Thomas Haine | Johns Hopkins University (original) (raw)

Papers by Thomas Haine

Bulletin of the American Meteorological Society, 2021

Computational oceanography is the study of ocean phenomena by numerical simulation, especially dy... more Computational oceanography is the study of ocean phenomena by numerical simulation, especially dynamical and physical phenomena. Progress in information technology has driven exponential growth in the number of global ocean observations and the fidelity of numerical simulations of the ocean in the past few decades. The growth has been exponentially faster for ocean simulations, however. We argue that this faster growth is shifting the importance of field measurements and numerical simulations for oceanographic research. It is leading to the maturation of computational oceanography as a branch of marine science on par with observational oceanography. One implication is that ultraresolved ocean simulations are only loosely constrained by observations. Another implication is that barriers to analyzing the output of such simulations should be removed. Although some specific limits and challenges exist, many opportunities are identified for the future of computational oceanography. Most ...

Geophysical Research Letters, 2020

Mesoscale features present at the Denmark Strait sill regularly enhance the volume transport of t... more Mesoscale features present at the Denmark Strait sill regularly enhance the volume transport of the Denmark Strait overflow (DSO). They are important for the Atlantic Meridional Overturning Circulation and ultimately, for the global climate system. Using a realistic numerical model, we find new evidence of the causal relationship between overflow surges (i.e., mesoscale features associated with high-transport events) and DSO cyclones observed downstream. Most of the cyclones form at the Denmark Strait sill during overflow surges and, because of potential vorticity conservation and stretching of the water column, grow as they move equatorward. A fraction of the cyclones form downstream of the sill, when anticyclonic vortices formed during high-transport events start collapsing. Regardless of their formation mechanism, DSO cyclones weaken starting roughly 150 km downstream of the sill, and potential vorticity is only materially conserved during the growth phase. Plain Language Summary Ocean currents affecting the global climate are sustained by cold and dense water that sinks in the North Atlantic Ocean. A large portion of this water passes through Denmark Strait, the ocean channel located between Greenland and Iceland. The amount of water entering the strait varies from day to day and is controlled by ocean vortices. Knowing the mechanisms associated with these vortices is of key importance for understanding and predicting Earth's climate. Using a realistic numerical model, we find that the vortices are generated in the strait during dense water surges. In one scenario, the ocean vortices cross Denmark Strait rotating in the same direction as the Earth (counterclockwise). These vortices strengthen as they move toward the south. If the vortices initially rotate clockwise, they move slowly and quickly collapse. The water converging south of them triggers the formation of new vortices rotating counterclockwise. All of these energetic vortices move toward the equator. First they quickly grow, then they lose energy starting roughly 150 km south of Denmark Strait.

Ocean Modelling, 2017

The Denmark Strait Overflow (DSO) is a major export route for dense waters from the Nordic Seas f... more The Denmark Strait Overflow (DSO) is a major export route for dense waters from the Nordic Seas forming the lower limb of the Atlantic Meridional Overturning Circulation, an important element of the climate system. Mixing processes along the DSO pathway influence its volume transport and properties contributing to the variability of the deep overturning circulation. They are poorly sampled by observations however which hinders development of a proper DSO representation in global circulation models. We employ a high resolution regional ocean model of the Irminger Basin to quantify impact of the mesoscale flows on DSO mixing focusing on geographical localization and local time-modulation of water property changes. The model reproduces the observed bulk warming of the DSO plume 100-200 km downstream of the Denmark Strait sill. It also reveals that mesoscale variability of the overflow ('DSO-eddies', of 20-30 km extent and a time scale of 2-5 day) modulates water property changes and turbulent mixing, diagnosed with the vertical shear of horizontal velocity and the eddy heat flux divergence. The spacetime localization of the DSO mixing and warming and the role of coherent mesoscale structures should be explored by turbulence measurements and factored into the coarse circulation models.

Deep-Sea Research Part I-Oceanographic Research Papers, 2014

The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper con... more The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean's role in climate.

