Rainville Luc

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Rainville
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Luc
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0000-0001-7337-225X

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Corrigendum to “Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation gyre” [Deep-Sea Res. II 85 (2013) 62–74]

2016-08-08 , Cronin, Meghan F. , Bond, Nicholas A. , Farrar, J. Thomas , Ichikawa, Hiroshi , Jayne, Steven R. , Kawai, Yoshimi , Konda, Masanori , Qiu, Bo , Rainville, Luc , Tomita, Hiroyuki

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Dynamics in the deep Canada Basin, Arctic Ocean, inferred by thermistor chain time series

2007-04 , Timmermans, Mary-Louise , Melling, Humfrey , Rainville, Luc

A 50-day time series of high-resolution temperature in the deepest layers of the Canada Basin in the Arctic Ocean indicates that the deep Canada Basin is a dynamically active environment, not the quiet, stable basin often assumed. Vertical motions at the near-inertial (tidal) frequency have amplitudes of 10– 20 m. These vertical displacements are surprisingly large considering the downward near-inertial internal wave energy flux typically observed in the Canada Basin. In addition to motion in the internal-wave frequency band, the measurements indicate distinctive subinertial temperature fluctuations, possibly due to intrusions of new water masses.

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Diurnal and semidiurnal internal tide energy flux at a continental slope in the South China Sea

2008-03-25 , Duda, Timothy F. , Rainville, Luc

Barotropic (surface) and baroclinic (internal) tides were measured at four mooring sites during a field investigation of acoustic propagation characteristics and physical oceanography in the northern South China Sea. The mooring positions were in a line moving up the shallow portion of a continental slope at water depths between 350 and 85 m. Using time series of temperature and velocity, at several depths, 1-month series of semidiurnal and diurnal species internal tidal energy flux vectors were computed for three sites, with a 14-day series computed for the fourth (shallow) site. The internal tides had a temporal signature that was not in complete accord with the barotropic tides, showing an enhancement of diurnal internal tides with respect to semidiurnal. Bathymetric slope, barotropic tidal fluid particle trajectories, and scale of generation site versus internal tide wavelength are investigated as possible causes of the differing response of the species.

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From salty to fresh—salinity processes in the Upper-ocean Regional Study-2 (SPURS-2) : diagnosing the physics of a rainfall-dominated salinity minimum

2015-03 , Schmitt, Raymond W. , Asher, William E. , Bingham, Frederick , Carton, James A. , Centurioni, Luca R. , Farrar, J. Thomas , Gordon, Arnold L. , Hodges, Benjamin A. , Jessup, Andrew T. , Kessler, William S. , Rainville, Luc , Shcherbina, Andrey Y.

One of the notable features of the global ocean is that the salinity of the North Atlantic is about 1 psu higher than that of the North Pacific. This contrast is thought to be due to one of the large asymmetries in the global water cycle: the transport of water vapor by the trade winds across Central America and the lack of any comparable transport into the Atlantic from the Sahara Desert. Net evaporation serves to maintain high Atlantic salinities, and net precipitation lowers those in the Pacific. Because the effects on upper-ocean physics are markedly different in the evaporating and precipitating regimes, the next phase of research in the Salinity Processes in the Upper-ocean Regional Study (SPURS) must address a high rainfall region. It seemed especially appropriate to focus on the eastern tropical Pacific that is freshened by the water vapor carried from the Atlantic. In a sense, the SPURS-2 Pacific region will be looking at the downstream fate of the freshwater carried out of the SPURS-1 North Atlantic region. Rainfall tends to lower surface density and thus inhibit vertical mixing, leading to quite different physical structure and dynamics in the upper ocean. Here, we discuss the motivations for the location of SPURS-2 and the scientific questions we hope to address.

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On the benefit of current and future ALPS data for improving Arctic coupled ocean-sea ice state estimation

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.

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Salinity and temperature balances at the SPURS central mooring during fall and winter

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.

