Joseph Henry Lacasce

• Johnston, T. M.Shaun & Lacasce, Joseph Henry (2026). Horizontal Eddy Diffusivities and Heat Fluxes in the Norwegian Sea From Argo. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 131(5). doi: 10.1029/2025JC023877. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry; Hajduk, Hennes & Brændshøi, Jostein (2026). Unstable Rossby waves over bathymetry. Journal of Fluid Mechanics. ISSN 0022-1120. 1034. doi: 10.1017/jfm.2026.11482. Fulltekst i vitenarkiv Vis sammendrag

  The instability of baroclinic Rossby waves over two-dimensional topography is examined using a nonlinear model, a linear stability calculation and wave triads. In all cases, the Rossby waves are unstable, as seen previously over a flat bottom. But topography decreases the growth rates and changes the structure of the unstable waves. When the topographic height (or slope) exceeds a critical value, the instability is ‘locked’ to topography, in that the most unstable mode, particularly in the lower layer, resembles the bathymetry. In this limit, the growth rate becomes independent of topographic height. A triad calculation suggests that the growth rates in the locked state should depend on the lateral scale of the bathymetry but not its height, and that locking does not occur for topographic scales smaller than the surface deformation radius. The results suggest an alternate way that topographically locked flow can be generated, and indicate that baroclinic instability can be much different over steep bathymetry.

• Qian, Yu Kun; Lacasce, Joseph Henry & Peng, Shiqiu (2025). Inferring Submesoscale Energy Spectra in the Gulf of Mexico from Surface Drifters. Journal of Physical Oceanography. ISSN 0022-3670. 55(9), s. 1475–1491. doi: 10.1175/JPO-D-24-0258.1. Fulltekst i vitenarkiv Vis sammendrag

  Calculating energy spectra in the ocean is impeded by the resolution limitations of satellite and shipboard acoustic Doppler current profiler (ADCP) data. An alternate approach is to use data from GPS-tracked surface drifters, which offer resolution to finer than 10 m. While direct spectral estimates from drifter velocities have been unsuccessful, indirect estimates, based on the dispersion of pairs of drifters, are possible. Using drifter data from the Gulf of Mexico, we infer wavenumber spectra by comparing pair dispersion to that expected with different spectral slopes. The measures include both time- and separation-based metrics and establish consistency between the two using the recently proposed cumulative inverse separation time (CIST), a separation-based measure similar to the finite-scale Lyapunov exponent (FSLE). The results indicate a K−2 dependence from 100 m to several kilometers. The spectral slope is the same up to the deformation radius (∼50 km) in winter, while in summer, it is steeper, close to a K−3 dependence. Additional separation-based metrics suggest a shallower K−5/3 spectrum in the 10–100-m range, but this cannot be confirmed with the time-based metrics. The results are consistent with previous drifter studies and help resolve differences between them. Differences between “original” and “chance” pairs are seen at the smallest scales (<1 km), where the dispersion is affected by the initial conditions. Furthermore, the FSLE fails to capture the smallest-scale dispersion, while a modified version, the finite amplitude growth rate (FAGR), is more successful. The findings will help guide future studies of submesoscale dispersion.

• Roquet, Fabien; Bell, Michael J.; Boer, Agatha M. de; Ferreira, David; Jones, C. Spencer & Lacasce, Joseph Henry [Vis alle 11 forfattere av denne artikkelen] (2025). Controls of the global overturning circulation of the ocean. npj Climate and Atmospheric Science. 8(1). doi: 10.1038/s41612-025-01185-8. Fulltekst i vitenarkiv Vis sammendrag

  The global overturning circulation (GOC) is the largest scale component of the ocean circulation, associated with a global redistribution of key tracers such as heat and carbon. The GOC generates decadal to millennial climate variability, and will determine much of the long-term response to anthropogenic climate perturbations. This review aims at providing an overview of the main controls of the GOC. By controls, we mean processes affecting the overturning structure and variability. We distinguish three main controls: mechanical mixing, convection, and wind pumping. Geography provides an additional control on geological timescales. An important emphasis of this review is to present how the different controls interact with each other to produce an overturning flow, making this review relevant to the study of past, present and future climates as well as to exoplanets’ oceans.