Quarterly Journal of the Royal Meteorological Society, 2009

This paper quantifies and discusses the impact of high-resolution, high-frequency atmospheric for... more This paper quantifies and discusses the impact of high-resolution, high-frequency atmospheric forcing on the ocean circulation in the vicinity of the Denmark Strait. The approach is to force a 2 km resolution regional ocean circulation model with atmospheric states from reanalysis products that have different spatial and temporal resolutions. We use the National Center for Environmental Prediction global reanalysis data (2.5 • resolution, 6-hourly output) and a specially configured regional atmospheric model (12 km resolution, hourly output). The focus is on the month-long period in winter 2007 during the Greenland Flow Distortion Experiment. Diagnostics of upper-ocean currents and mixing are sensitive to the small-scale variability in the high-resolution regional atmospheric model. The hydrographic state of the ocean model is insensitive over the month-long experiments, however. Both sea ice and the fluxes of volume, heat, and freshwater across the east Greenland shelf break and through the Denmark Strait show a moderate response to the high-resolution atmospheric forcing. The synoptic-scale atmospheric state has a large role in controlling sea ice too, while internal ocean dynamics is the dominant factor controlling the flux diagnostics. It is the high spatial resolution, not the temporal resolution, that causes these effects, with O(10 km)-scale features being most important. The sea-level wind field is responsible, with the other atmospheric fields playing relatively minor roles.

Quarterly Journal of the Royal Meteorological Society, 2006

This paper explores the prospects for constraining circulation and stratification estimates in th... more This paper explores the prospects for constraining circulation and stratification estimates in the Irminger Sea and Denmark Strait using variational data assimilation. A regional circulation model with 9 km horizontal grid spacing, seven vertical levels and open boundaries is used. The circulation it simulates is realistic in several important respects and includes a chaotic mesoscale eddy field. Pulsation of the outflow of dense water through the Denmark Strait is also reasonably realistic, although entrainment and mixing of this water downstream is crudely represented. Identical twin assimilation experiments are performed to address the observability of the system with the existing in situ and satellite observing network in the absence of systematic errors. That is, the constraints exerted on the circulation and stratification by the data assimilation system are quantified. Synthetic data come from a reasonably realistic observing network that includes in situ hydrographic and current measurements, and remotely sensed surface temperature and sea level. Over a 15-day assimilation period in summer, the system fits all the observations to the relevant noise level, largely by correcting the initial conditions. Only modest changes in the time-dependent surface forcing and negligible changes to the open boundary conditions are needed. The system can accurately estimate sea surface height and sea surface temperature, correcting errors in the locations of surface fronts and eddies. The mid-depth salinity is almost completely unconstrained, however, whereas the velocity fields are somewhat constrained by the assimilation, especially by the remote-sensing data. Assimilation of satellite data enables us to accurately track the phase and amplitude of the overflow variability at the exit of Denmark Strait in the identical twin experiments. At other model outflow transects the assimilated solution is contaminated with spurious inertial oscillations. This is true even at a section offshore of Angmagssalik where a current-meter mooring array exists (in our experiments and in the real ocean). Nevertheless, improvement of the model dense outflow near the moorings is significant and propagates several hundred kilometres upstream and downstream.

Ocean Modelling, 2002

Numerical studies of surface ocean fronts forced by inhomogeneous buoyancy loss show nonhydrostat... more Numerical studies of surface ocean fronts forced by inhomogeneous buoyancy loss show nonhydrostatic convective plumes coexisting with baroclinic eddies. The character of the vertical overturning depends sensitively on the treatment of the vertical momentum equation in the model. It is less well known how the frontal evolution over scales of O(10 km) is affected by these dynamics. Here, we compare highly resolved numerical experiments using nonhydrostatic and hydrostatic models and the convective-adjustment parametrization. The impact of nonhydrostatic processes on average cross-frontal transfer is weak compared to the effect of the O(1 km) scale baroclinic motions. For water-mass distribution and formation rate nonhydrostatic dynamics have similar influence to the baroclinic eddies although adequate resolution of the gradients in forcing fluxes is more important. The overall implication is that including nonhydrostatic surface frontal dynamics in ocean general circulation models will have only a minor effect on scales of O(1 km) and greater.

