M. ; McClelland, James W. ; Peterson, Bruce J. ; Rupp, T. Scott ; Straneo, Fiamma ; Steele, Michael ; Woodgate, Rebecca ; Yang, Daqing ; Yoshikawa, Kenji ; Zhang, Tingjun
    Dramatic changes have been observed in the Arctic over the last century. Many of these involve the storage and cycling of fresh water. On land, precipitation and river discharge, lake abundance and size, glacier area and volume, soil moisture, and a variety of permafrost characteristics have changed. In the ocean, sea ice thickness and areal coverage have decreased and water mass circulation patterns have shifted, changing freshwater pathways and sea ice cover dynamics. Precipitation onto the ocean surface has also changed. Such changes are expected to continue, and perhaps accelerate, in the coming century, enhanced by complex feedbacks between the oceanic, atmospheric, and terrestrial freshwater systems. Change to the arctic freshwater system heralds changes for our global physical and ecological environment as well as human activities in the Arctic. In this paper we review observed changes in the arctic freshwater system over the last century in terrestrial, atmospheric, and oceanic systems.
  • Article
    Multipurpose acoustic networks in the integrated Arctic Ocean observing system
    (Arctic Institute of North America, 2015) Mikhalevsky, Peter N. ; Sagen, Hanne ; Worcester, Peter F. ; Baggeroer, Arthur B. ; Orcutt, John A. ; Moore, Sue E. ; Lee, Craig M. ; Vigness-Raposa, Kathleen J. ; Freitag, Lee E. ; Arrott, Matthew ; Atakan, Kuvvet ; Beszczynska-Möller, Agnieszka ; Duda, Timothy F. ; Dushaw, Brian D. ; Gascard, Jean-Claude ; Gavrilov, Alexander N. ; Keers, Henk ; Morozov, Andrey K. ; Munk, Walter H. ; Rixen, Michel ; Sandven, Stein ; Skarsoulis, Emmanuel ; Stafford, Kathleen M. ; Vernon, Frank L. ; Yuen, Mo Yan
    The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.
  • Article
    Bora event variability and the role of air-sea feedback
    (American Geophysical Union, 2007-02-13) Pullen, Julie ; Doyle, James D. ; Haack, Tracy ; Dorman, Clive E. ; Signell, Richard P. ; Lee, Craig M.
    A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS® is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ∼12% over the northern Adriatic during both bora compared with a one-way coupled simulation.
  • Article
    Observations of storm-induced mixing and Gulf Stream Ring incursion over the southern flank of Georges Bank : winter and summer 1997
    (American Geophysical Union, 2010-08-07) Lee, Craig M. ; Brink, Kenneth H.
    High-resolution hydrographic measurements collected along the southern edge of Georges Bank during March and June–July 1997 focused on characterizing processes that drive fluxes of material between the slope and bank. Wintertime sampling characterized changes driven by a strong storm. A Scotian Shelf crossover event produced a ribbon of anomalously fresh water along the bank's southern flank that was diluted during the storm. Comparison of prestorm and poststorm sections shows that over the bank changes in heat and salt inventories are consistent with those expected solely from local surface fluxes. In deeper waters, advective effects, likely associated with frontal motion and eddies, are clearly important. Summertime surveys resolve the development of a massive intrusion of Gulf Stream-like waters onto the bank. East of the intrusion, a thin extrusion of bank water is drawn outward by the developing ring, exporting fresher water at a rate of about 7 × 104 m3/s. A large-amplitude Gulf Stream meander appears to initiate the extrusion, but it quickly evolves, near the bank edge, into a warm core ring. Ring water intrudes to approximately the 80 m isobath, 40 km inshore from the bank edge. The intrusion process seems analogous to the development of Gulf Stream shingles (a hydrodynamic instability) in the South Atlantic Bight. It appears that, once the intruded water is established on the bank, it remains there and dissipates in place. Although the intrusion is an extremely dramatic event, it is probably not actually a major contributor to shelf edge exchanges over a seasonal time scale.
