Showing papers in "Journal of Physical Oceanography in 2018"
TL;DR: In this article, the transition from balanced geostrophic motions to unbalanced wave motions, including near-inertial flows, internal tides, and inertia-gravity wave continuum, was explored using the output from a global 1/48° horizontal resolution Massachusetts Institute of Technology general circulation model (MITgcm) simulation.
Abstract: The transition scale Lt from balanced geostrophic motions to unbalanced wave motions, including near-inertial flows, internal tides, and inertia–gravity wave continuum, is explored using the output from a global 1/48° horizontal resolution Massachusetts Institute of Technology general circulation model (MITgcm) simulation. Defined as the wavelength with equal balanced and unbalanced motion kinetic energy (KE) spectral density, Lt is detected to be geographically highly inhomogeneous: it falls below 40 km in the western boundary current and Antarctic Circumpolar Current regions, increases to 40–100 km in the interior subtropical and subpolar gyres, and exceeds, in general, 200 km in the tropical oceans. With the exception of the Pacific and Indian sectors of the Southern Ocean, the seasonal KE fluctuations of the surface balanced and unbalanced motions are out of phase because of the occurrence of mixed layer instability in winter and trapping of unbalanced motion KE in shallow mixed layer in summe...
111 citations
TL;DR: The Barents Sea Water (BSW) as mentioned in this paper is formed from Atlantic Water that is cooled through atmospheric heat loss and freshened through seasonal sea ice melt, and it is a mixture of Atlantic Water and fresh sea ice.
Abstract: Barents Sea Water (BSW) is formed from Atlantic Water that is cooled through atmospheric heat loss and freshened through seasonal sea ice melt. In the eastern Barents Sea, the BSW and fresh...
107 citations
TL;DR: In this paper, the authors presented observational estimates of Ekman pumping in the Beaufort Gyre region Averaged over the Canada Basin, the results show a 2003-14 average of 23m yr−1 downward with strong seasonal and interannual variability superimposed: monthly and yearly means range from 30 m yr− 1 downward to 10 m yr −1 upward.
Abstract: We present observational estimates of Ekman pumping in the Beaufort Gyre region Averaged over the Canada Basin, the results show a 2003–14 average of 23 m yr−1 downward with strong seasonal and interannual variability superimposed: monthly and yearly means range from 30 m yr−1 downward to 10 m yr−1 upward A clear, seasonal cycle is evident with intense downwelling in autumn and upwelling during the winter months, despite the wind forcing being downwelling favorable year-round Wintertime upwelling is associated with friction between the large-scale Beaufort Gyre ocean circulation and the surface ice pack and contrasts with previous estimates of yearlong downwelling; as a consequence, the yearly cumulative Ekman pumping over the gyre is significantly reduced The spatial distribution of Ekman pumping is also modified, with the Beaufort Gyre region showing alternating, moderate upwelling and downwelling, while a more intense, yearlong downwelling averaging 18 m yr−1 is identified in the northern
60 citations
TL;DR: In this article, the relationship between net mixing and the estuarine exchange flow was quantified using a salinity variance budget, where mixing is defined as the rate of destruction of volume-integrated saliency variance, and the exchange flow is quantified by the Total Exchange Flow.
Abstract: The relationship between net mixing and the estuarine exchange flow may be quantified using a salinity variance budget. Here “mixing” is defined as the rate of destruction of volume-integrated salinity variance, and the exchange flow is quantified using the Total Exchange Flow. These concepts are explored using an idealized 3-D model estuary. It is shown that in steady state (e.g. averaging over the spring-neap cycle) the volume-integrated mixing is approximately given by Mixing ≅ SinSoutQr, where Sin and Sout are the representative salinities of in- and out-flowing layers at the mouth, and Qr is the river volume flux. This relationship provides an extension of the familiar Knudsen relation, in which the exchange flow is diagnosed based on knowledge of these same three quantities, quantitatively linking mixing to the exchange flow.
52 citations
TL;DR: In this article, the authors present results from an observational field program in southern Drake Passage, a region preconditioned for submesoscale instability due to its strong mesoscale eddy field, persistent fronts, strong down-front winds, and weak vertical stratification.
Abstract: Enhanced vertical velocities associated with submesoscale motions may rapidly modify mixed layer depths and increase exchange between the mixed layer and the ocean interior. These dynamics are of particular importance in the Southern Ocean, where the ventilation of many density classes occurs. Here we present results from an observational field program in southern Drake Passage, a region preconditioned for submesoscale instability due to its strong mesoscale eddy field, persistent fronts, strong down-front winds, and weak vertical stratification. Two gliders sampled from December 2014 through March 2015 upstream and downstream of Shackleton Fracture Zone (SFZ). The acquired time series of mixed layer depths and buoyancy gradients enabled calculations of potential vorticity and classifications of submesoscale instabilities. The regions flanking the SFZ displayed remarkably different characteristics despite similar surface forcing. Mixed layer depths were nearly twice as deep and horizontal buoyancy...