Nonlinear Processes in Geophysics, 2004

We report on a numerical study of the impact of short, fast inertia-gravity waves on the large-sc... more We report on a numerical study of the impact of short, fast inertia-gravity waves on the large-scale, slowlyevolving flow with which they co-exist. A nonlinear quasigeostrophic numerical model of a stratified shear flow is used to simulate, at reasonably high resolution, the evolution of a large-scale mode which grows due to baroclinic instability and equilibrates at finite amplitude. Ageostrophic inertiagravity modes are filtered out of the model by construction, but their effects on the balanced flow are incorporated using a simple stochastic parameterization of the potential vorticity anomalies which they induce. The model simulates a rotating, two-layer annulus laboratory experiment, in which we recently observed systematic inertia-gravity wave generation by an evolving, large-scale flow. We find that the impact of the small-amplitude stochastic contribution to the potential vorticity tendency, on the model balanced flow, is generally small, as expected. In certain circumstances, however, the parameterized fast waves can exert a dominant influence. In a flow which is baroclinicallyunstable to a range of zonal wavenumbers, and in which there is a close match between the growth rates of the multiple modes, the stochastic waves can strongly affect wavenumber selection. This is illustrated by a flow in which the parameterized fast modes dramatically re-partition the probabilitydensity function for equilibrated large-scale zonal wavenumber. In a second case study, the stochastic perturbations are shown to force spontaneous wavenumber transitions in the large-scale flow, which do not occur in their absence. These phenomena are due to a stochastic resonance effect. They add to the evidence that deterministic parameterizations in general circulation models, of subgrid-scale processes such as gravity wave drag, cannot always adequately capture the full details of the nonlinear interaction.

Journal of Physical Oceanography, 2005

The relationships between different tracer ages and between tracer age and potential vorticity ar... more The relationships between different tracer ages and between tracer age and potential vorticity are examined by simulating barotropic double-gyre circulations. The unsteady model flow crudely represents aspects of the midlatitude, middepth ocean circulation including inhomogeneous and anisotropic variability. Temporal variations range in scale from weeks to years, although the statistics are stationary. These variations have a large impact on the time-averaged tracer age fields. Transport properties of the tracer age fields that have been proved for steady flow are shown to also apply to unsteady flow and are illustrated in this circulation. Variability of tracer ages from ideal age tracer, linear, and exponential transient tracers is highly coordinated in phase and amplitude and is explained using simple theory. These relationships between different tracer ages are of practical benefit to the problem of interpreting tracer ages from the real ocean or from general circulation models....

Journal of Physical Oceanography, 1998

A hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the ocea... more A hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed. If a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface, then gravitational instability ensues in which buoyancy is drawn from depth by upright convection. But if spatial inhomogeneities in the ambient stratification or the forcing are present (as always exist in nature), then horizontal density gradients will be induced and, within a rotation period, horizontal currents in thermal-wind balance with those gradients will be set up within the mixed layer. There are two important consequences on the convective process: 1) Upright convection will become modified by the presence of the thermal wind shear; fluid parcels are exchanged not along vertical paths but, rather, along slanting paths in symmetric instability. Theoretical considerations suggest that this slantwise convection sets the potential vorticity of the mixed layer fluid to zero but, in general, will leave it stably stratified in the vertical. 2) The convective process ultimately gives way to a baroclinic instability of the horizontal mixed layer density gradients. The resulting baroclinic waves are important agents of buoyancy transport through the mixed layer and can be so efficient that the convective process all but ceases. The authors illustrate and quantify these ideas by numerical experiment with a highly resolved nonhydrostatic Navier-Stokes model. Uniform spatial cooling at the surface of a resting, stratified fluid in a 2½-dimensional model on an f plane, in which zonal strips of fluid conserve their absolute momentum, causes energetic vertical overturning. A well-mixed boundary layer develops over a depth that is accurately predicted by a simple 1D law. In contrast, differential surface cooling induces a mixed layer front. Fluid parcels, made dense at the surface, sink along slanting trajectories in intense nonhydrostatic plumes. After cooling ceases the Ertel potential vorticity within the convective layer is indeed found to be vanishingly small, corresponding to convective neutrality measured in the absolute momentum surfaces that are tilted from the vertical by the horizontal vorticity of the thermal wind. In analogous fully three-dimensional calculations, the absolute momentum constraint is broken, and the convection at first coexists with, but is ultimately dominated by, a baroclinic instability of the mixed layer. For typical mixed layer depths of 500 m stability analysis predicts, and our explicit calculations confirm, that baroclinic waves with length scales O(5 km) develop with timescales of a day or so. By diagnosis of fully developed mixed layer turbulence, the authors assess the importance of the baroclinic eddy field as an agency of lateral and vertical buoyancy flux through the layer. A novel scaling for the lateral buoyancy flux due to the baroclinic eddies is suggested. These ideas are based on analysis of several experiments in which the initial stratification, rotation rate, and buoyancy forcing are varied, and the results are compared to previous attempts to parameterize the effects of baroclinic instability. There is a marked difference between the scaling that accounts for the resolved experiments and the Fickian schemes used traditionally in large-scale ocean models. Finally, consideration of the results in light of high-resolution mixed layer hydrographic surveys in the northeast Atlantic suggests mixed layer baroclinic instability may be very important at fronts. The authors speculate that the process exerts a large influence on the character of newly subducted thermocline water throughout the extratropical ocean.