• Sjur, Anna Lina Petruseviciute; Isachsen, Pål Erik; Johan, Nilsson; Lacasce, Joseph Henry & Ryseth, Magnus Dyrmose (2025). The Wind-Driven Time-Variable Circulation in the Arctic Mediterranean. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 130(4), s. 1–20. doi: 10.1029/2024JC021713. Fulltekst i vitenarkiv Vis sammendrag

  The Arctic Ocean is a key component of Earth's climate system, and an understanding of ocean dynamics in this region is central for predicting how the Arctic is responding to a changing climate. In this study, we examine the ocean circulation in a high-resolution numerical model of the Arctic Ocean and Nordic Seas. Based on what is observed in this simulation, we reexamine an existing idealized linear model estimating the time-variable large-scale circulation in ocean basins, and test it against the highly nonlinear numerical model. The idealized model is an integral relation derived from the linear momentum equations and assumes that the circulation around a closed depth contour is driven by surface stresses and regulated by bottom friction. We show that the idealized model estimates agree very well with the numerical simulations. This indicates that much of the variability of the large-scale circulation can be explained by linear processes. In particular, a correct description of the net surface stress over partially ice-covered areas improves the correlation between linear model and numerical simulations significantly in the Arctic Ocean compared to a previous study. However, undetected in that previous study, we now find that the linear model might be lacking a cyclonic tendency.

• Sterl, Miriam F.; Palóczy, André; Groeskamp, Sjoerd; Baatsen, Michiel; Lacasce, Joseph Henry & Isachsen, Pål Erik (2025). The joint effects of planetary β, topography and friction on baroclinic instability in a two-layer QG model. Journal of Fluid Mechanics. ISSN 0022-1120. 1012. doi: 10.1017/jfm.2025.10172. Fulltekst i vitenarkiv Vis sammendrag

  The quasi-geostrophic two-layer model is a widely used tool to study baroclinic instability in the ocean. One instability criterion for the inviscid two-layer model is that the potential vorticity (PV) gradient must change sign between the layers. This has a well-known implication if the model includes a linear bottom slope: for sufficiently steep retrograde slopes, instability is suppressed for a flow parallel to the isobaths. This changes in the presence of bottom friction as well as when the PV gradients in the layers are not aligned. We derive the generalised instability condition for the two-layer model with non-zero friction and arbitrary mean flow orientation. This condition involves neither the friction coefficient nor the bottom slope; even infinitesimally weak bottom friction destabilises the system regardless of the bottom slope. We then examine the instability characteristics as a function of varying slope orientation and magnitude. The system is stable across all wavenumbers only if friction is absent and if the planetary, topographic and stretching PV gradients are aligned. Strong bottom friction decreases the growth rates but also alters the dependence on bottom slope. In conclusion, the often mentioned stabilisation by steep bottom slopes in the two-layer model holds only in very specific circumstances, thus probably plays only a limited role in the ocean.

• Johnston, Shaun; Sjur, Anna Lina Petruseviciute; Isachsen, Pål Erik & Lacasce, Joseph Henry (2025). Eddy- and wind-driven circulation in the enclosed basins of the Norwegian Sea evaluated using a model and absolute geostrophic flow from Argo. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 130(7). doi: 10.1029/2024JC021990. Fulltekst i vitenarkiv Vis sammendrag

  Cyclonic flow in enclosed basins arises from cyclonic vorticity input from either winds or eddies. Previous observations show winds account for about half of the circulation (integral of parallel velocity around a closed isobath) in the Lofoten Basin of the Norwegian Sea, implying a comparable contribution from eddies. In contrast, in the Norwegian Basin, winds explain much of the circulation. We use Argo data from 2012 to 2022, a linear wind-forced and bottom friction-regulated model, and a primitive equation model to investigate how winds and eddies drive the circulation. While Argo cannot resolve individual eddies, it does resolve mesoscale spatial variability. Absolute geostrophic velocities to 2,000 m are calculated by referencing geostrophic shear from objective maps of the profile data to the trajectories at 1,000 m. The time-mean shear is anticyclonic. However, the flow is mostly cyclonic, bottom-intensified, and isobath following. The linear model explains less than half of the observed circulation, suggesting a contribution from an unobserved eddy flux. This interpretation is supported by a numerical model with 800-m horizontal resolution, which resolves the 10–15-km deformation radius. In this model, the difference between the full and linear response comes from an eddy-driven vorticity flux, which produces a largely cyclonic circulation. This result is consistent with the observed global prevalence of positive topostrophy (anticyclonic flow around elevations and cyclonic flow around basins). The observations also show a seasonal shift in the eddy flux, which maybe related to a decadal-scale fresh inflow that alters the density gradient and influences eddy production.