51 citations
TL;DR: The strong stratification of the Bay of Bengal (BoBWB) causes rapid variations in sea surface temperature (SST) that influence the development of monsoon rainfall systems as discussed by the authors.
Abstract: The strong stratification of the Bay of Bengal (BoB) causes rapid variations in sea surface temperature (SST) that influence the development of monsoon rainfall systems. This stratification...
50 citations
TL;DR: In this paper, a large-eddy simulation (LES) was used to simulate turbulent flow over strongly forced steep steady and unsteady waves, with time t and space x varying wave height h(x, t) imposed as a lower boundary condition.
Abstract: Turbulent flow over strongly forced steep steady and unsteady waves is simulated using large-eddy simulation (LES) with time t and space x varying wave height h(x, t) imposed as a lower boundary condition. With steady waves, h(x, t) is based on measurements of incipient and active breaking waves collected in a wind-wave flume, while a numerical wave code is used to generate an unsteady evolving wave packet (group). Highly intermittent airflow separation is found in the simulations, and the results suggest separation near a wave crest occurs prior to the onset of wave breaking. The form (pressure) drag is most sensitive to the wave slope, and the form drag can contribute as much as 74% to the total stress. Wind and scalar profiles from the LES display log-linear variations above the wave surface; the LES wind profiles are in good agreement with the measurements. The momentum roughness increases as the water surface changes from wind ripples to incipient breaking to active breaking. However, the sca...
47 citations
TL;DR: Weakly stratified layers over sloping topography can support a submesoscale baroclinic instability mode, a bottom boundary layer counterpart to surface mixed layer instabilities as mentioned in this paper.
Abstract: Weakly stratified layers over sloping topography can support a submesoscale baroclinic instability mode, a bottom boundary layer counterpart to surface mixed layer instabilities. The instab...
47 citations
TL;DR: In this article, the authors describe the results of an experimental and theoretical investigation into the mechanisms by which spume droplets are generated by high winds, and the experiments were performed in...
Abstract: This paper describes the results of an experimental and theoretical investigation into the mechanisms by which spume droplets are generated by high winds. The experiments were performed in ...
46 citations
TL;DR: In this paper, microstructure, current, and hydrography observations from June 2016 are used to characterize the turbulence structure of the Lofoten Basin eddy (LBE), a long-lived anticyclone in the...
Abstract: Ocean microstructure, current, and hydrography observations from June 2016 are used to characterize the turbulence structure of the Lofoten Basin eddy (LBE), a long-lived anticyclone in the...
42 citations
TL;DR: In this article, a seasonally forced 1/12° global ocean/sea ice simulation is used to characterize the spatiotemporal inverse cascade of kinetic energy (KE), and nonlinear scale interactions associated with rel...
Abstract: A seasonally forced 1/12° global ocean/sea ice simulation is used to characterize the spatiotemporal inverse cascade of kinetic energy (KE). Nonlinear scale interactions associated with rel...
TL;DR: In this paper, heat and momentum transfer across the wind-driven breaking air-water interface at extremely high wind speeds was experimentally investigated using a high-speed wind-wave tank.
Abstract: Heat and momentum transfer across the wind-driven breaking air–water interface at extremely high wind speeds was experimentally investigated using a high-speed wind-wave tank. An original m...
TL;DR: Using multiscale window transform (MWT) and canonical energy transfer theory, the authors investigated the seasonal eddy variability in the Kuroshio Sea, and found that MWT-based MWT can be used to transfer energy from one season to another.
Abstract: Using a recently developed tool, multiscale window transform (MWT), and the MWT-based canonical energy transfer theory, this study investigates the seasonal eddy variability in the Kuroshio...
TL;DR: In this paper, the drag and turbulence in steady stratified flows over "abyssal hills" have been parameterized using linear theory and rates of energy cascade due to wave-wave interactions.
Abstract: Drag and turbulence in steady stratified flows over “abyssal hills” have been parameterized using linear theory and rates of energy cascade due to wave–wave interactions. Linear theory has ...
TL;DR: In this article, the role of Southern Ocean warm intermediate water for driving melting of the Antarctic ice sheet is determined, which is a major challenge in assessing future sea level rise, based on analysis of 2859 CTD p...
Abstract: Determining the role of Southern Ocean warm intermediate water for driving melting of the Antarctic ice sheet is a major challenge in assessing future sea level rise. Analysis of 2859 CTD p...