Journal of Physical Oceanography, 2011

Results from a high-resolution (~2 km) numerical simulation of the Irminger Basin during summer 2... more Results from a high-resolution (~2 km) numerical simulation of the Irminger Basin during summer 2003 are presented. The focus is on the East Greenland Spill Jet, a recently discovered component of the circulation in the basin. The simulation compares well with observations of surface fields, the Denmark Strait overflow (DSO), and the hydrographic structure of typical sections in the basin. The model reveals new aspects of the circulation on scales of O(0.1–10) days and O(1–100) km. The model Spill Jet results from the cascade of dense waters over the East Greenland shelf. Spilling can occur in various locations southwest of the strait, and it is present throughout the simulation but exhibits large variations on periods of O(0.1–10) days. The Spill Jet sometimes cannot be distinguished in the velocity field from surface eddies or from the DSO. The vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vo...

Journal of Physical Oceanography, 1997

Parametric representations of oceanic geostrophic eddy transfer of heat and salt are studied rang... more Parametric representations of oceanic geostrophic eddy transfer of heat and salt are studied ranging from horizontal diffusion to the more physically based approaches of Green and Stone (GS) and Gent and McWilliams (GM). The authors argue for a representation that combines the best aspects of GS and GM: transfer coefficients that vary in space and time in a manner that depends on the large-scale density fields (GS) and adoption of a transformed Eulerian mean formalism (GM). Recommendations are based upon a two-dimensional (zonally or azimuthally averaged) model with parameterized horizontal and vertical fluxes that is compared to three-dimensional numerical calculations in which the eddy transfer is resolved. Three different scenarios are considered: 1) a convective ''chimney'' where the baroclinic zone is created by differential surface cooling; 2) spindown of a frontal zone due to baroclinic eddies; and 3) a wind-driven, baroclinically unstable channel. Guided by baroclinic instability theory and calibrated against eddy-resolving calculations, the authors recommend a form for the horizontal transfer coefficient given by 2 f M 2 2 kϭ␣ l ϭ␣ l , N ͙Ri where Ri ϭ f 2 N 2 /M 4 is the large-scale Richardson number and f is the Coriolis parameter; M 2 and N 2 are measures of the horizontal and vertical stratification of the large-scale flow, l measures the width of the baroclinic zone, and ␣ is a constant of proportionality. In the very different scenarios studied here the authors find ␣ to be a ''universal'' constant equal to 0.015, not dissimilar to that found by Green for geostrophic eddies in the atmosphere. The magnitude of the implied k, however, varies from 300 m 2 s Ϫ1 in the chimney to 2000 m 2 s Ϫ1 in the wind-driven channel. * Contribution Number 5496 from Lamont-Doherty Earth Observatory and Contribution Number 9154 from Woods Hole Oceanographic Institution.

Journal of Physical Oceanography, 2013

The Denmark Strait Overflow (DSO) supplies about one-third of the North Atlantic Deep Water and i... more The Denmark Strait Overflow (DSO) supplies about one-third of the North Atlantic Deep Water and is critical to global thermohaline circulation. Knowledge of the pathways of DSO through the Irminger Basin and its transformation there is still incomplete, however. The authors deploy over 10 000 Lagrangian particles at the Denmark Strait in a high-resolution ocean model to study these issues. First, the particle trajectories show that the mean position and potential density of dense waters cascading over the Denmark Strait sill evolve consistently with hydrographic observations. These sill particles transit the Irminger Basin to the Spill Jet section (65.25°N) in 5–7 days and to the Angmagssalik section (63.5°N) in 2–3 weeks. Second, the dense water pathways on the continental shelf are consistent with observations and particles released on the shelf in the strait constitute a significant fraction of the dense water particles recorded at the Angmagssalik section within 60 days (~25%). ...