• Sterl, Miriam F.; Lacasce, Joseph Henry; Groeskamp, Sjoerd; Nummelin, Aleksi Henrynpoika; Isachsen, Pål Erik & Baatsen, Michiel L. J. (2024). Suppression of Mesoscale Eddy Mixing by Topographic PV Gradients. Journal of Physical Oceanography. ISSN 0022-3670. 54(5), s. 1089–1103. doi: 10.1175/JPO-D-23-0142.1. Fulltekst i vitenarkiv Vis sammendrag

  Oceanic mesoscale eddy mixing plays a crucial role in Earth’s climate system by redistributing heat, salt, and carbon. For many ocean and climate models, mesoscale eddies still need to be parameterized. This is often done via an eddy diffusivity K , which sets the strength of turbulent downgradient tracer fluxes. A well-known effect is the modulation of K in the presence of background potential vorticity (PV) gradients, which suppresses mixing in the direction of the PV gradients. Topographic slopes can induce such suppression through topographic PV gradients. However, this effect has received little attention, and topographic effects are often not included in parameterizations for K . In this study, we show that it is possible to describe the effect of topography on K analytically in a barotropic framework, using a simple stochastic representation of eddy–eddy interactions. We obtain an analytical expression for the depth-averaged K as a function of the bottom slope, which we validate against diagnos

• Lacasce, Joseph Henry; Filho, André Paloczy & Trodahl, Marta (2024). Vortices over bathymetry. Journal of Fluid Mechanics. ISSN 0022-1120. 979. doi: 10.1017/jfm.2023.1084. Fulltekst i vitenarkiv Vis sammendrag

  There are numerous examples of long-lived, surface-intensified anticyclones over submarine depressions and troughs in the ocean. These often co-exist with a large-scale cyclonic circulation. The latter is predicted by existing barotropic theory but the anticyclone is not. We extend one such theory, which minimizes enstrophy while conserving energy, to two fluid layers. This yields a bottom-intensified flow with cyclonic circulation over a depression. The solution is steady, an enstrophy minimum and stable. When the Lagrange multiplier, λ, is near zero, the total potential vorticity (PV) becomes homogenized, in both layers. For positive λ, the surface PV is anticyclonic and strongest at intermediate energies. In quasi-geostrophic numerical simulations with a random initial perturbation PV, the bottom-intensified cyclonic flow always emerges. Vortices evolve independently in the layers and vortex mergers are asymmetric over the depression; cyclones are preferentially strained out at depth while only anticyclones merge at the surface. Both asymmetries are linked to the topographic flow. The deep cyclones feed the bottom-intensified cyclonic circulation while the asymmetry at the surface is only apparent after that circulation has spun up. The result of the surface merger asymmetry is often a lone anticyclone above the depression. This occurs primarily at intermediate energies, when the surface PV predicted by the theory is strongest. Similar results obtain in a full complexity ocean model but with a more pronounced asymmetry in surface vortex mergers and, with bottom friction, significant bottom flow beneath the central anticyclone.

• Madan, Gaurav; Gjermundsen, Ada; Iversen, Silje Christine & Lacasce, Joseph Henry (2023). The weakening AMOC under extreme climate change. Climate Dynamics. ISSN 0930-7575. 62, s. 1291–1309. doi: 10.1007/s00382-023-06957-7. Fulltekst i vitenarkiv Vis sammendrag

  Changes in the Atlantic Meridional Overturning Circulation (AMOC) in the quadrupled CO₂ experiments conducted under the sixth Coupled Model Intercomparison Project (CMIP6) are examined. Increased CO₂ triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, frst from the Labrador Sea and then the Nordic Seas, and proceeds along the eastern coast of North America. The freshwater enters the subpolar gyre north of the separated Gulf Stream, the North Atlantic Current. This decreases the density gradient across the current and the current weakens in response, reducing the infow to the deepwater production regions. The AMOC cell weakens in tandem, frst near the North Atlantic Current and then spreading to higher and lower latitudes. This contrasts with the common perception that freshwater caps the convection regions, stifing deepwater production; rather, it is the infow to the subpolar gyre that is suppressed. Changes in surface temperature have a much weaker effect, and there are no consistent changes in local or remote wind forcing among the models. Thus an increase in freshwater discharge, primarily from the Labrador Sea, is the precursor to AMOC weakening in these simulations.