TL;DR: Rotation coherent Lagrangian vortices (RCLVs) were identified from satellite-derived surface geostrophic velocities in the eastern Pacific (180°-130°W) using the objective (frame invaria) as mentioned in this paper.
Abstract: Rotationally coherent Lagrangian vortices (RCLVs) are identified from satellite-derived surface geostrophic velocities in the eastern Pacific (180°–130°W) using the objective (frame invaria
TL;DR: In this paper, lateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central Bay of Bengal during the winter monsoon were explored using high-resolved sensors.
Abstract: Lateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central Bay of Bengal during the winter monsoon are explored using high-resol...
TL;DR: In this article, a long time series of the upper Maluku Channel transport is measured successfully for the first time using subsurface oceanic moorings and the results suggest the importance of the western boundary current nonlinearity in driving the transport variability of the Indonesian Throughflow.
Abstract: The Maluku Channel is a major opening of the eastern Indonesian Seas to the western Pacific Ocean, the upper-ocean currents of which have rarely been observed historically. During December 2012-November 2016, long time series of the upper Maluku Channel transport are measured successfully for the first time using subsurface oceanic moorings. The measurements show significant intraseasonal-to-interannual variability of over 14 Sv (1 Sv 10(6) m(3) s(-1)) in the upper 300 m or so, with a mean transport of 1.04-1.31 Sv northward and a significant southward interannual change of over 3.5 Sv in the spring of 2014. Coincident with the interannual transport change is the Mindanao Current, choked at the entrance of the Indonesian Seas, which is significantly different from its climatological retroflection in fall-winter. A high-resolution numerical simulation suggests that the variations of the Maluku Channel currents are associated with the shifting of the Mindanao Current retroflection. It is suggested that the shifting of the Mindanao Current outside the Sulawesi Sea in the spring of 2014 elevates the sea level at the entrance of the Indonesian Seas, which drives the anomalous transport through the Maluku Channel. The results suggest the importance of the western boundary current nonlinearity in driving the transport variability of the Indonesian Throughflow.
TL;DR: In this article, the seasonal cycle of ocean and sea ice heat and freshwater fluxes around the Arctic Ocean boundary is estimated, and the ocean transports are estimated primarly based on the first estimate.
Abstract: This paper presents the first estimate of the seasonal cycle of ocean and sea ice heat and freshwater (FW) fluxes around the Arctic Ocean boundary. The ocean transports are estimated primar...
TL;DR: An intrahalocline eddy was observed on the Chukchi slope in September of 2015 using both towed CTD and microstructure temperature and shear sections as mentioned in this paper.
Abstract: An intrahalocline eddy was observed on the Chukchi slope in September of 2015 using both towed CTD and microstructure temperature and shear sections. The core of the eddy was 6°C, significa...
TL;DR: In this article, the authors used deep microstructure profiles collected in various regions of the North Pacific and the Southern Ocean to estimate the dissipation flux coefficient in the Osborn's eddy diffusivity model.
Abstract: Recent progress in direct numerical simulations (DNS) of stratified turbulent flows has led to increasing attention to the validity of the constancy of the dissipation flux coefficient Г in the Osborn’s eddy diffusivity model. Motivated by lack of observational estimates of Г particularly under weakly stratified deep-ocean conditions, this study estimates Г using deep microstructure profiles collected in various regions of the North Pacific and the Southern Ocean. It is shown that Г is not constant but varies significantly with the Ozmidov/Thorpe scale ratio ROT in a fashion similar to that obtained by previous DNS studies. Efficient mixing events with Г ~ O(1) and ROT ~ O(0:1) tend to be frequently observed in the deep ocean (i.e., weak stratification), while moderate mixing events with Г ~ O(0:1) and ROT ~ O(1) tend to be observed in the upper ocean (i.e., strong stratification). The observed negative relationship between Г and ROT is consistent with a simple scaling that can be derived from cla...
TL;DR: In this article, the authors quantified the relative energy loss from the time-mean and transient eddy flow in the Southern Ocean due to lee wave generation using an eddy-resolving global ocean model and three independent topographic datasets.
Abstract: Observations suggest that enhanced turbulent dissipation and mixing over rough topography are modulated by the transient eddy field through the generation and breaking of lee waves in the Southern Ocean. Idealized simulations also suggest that lee waves are important in the energy pathway from eddies to turbulence. However, the energy loss from eddies due to lee wave generation remains poorly estimated. This study quantifies the relative energy loss from the time-mean and transient eddy flow in the Southern Ocean due to lee wave generation using an eddy-resolving global ocean model and three independent topographic datasets. The authors find that the energy loss from the transient eddy flow (0.12 TW; 1 TW = 1012 W) is larger than that from the time-mean flow (0.04 TW) due to lee wave generation; lee wave generation makes a larger contribution (0.12 TW) to the energy loss from the transient eddy flow than the dissipation in turbulent bottom boundary layer (0.05 TW). This study also shows that the energy loss from the time-mean flow is regulated by the transient eddy flow, and energy loss from the transient eddy flow is sensitive to the representation of anisotropy in small-scale topography. It is implied that lee waves should be parameterized in eddy-resolving global ocean models to improve the energetics of resolved flow.