Journal of Geophysical Research, 2008

Chlorofluorocarbons (CFCs) enter the middepth layers of the North Atlantic Ocean from the atmosph... more Chlorofluorocarbons (CFCs) enter the middepth layers of the North Atlantic Ocean from the atmosphere during the formation of dense mode water in the Labrador and Irminger Seas of the subpolar gyre. The CFC-bearing waters then spread from the convection regions through advection and diffusion of the water masses. Using recent estimates of the circulation at 1500 m depth from subsurface profiling floats the spreading of CFC-11 is simulated in the subpolar North Atlantic with an advective-diffusive model. Several numerical experiments are performed with different stream functions, lateral diffusivities and variations in the CFC-11 sources. The results are then compared to the observed CFC-11 field during 1996-1998. Poor fits are found for diffusivities less than about 500 m 2 s À1. Better fits are found for diffusivities ranging from 500-12,000 m 2 s À1 , although unrealistically smooth model solutions are produced if the diffusivity exceeds about 3000 m 2 s À1. Simulations that include both Labrador and Irminger Sea CFC-11 sources fit the data better than with Labrador sources alone. None of the model CFC solutions fit the data within the CFC uncertainty over the whole domain; the model performs well in the western part of the subpolar gyre, but CFC-11 concentrations are consistently too low in the West European Basin. It is possible that uncertainty in the floatbased circulation can account for these misfits, and a more accurate circulation estimate might be able to fit the observed CFC-11 field. Alternatively, time variations in the flow or deep water formation processes, which clearly exist in the real ocean, may need to be included.

Journal of Fluid Mechanics, 2005

We report on the results of a laboratory investigation using a rotating two-layer annulus experim... more We report on the results of a laboratory investigation using a rotating two-layer annulus experiment, which exhibits both large-scale vortical modes and short-scale divergent modes. A sophisticated visualization method allows us to observe the flow at very high spatial and temporal resolution. The balanced long-wavelength modes appear only when the Froude number is supercritical (i.e. F > F critical ≡ π 2 /2), and are therefore consistent with generation by a baroclinic instability. The unbalanced shortwavelength modes appear locally in every single baroclinically unstable flow, providing perhaps the first direct experimental evidence that all evolving vortical flows will tend to emit freely propagating inertia-gravity waves. The short-wavelength modes also appear in certain baroclinically stable flows. We infer the generation mechanisms of the short-scale waves, both for the baroclinically unstable case in which they co-exist with a large-scale wave, and for the baroclinically stable case in which they exist alone. The two possible mechanisms considered are spontaneous adjustment of the large-scale flow, and Kelvin-Helmholtz shear instability. Short modes in the baroclinically stable regime are generated only when the Richardson number is subcritical (i.e. Ri < Ri critical ≡ 1), and are therefore consistent with generation by a Kelvin-Helmholtz instability. We calculate five indicators of shortwave generation in the baroclinically unstable regime, using data from a quasi-geostrophic numerical model of the annulus. There is excellent agreement between the spatial locations of shortwave emission observed in the laboratory, and regions in which the model Lighthill/Ford inertia-gravity wave source term is large. We infer that the short waves in the baroclinically unstable fluid are freely propagating inertia-gravity waves generated by spontaneous adjustment of the large-scale flow.

Geoscientific Model Development, 2009

Geophysical Research Letters, 2003

Inertia-gravity waves exist ubiquitously throughout the stratified parts of the atmosphere and oc... more Inertia-gravity waves exist ubiquitously throughout the stratified parts of the atmosphere and ocean. They are generated by local velocity shears, interactions with topography, and as geostrophic (or spontaneous) adjustment radiation. Relatively little is known about the details of their interaction with the large-scale flow, however. We report on a joint model/laboratory study of a flow in which inertia-gravity waves are generated as spontaneous adjustment radiation by an evolving largescale mode. We show that their subsequent impact upon the large-scale dynamics is generally small. However, near a potential transition from one large-scale mode to another, in a flow which is simultaneously baroclinically-unstable to more than one mode, the inertia-gravity waves may strongly influence the selection of the mode which actually occurs.

Environmental Fluid Mechanics, 2010

Understanding advective-diffusive transport of trace constituents in natural fluid flows is an im... more Understanding advective-diffusive transport of trace constituents in natural fluid flows is an important challenge in Earth and environmental sciences with many diverse applications, including simulating the fate of contaminants, inferring the location of their source, and model assessment (e.g., [7,21]). Eulerian and Lagrangian methods are routinely used, including novel representations of mixing processes that resort to the so-called fractional-order diffusion. Moreover, geophysical and environmental fluid-flow models routinely produce huge amounts of output, and to make sense of these results sophisticated interpretation methods are required. Among these methods, an approach that is becoming progressively more popular consists in using real, or hypothetical, tracers to tag fluid masses and estimate associated timescales, such as age, residence time, and transit time. These timescales lead to very useful diagnoses that are increasingly applied in interdisciplinary environmental studies (e.g. [2,5]). This special issue presents a number of studies that are relevant to the above-mentioned field of research. Groundwater, soil water, riverine, estuarine, marine and ocean flows are considered, as well as the transport of sinking particles in water.