• Filho, André Paloczy & Lacasce, Joseph Henry (2023). Prevalence of Deformation-Scale Surface Currents. Geophysical Research Letters. ISSN 0094-8276. 50(21). doi: 10.1029/2023GL104547. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Understanding the transport of large ocean currents, like the Gulf Stream, has been of interest since the early days of oceanography. There has been less attention on the widths of the currents, although there exist several theoretical predictions. We present a census of time‐averaged jet profiles, using in situ and satellite data. The jets are typically asymmetrical, being narrower on the side with weaker stratification. The half‐widths L j are correlated with the local deformation radius L d associated with the first surface mode on either side. The dependence of L j on L d is predicted by simple shallow water geostrophic adjustment models, with or without outcropping layers. This implies that potential vorticity is well‐mixed adjacent to the jets, due most likely to mesoscale eddies. The findings suggest that surface jet widths are determined locally, by eddy‐mean flow interactions.

• Brown, Nicola; Mauritzen, Cecilie; Li, Camille; Madonna, Erica; Isachsen, Pål Erik & Lacasce, Joseph Henry (2023). Rapid Response of the Norwegian Atlantic Slope Current to Wind Forcing. Journal of Physical Oceanography. ISSN 0022-3670. 53(2), s. 389–408. doi: 10.1175/JPO-D-22-0014.1. Fulltekst i vitenarkiv Vis sammendrag

  We explore drivers of variability in the Norwegian Atlantic Slope Current, which carries relatively warm Atlantic Water toward the Barents Sea and Arctic Ocean, using Copernicus Marine Environment Monitoring Service (CMEMS) satellite altimetry data and TOPAZ4 ocean reanalysis data. Previous studies have pointed to a variety of causes, on a variety of time scales. We use data with daily resolution to investigate day-to-day changes in ocean transport across three sections crossing the shelf-slope of Norway (Svinøy, Gimsøy, and the Barents Sea Opening). The highest (lowest) extremes in transport at all sections develop over two days as a cyclonic (anticyclonic) atmospheric pressure system approaches from the southwest, piling up (extracting) water at the coast of Norway. The actual peak is reached when the pressure system passes the site of measurement, and the transport then relaxes for the next two days as the system continues northward along the coast. Other sources of short-term variability, such as propagating continental shelf waves and baroclinic instability, are unlikely to yield covariability over large separations. Monthly variability in the current can also be explained by passing weather systems since their numbers and intensity vary greatly from month to month. Many studies of longer-term variability, especially in the Barents Sea Opening, have pointed to the North Atlantic Oscillation (NAO) as the main cause of variability. Our results show that passing weather systems offer a better explanation of month-to-month variability.

• Klocker, Andreas; Munday, David; Gayen, Bishakhdatta; Roquet, Fabien & Lacasce, Joseph Henry (2023). Deep-Reaching Global Ocean Overturning Circulation Generated by Surface Buoyancy Forcing. Tellus A: Dynamic Meteorology and Oceanography. ISSN 0280-6495. 75(1), s. 392–409. doi: 10.16993/tellusa.3231. Fulltekst i vitenarkiv Vis sammendrag

  In contrast with the atmosphere, which is heated from below by solar radiation, the ocean is both heated and cooled from above. To drive a deep-reaching overturning circulation in this context, it is generally assumed that either intense interior mixing by winds and internal tides, or wind-driven upwelling is required; in their absence, the circulation is thought to collapse to a shallow surface cell. We demonstrate, using a primitive equation model with an idealized domain and no wind forcing, that the surface temperature forcing can in fact drive an interhemispheric overturning provided that there is an open channel unblocked in the zonal direction, such as in the Southern Ocean. With this geometry, rotating horizontal convection, in combination with asymmetric surface cooling between the north and south, drives a deep-reaching two-cell overturning circulation. The resulting vertical mid-depth stratification closely resembles that of the real ocean, suggesting that wind-driven pumping is not necessary to produce a deep-reaching overturning circulation, and that buoyancy forcing plays a more important role than is usually assumed.

• Ni, Qinbiao; Zhai, Xiaoming; Lacasce, Joseph Henry; Chen, Dake & Marshall, David P. (2023). Full-Depth Eddy Kinetic Energy in the Global Ocean Estimated From Altimeter and Argo Observations. Geophysical Research Letters. ISSN 0094-8276. 50(15). doi: 10.1029/2023GL103114. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Although the surface eddy kinetic energy (EKE) has been well studied using satellite altimeter and surface drifter observations, our knowledge of EKE in the ocean interior is much more limited due to the sparsity of subsurface current measurements. Here we develop a new approach for estimating EKE over the full depth of the global ocean by combining 20 years of satellite altimeter and Argo float data to infer the vertical profile of eddies. The inferred eddy profiles are surface‐intensified at low latitudes and deep‐reaching at mid‐ and high latitudes. They compare favorably to the first empirical orthogonal function obtained from current meter velocities. The global‐integrated EKE estimated from the inferred profiles is about 3.1 × 10 18  J, which is close to that estimated from the surface mode (3.0 × 10 18  J) but about 30% smaller than that estimated from the traditional flat bottom modes (4.6 × 10 18  J).