TL;DR: In this paper, the importance of the hydrodynamic roughness scale on the bottom of a flow over complex terrain was emphasized, leading to drag, turbulence, and formation of a boundary layer.
Abstract: Flow over complex terrain causes stress on the bottom leading to drag, turbulence, and formation of a boundary layer. But despite the importance of the hydrodynamic roughness scale z0 in pr...
TL;DR: In this article, the influence of submesoscale currents on the distribution and subduction of passive, buoyant tracers in the mixed layer is examined using large-eddy simulations.
Abstract: The influence of submesoscale currents on the distribution and subduction of passive, buoyant tracers in the mixed layer is examined using large-eddy simulations. Submesoscale eddies are generated through an ageostrophic baroclinic instability associated with a background horizontal buoyancy gradient. The simulations also include various levels of surface cooling, which provides an additional source of three-dimensional turbulence. Submesoscales compete against turbulent convection and restratify the mixed layer while generating strong turbulence along a submesoscale front. Buoyant tracers accumulate at the surface along the submesoscale front where they are subducted down into the water column. The presence of submesoscales strongly modifies the vertical tracer flux, even in the presence of strong convective forcing. The correlation between high tracer concentration and strong downwelling enhances the vertical diffusivity for buoyant tracers.
TL;DR: In this paper, the role of mesoscale eddies in modulating the semidiurnal internal tide in the northern South China Sea (SCS) was examined using the data from a cross-shaped mooring array.
Abstract: The role of mesoscale eddies in modulating the semidiurnal internal tide (SIT) in the northern South China Sea (SCS) is examined using the data from a cross-shaped mooring array. From Novem...
TL;DR: The global stratification and circulation, as well as their sensitivities to changes in forcing, depend crucially on the representation of the mesoscale eddy field in a numerical ocean circ... as discussed by the authors.
Abstract: The global stratification and circulation, as well as their sensitivities to changes in forcing, depend crucially on the representation of the mesoscale eddy field in a numerical ocean circ...
TL;DR: Nonconservative processes change the potential vorticity (PV) of the upper ocean and, later, through the subduction of surface waters into the interior, affect the general ocean circulation as discussed by the authors.
Abstract: Nonconservative processes change the potential vorticity (PV) of the upper ocean and, later, through the subduction of surface waters into the interior, affect the general ocean circulation...
TL;DR: In this article, the wave statistical properties and occurrence of extreme and rogue waves in crossing sea states are investigated, and compared to previous studies, a more extensive set of crossings states are compared.
Abstract: Wave statistical properties and occurrence of extreme and rogue waves in crossing sea states are investigated. Compared to previous studies a more extensive set of crossing sea states are i...
TL;DR: In this article, the life cycle of semidiurnal internal tides over the Mid-Atlantic Ridge (MAR) sector south of the Azores is investigated using in situ, a high-resolution mooring and microstructure profiler, and satellite data, in combination with a theoretical model of barotropic-to-baroclinic tidal energy conversion.
Abstract: The life cycle of semidiurnal internal tides over the Mid-Atlantic Ridge (MAR) sector south of the Azores is investigated using in situ, a high-resolution mooring and microstructure profiler, and satellite data, in combination with a theoretical model of barotropic-to-baroclinic tidal energy conversion. The mooring analysis reveals that the internal tide horizontal energy flux is dominated by mode 1 and that energy density is more distributed among modes 1–10. Most modes are compatible with an interpretation in terms of standing internal tides, suggesting that they result from interactions between waves generated over the MAR. Internal tide energy is thus concentrated above the ridge and is eventually available for local diapycnal mixing, as endorsed by the elevated rates of turbulent energy dissipation e estimated from microstructure measurements. A spring–neap modulation of energy density on the MAR is found to originate from the remote generation and radiation of strong mode-1 internal tides fr...
TL;DR: A weak planetary vorticity gradient and weak density stratification in the northern North Atlantic and Nordic seas lead to time-mean currents that are strongly guided by bottom topography.
Abstract: A weak planetary vorticity gradient and weak density stratification in the northern North Atlantic and Nordic seas lead to time-mean currents that are strongly guided by bottom topography. ...