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

2014-02 , Dosser, Hayley V. , Rainville, Luc , Toole, John M.

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

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Overview of the Arctic Sea state and boundary layer physics program

2018-04-16 , Thomson, Jim , Ackley, Stephen , Girard-Ardhuin, Fanny , Ardhuin, Fabrice , Babanin, Alexander , Boutin, Guillaume , Brozena, John , Cheng, Sukun , Collins, Clarence , Doble, Martin , Fairall, Christopher W. , Guest, Peter , Gebhardt, Claus , Gemmrich, Johannes , Graber, Hans C. , Holt, Benjamin , Lehner, Susanne , Lund, Björn , Meylan, Michael , Maksym, Ted , Montiel, Fabien , Perrie, Will , Persson, Ola , Rainville, Luc , Rogers, W. Erick , Shen, Hui , Shen, Hayley , Squire, Vernon , Stammerjohn, Sharon E. , Stopa, Justin , Smith, Madison M. , Sutherland, Peter , Wadhams, Peter

A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year.

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Preprint

The formation and fate of internal waves in the South China Sea

2015-03 , Alford, Matthew H. , Peacock, Thomas , MacKinnon, Jennifer A. , Nash, Jonathan D. , Buijsman, Maarten C. , Centurioni, Luca R. , Chao, Shenn-Yu , Chang, Ming-Huei , Farmer, David M. , Fringer, Oliver B. , Fu, Ke-Hsien , Gallacher, Patrick C. , Graber, Hans C. , Helfrich, Karl R. , Jachec, Steven M. , Jackson, Christopher R. , Klymak, Jody M. , Ko, Dong S. , Jan, Sen , Johnston, T. M. Shaun , Legg, Sonya , Lee, I-Huan , Lien, Ren-Chieh , Mercier, Matthieu J. , Moum, James N. , Musgrave, Ruth C. , Park, Jae-Hun , Pickering, Andrew I. , Pinkel, Robert , Rainville, Luc , Ramp, Steven R. , Rudnick, Daniel L. , Sarkar, Sutanu , Scotti, Alberto , Simmons, Harper L. , St Laurent, Louis C. , Venayagamoorthy, Subhas K. , Wang, Yu-Huai , Wang, Joe , Yang, Yiing-Jang , Paluszkiewicz, Theresa , Tang, Tswen Yung

Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they impact a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for manmade structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, posing severe challenges for their observation and their inclusion in numerical climate models, which are sensitive to their effects6-7. Over a decade of studies8-11 have targeted the South China Sea, where the oceans’ most powerful internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their generation mechanism, variability and energy budget, however, due to the lack of in-situ data from the Luzon Strait, where extreme flow conditions make measurements challenging. Here we employ new observations and numerical models to (i) show that the waves begin as sinusoidal disturbances rather than from sharp hydraulic phenomena, (ii) reveal the existence of >200-m-high breaking internal waves in the generation region that give rise to turbulence levels >10,000 times that in the open ocean, (iii) determine that the Kuroshio western boundary current significantly refracts the internal wave field emanating from the Luzon Strait, and (iv) demonstrate a factor-of-two agreement between modelled and observed energy fluxes that enables the first observationally-supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.

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

2012-07-21 , Cronin, Meghan F. , Bond, Nicholas A. , Farrar, J. Thomas , Ichikawa, Hiroshi , Jayne, Steven R. , Kawai, Yoshimi , Konda, Masanori , Qiu, Bo , Rainville, Luc , Tomita, Hiroyuki

Data from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the KE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3×10−4 m2/s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline.

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Preprint

Formation of Subtropical Mode Water in a high-resolution ocean simulation of the Kuroshio Extension region

2007-03-09 , Rainville, Luc , Jayne, Steven R. , McClean, Julie L. , Maltrud, Mathew E.