  • Article
    Circulation and intrusions northeast of Taiwan : chasing and predicting uncertainty in the cold dome
    (The Oceanography Society, 2011-12) Gawarkiewicz, Glen G. ; Jan, Sen ; Lermusiaux, Pierre F. J. ; McClean, Julie L. ; Centurioni, Luca R. ; Taylor, Kevin ; Cornuelle, Bruce D. ; Duda, Timothy F. ; Wang, Joe ; Yang, Yiing-Jang ; Sanford, Thomas B. ; Lien, Ren-Chieh ; Lee, Craig M. ; Lee, Ming-An ; Leslie, Wayne ; Haley, Patrick J. ; Niiler, Pearn P. ; Gopalakrishnan, Ganesh ; Velez-Belchi, Pedro ; Lee, Dong-Kyu ; Kim, Yoo Yin
    An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7–8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intrusions were associated with low sea surface height anomalies east of Taiwan, suggesting that there may be some degree of predictability for Kuroshio intrusions.
  • Article
    On the benefit of current and future ALPS data for improving Arctic coupled ocean-sea ice state estimation
    (Oceanography Society, 2017-06) Nguyen, An T. ; Ocana, Victor ; Garg, Vikram ; Heimbach, Patrick ; Toole, John M. ; Krishfield, Richard A. ; Lee, Craig M. ; Rainville, Luc
    Autonomous and Lagrangian platforms and sensors (ALPS) have revolutionized the way the subsurface ocean is observed. The synergy between ALPS-based observations and coupled ocean-sea ice state and parameter estimation as practiced in the Arctic Subpolar gyre sTate Estimate (ASTE) project is illustrated through several examples. In the western Arctic, Ice-Tethered Profilers have been providing important hydrographic constraints of the water column down to 800 m depth since 2004. ASTE takes advantage of these detailed constraints to infer vertical profiles of diapycnal mixing rates in the central Canada Basin. The state estimation framework is also used to explore the potential utility of Argo-type floats in regions with sparse data coverage, such as the eastern Arctic and the seasonal ice zones. Finally, the framework is applied to identify potential deployment sites that optimize the impact of float measurements on bulk oceanographic quantities of interest.
  • Article
    Salinity and temperature balances at the SPURS central mooring during fall and winter
    (The Oceanography Society, 2015-03) Farrar, J. Thomas ; Rainville, Luc ; Plueddemann, Albert J. ; Kessler, William S. ; Lee, Craig M. ; Hodges, Benjamin A. ; Schmitt, Raymond W. ; Edson, James B. ; Riser, Stephen C. ; Eriksen, Charles C. ; Fratantoni, David M.
    One part of the Salinity Processes in the Upper-ocean Regional Study (SPURS) field campaign focused on understanding the physical processes affecting the evolution of upper-ocean salinity in the region of climatological maximum sea surface salinity in the subtropical North Atlantic (SPURS-1). An upper-ocean salinity budget provides a useful framework for increasing this understanding. The SPURS-1 program included a central heavily instrumented mooring for making accurate measurements of air-sea surface fluxes, as well as other moorings, Argo floats, and gliders that together formed a dense observational array. Data from this array are used to estimate terms in the upper-ocean salinity and heat budgets during the SPURS-1 campaign, with a focus on the first several months (October 2012 to February 2013) when the surface mixed layer was becoming deeper, fresher, and cooler. Specifically, we examine the salinity and temperature balances for an upper-ocean mixed layer, defined as the layer where the density is within 0.4 kg m–3 of its surface value. The gross features of the evolution of upper-ocean salinity and temperature during this fall/winter season are explained by a combination of evaporation and precipitation at the sea surface, horizontal transport of heat and salt by mixed-layer currents, and vertical entrainment of fresher, cooler fluid into the layer as it deepened. While all of these processes were important in the observed seasonal (fall) freshening at this location in the salinity-maximum region, the variability of salinity on monthly-to-intraseasonal time scales resulted primarily from horizontal advection.