A high-resolution numerical model is used to examine the formation and variability of the North Pacific Subtropical ModeWater (STMW) over a 3-year period. The STMW distribution is found to be highly variable in both space and time, a characteristic often unexplored because of sparse observations or the use of coarse resolution simulations. Its distribution is highly dependent on eddies, and where it was renewed during the previous winter. Although the potential vorticity fluxes associated with down-front winds can be of the same order of magnitude or even greater than the diabatic ones due to air-sea temperature differences, the latter dominate the potential vorticity budget on regional and larger scales. Air-sea fluxes, however, are dominated by a few strong wind events, emphasizing the importance of short time scales in the formation of mode waters. In the Kuroshio Extension region, both advection and mixing play important roles to remove the STMW from the formation region.

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Moored observations of bottom-intensified motions in the deep Canada Basin, Arctic Ocean

2010-05-01 , Timmermans, Mary-Louise , Rainville, Luc , Thomas, Leif N. , Proshutinsky, Andrey

In the deep Canada Basin, below the sill depth (about 2400 m) of the Alpha-Mendeleyev Ridge, potential temperature and salinity first increase with depth, then remain uniform from about 2600 m to the bottom (approximately 3500 m). Year-long moored measurements of temperature, salinity and pressure in these deep and homogeneous bottom waters reveal significant vertical excursions with periods of about 50 days. The observed isopycnal displacements have amplitudes up to 100 m at the top boundary of the bottom layer; moored profiler measurements in the intermediate water column indicate that the amplitudes of these vertical displacements decay toward the surface over a scale of about 1000 m. The subinertial excursions are consistent with a bottom-trapped topographic Rossby wave. Given the magnitude of the bottom slope in the vicinity of the mooring, the observed vertical velocities correspond to only weak (about 1 cm s−1) cross-slope horizontal velocities. The generation mechanism for the waves remains an open question.

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Direct breaking of the internal tide near topography : Kaena Ridge, Hawaii

2008-02 , Klymak, Jody M. , Pinkel, Robert , Rainville, Luc

Barotropic to baroclinic conversion and attendant phenomena were recently examined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two distinct mixing processes appear to be at work in the waters above the 1100-m-deep ridge crest. At middepths, above 400 m, mixing events resemble their open-ocean counterparts. There is no apparent modulation of mixing rates with the fortnightly cycle, and they are well modeled by standard open-ocean parameterizations. Nearer to the topography, there is quasi-deterministic breaking associated with each baroclinic crest passage. Large-amplitude, small-scale internal waves are triggered by tidal forcing, consistent with lee-wave formation at the ridge break. These waves have vertical wavelengths on the order of 400 m. During spring tides, the waves are nonlinear and exhibit convective instabilities on their leading edge. Dissipation rates exceed those predicted by the open-ocean parameterizations by up to a factor of 100, with the disparity increasing as the seafloor is approached. These observations are based on a set of repeated CTD and microconductivity profiles obtained from the research platform (R/P) Floating Instrument Platform (FLIP), which was trimoored over the southern edge of the ridge crest. Ocean velocity and shear were resolved to a 4-m vertical scale by a suspended Doppler sonar. Dissipation was estimated both by measuring overturn displacements and from microconductivity wavenumber spectra. The methods agreed in water deeper than 200 m, where sensor resolution limitations do not limit the turbulence estimates. At intense mixing sites new phenomena await discovery, and existing parameterizations cannot be expected to apply.

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Autonomous multi-platform observations during the Salinity Processes in the Upper-ocean Regional Study

2017-06 , Lindstrom, Eric , Shcherbina, Andrey Y. , Rainville, Luc , Farrar, J. Thomas , Centurioni, Luca R. , Dong, Shenfu , D'Asaro, Eric A. , Eriksen, Charles C. , Fratantoni, David M. , Hodges, Benjamin A. , Hormann, Verena , Kessler, William S. , Lee, Craig M. , Riser, Stephen C. , St. Laurent, Louis C. , Volkov, Denis L.

The Salinity Processes in the Upper-ocean Regional Study (SPURS) aims to understand the patterns and variability of sea surface salinity. In order to capture the wide range of spatial and temporal scales associated with processes controlling salinity in the upper ocean, research vessels delivered autonomous instruments to remote sites, one in the North Atlantic and one in the Eastern Pacific. Instruments sampled for one complete annual cycle at each of these two sites, which are subject to contrasting atmospheric forcing. The SPURS field programs coordinated sampling from many different platforms, using a mix of Lagrangian and Eulerian approaches. This article discusses the motivations, implementation, and first results of the SPURS-1 and SPURS-2 programs.

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Preprint

The Kuroshio Extension and its recirculation gyres

2009-07-01 , Jayne, Steven R. , Hogg, Nelson G. , Waterman, Stephanie N. , Rainville, Luc , Donohue, Kathleen A. , Watts, D. Randolph , Tracey, Karen L. , McClean, Julie L. , Maltrud, Mathew E. , Qiu, Bo , Chen, Shuiming , Hacker, Peter

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

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Variations of the North Pacific Subtropical Mode Water from direct observations

2014-04-15 , Rainville, Luc , Jayne, Steven R. , Cronin, Meghan F.

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

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Novel and flexible approach to access the open ocean: Uses of sailing research vessel Lady Amber during SPURS-2.

2019-06-14 , Rainville, Luc , Centurioni, Luca R. , Asher, William E. , Clayson, Carol A. , Drushka, Kyla , Edson, James B. , Hodges, Benjamin A. , Hormann, Verena , Farrar, J. Thomas , Schanze, Julian J. , Shcherbina, Andrey Y.

SPURS-2 (Salinity Processes in the Upper-ocean Regional Study 2) used the schooner Lady Amber, a small sailing research vessel, to deploy, service, maintain, and recover a variety of oceanographic and meteorological instruments in the eastern Pacific Ocean. Low operational costs allowed us to frequently deploy floats and drifters to collect data necessary for resolving the regional circulation of the eastern tropical Pacific. The small charter gave us the opportunity to deploy drifters in locations chosen according to current conditions, to recover and deploy various autonomous instruments in a targeted and adaptive manner, and to collect additional near-surface and atmospheric measurements in the remote SPURS-2 region.

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Internal waves in the Arctic : influence of ice concentration, ice roughness, and surface layer stratification

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.

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Ice and ocean velocity in the Arctic marginal ice zone : ice roughness and momentum transfer

2017-09-21 , Cole, Sylvia T. , Toole, John M. , Lele, Ratnaksha , Timmermans, Mary-Louise , Gallaher, Shawn G. , Stanton, Timothy P. , Shaw, William J. , Hwang, Byongjun , Maksym, Ted , Wilkinson, Jeremy P. , Ortiz, Macarena , Graber, Hans C. , Rainville, Luc , Petty, Alek A. , Farrell, Sinéad L. , Richter-Menge, Jackie A. , Haas, Christian

The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations in the Canada Basin from March through December 2014 were used to investigate spatial differences and temporal changes in under-ice roughness and momentum transfer as the ice cover evolved seasonally. Observations of wind, ice, and ocean properties from four clusters of drifting instrument systems were complemented by direct drill-hole measurements and instrumented overhead flights by NASA operation IceBridge in March, as well as satellite remote sensing imagery about the instrument clusters. Spatially, directly estimated ice-ocean drag coefficients varied by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate. Temporal differences in the ice-ocean drag coefficient of 20–30% were observed prior to the mixed layer shoaling in summer and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest stratification. Wind work and ocean work on the ice were the dominant terms in the kinetic energy budget of the ice throughout the melt season, consistent with free drift conditions. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced mixed layer currents and the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations of momentum transfer, and imply that the future Arctic system could become increasingly seasonal.

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ASIRI : an ocean–atmosphere initiative for Bay of Bengal

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.