  • Article
    The Kuroshio and Luzon Undercurrent east of Luzon Island
    (The Oceanography Society, 2015-12) Lien, Ren-Chieh ; Ma, Barry ; Lee, Craig M. ; Sanford, Thomas B. ; Mensah, Vigan ; Centurioni, Luca R. ; Cornuelle, Bruce D. ; Gopalakrishnan, Ganesh ; Gordon, Arnold L. ; Chang, Ming-Huei ; Jayne, Steven R. ; Yang, Yiing-Jang
    Current structure, transport, and water mass properties of the northward-flowing Kuroshio and the southward-flowing Luzon Undercurrent (LU) were observed for nearly one year, June 8, 2012–June 4, 2013, across the Kuroshio path at 18.75°N. Observations were made from four platforms: an array of six subsurface ADCP moorings, two Seagliders, fivepressure inverted echo sounders (PIES), and five horizontal electric field (HEF) sensors, providing the most detailed time series of the Kuroshio and Luzon Undercurrent water properties to date. Ocean state estimates of the western boundary current system were performed using the MIT general circulation model—four-dimensional variational assimilation (MITgcm-4D-Var) system. Prominent Kuroshio features from observations are simulated well by the numerical model. Annual mean Kuroshio transport, averaged over all platforms, is ~16 Sv with a standard deviation ~4 Sv. Kuroshio and LU transports and water mass pathways east of Luzon are revealed by Seaglider measurements. In a layer above the salinity maximum associated with North Pacific Tropical Water (NPTW), Kuroshio transport is ~7 Sv and contains North Equatorial Current (NEC) and Western Philippine Sea (WPS) waters, with an insignificant amount of South China Sea water on the shallow western flank. In an intermediate layer containing the core of the NPTW, Kuroshio transport is ~10 Sv, consisting mostly of NEC water. In the lower layer of the Kuroshio, transport is ~1.5 Sv of mostly North Pacific Intermediate Water (NPIW) as a part of WPS waters. Annual mean Luzon Undercurrent southward transport integrated to 1,000 m depth is ~2.7 Sv with a standard deviation ~2 Sv, carrying solely WPS waters below the salinity minimum of the NPIW. The transport of the western boundary current integrated over the full ocean depth east of Luzon Island is ~14 ± 4.5 Sv. Sources of the water masses in the Kuroshio and Luzon Undercurrent are confirmed qualitatively by the numerical model.
  • Article
    ASIRI : an ocean–atmosphere initiative for Bay of Bengal
    (American Meteorological Society, 2016-11-22) Wijesekera, Hemantha W. ; Shroyer, Emily L. ; Tandon, Amit ; Ravichandran, M. ; Sengupta, Debasis ; Jinadasa, S. U. P. ; Fernando, Harindra J. S. ; Agrawal, Neeraj ; Arulananthan, India K. ; Bhat, G. S. ; Baumgartner, Mark F. ; Buckley, Jared ; Centurioni, Luca R. ; Conry, Patrick ; Farrar, J. Thomas ; Gordon, Arnold L. ; Hormann, Verena ; Jarosz, Ewa ; Jensen, Tommy G. ; Johnston, T. M. Shaun ; Lankhorst, Matthias ; Lee, Craig M. ; Leo, Laura S. ; Lozovatsky, Iossif ; Lucas, Andrew J. ; MacKinnon, Jennifer A. ; Mahadevan, Amala ; Nash, Jonathan D. ; Omand, Melissa M. ; Pham, Hieu ; Pinkel, Robert ; Rainville, Luc ; Ramachandran, Sanjiv ; Rudnick, Daniel L. ; Sarkar, Sutanu ; Send, Uwe ; Sharma, Rashmi ; Simmons, Harper L. ; Stafford, Kathleen M. ; St. Laurent, Louis C. ; Venayagamoorthy, Subhas K. ; Venkatesan, Ramasamy ; Teague, William J. ; Wang, David W. ; Waterhouse, Amy F. ; Weller, Robert A. ; Whalen, Caitlin B.
    Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view of the exchange along the periphery of Sri Lanka, which includes the 100-km-wide East India Coastal Current (EICC) carrying low-salinity water out of the BoB and an adjacent, broad northward flow (∼300 km wide) that carries high-salinity water into BoB during the northeast monsoon. Atmospheric boundary layer (ABL) observations during the decaying phase of the Madden–Julian oscillation (MJO) permit the study of multiscale atmospheric processes associated with non-MJO phenomena and their impacts on the marine boundary layer. Underway analyses that integrate observations and numerical simulations shed light on how air–sea interactions control the ABL and upper-ocean processes.