• Hochmuth, Katharina; Whittaker, Joanne M.; Sauermilch, Isabel; Klocker, Andreas; Gohl, Karsten & LaCasce, Joseph H. (2022). Southern Ocean biogenic blooms freezing-in Oligocene colder climates. Nature Communications. 13. doi: 10.1038/s41467-022-34623-9. Fulltekst i vitenarkiv Vis sammendrag

  Crossing a key atmospheric CO2 threshold triggered a fundamental global climate reorganisation ~34 million years ago (Ma) establishing permanent Antarctic ice sheets. Curiously, a more dramatic CO2 decline (~800–400 ppm by the Early Oligocene(~27 Ma)), postdates initial ice sheet expansion but the mechanisms driving this later, rapid drop in atmospheric carbon during the early Oligocene remains elusive and controversial. Here we use marine seismic reflection and borehole data to reveal an unprecedented accumulation of early Oligocene strata (up to 2.2 km thick over 1500 × 500 km) with a major biogenic component in the Australian Southern Ocean. High-resolution ocean simulations demonstrate that a tectonically-driven, one-off reorganisation of ocean currents, caused a unique period where current instability coincided with high nutrient input from the Antarctic continent. This unrepeated and short-lived environment favoured extreme bioproductivity and enhanced sediment burial. The size and rapid accumulation of this sediment package potentially holds ~1.067 × 1015 kg of the ‘missing carbon’ sequestered during the decline from an Eocene high CO2-world to a mid-Oligocene medium CO2-world, highlighting the exceptional role of the Southern Ocean in modulating long-term climate.

• Filho, André Paloczy & Lacasce, Joseph Henry (2022). Instability of a Surface Jet over Rough Topography. Journal of Physical Oceanography. ISSN 0022-3670. 52(11), s. 2725–2740. doi: 10.1175/JPO-D-22-0079.1. Fulltekst i vitenarkiv
• Rodal, Marie; Krumscheid, Sebastian; Madan, Gaurav; Lacasce, Joseph Henry & Vercauteren, Nikki (2022). Dynamical stability indicator based on autoregressive moving-average models: Critical transitions and the Atlantic meridional overturning circulation. Chaos. ISSN 1054-1500. 32(11). doi: 10.1063/5.0089694. Fulltekst i vitenarkiv Vis sammendrag

  A statistical indicator for dynamic stability, known as the [Formula: see text] indicator, is used to gauge the stability and, hence, detect approaching tipping points of simulation data from a reduced five-box model of the North Atlantic Meridional Overturning Circulation (AMOC) exposed to a time-dependent hosing function. The hosing function simulates the influx of fresh water due to the melting of the Greenland ice sheet and increased precipitation in the North Atlantic. The [Formula: see text] indicator is designed to detect changes in the memory properties of the dynamics and is based on fitting auto-regressive moving-average models in a sliding window approach to time series data. An increase in memory properties is interpreted as a sign of dynamical instability. The performance of the indicator is tested on time series subject to different types of tipping, namely, bifurcation-induced, noise-induced, and rate-induced tipping. The numerical analysis shows that the indicator indeed responds to the different types of induced instabilities. Finally, the indicator is applied to two AMOC time series from a full complexity Earth systems model (CESM2). Compared with the doubling [Formula: see text] scenario, the quadrupling [Formula: see text] scenario results in stronger dynamical instability of the AMOC during its weakening phase.

• Lacasce, Joseph Henry & Meunier, Thomas (2022). Relative dispersion with finite inertial ranges. Journal of Fluid Mechanics. ISSN 0022-1120. 932. doi: 10.1017/jfm.2021.1050. Fulltekst i vitenarkiv
• Meunier, Thomas & Lacasce, Joseph Henry (2021). The finite size lyapunov exponent and the finite amplitude growth rate. Fluids. 6(10). doi: 10.3390/fluids6100348. Fulltekst i vitenarkiv Vis sammendrag

  The finite size Lyapunov exponent (FSLE) has been used extensively since the late 1990s to diagnose turbulent regimes from Lagrangian experiments and to detect Lagrangian coherent structures in geophysical flows and two-dimensional turbulence. Historically, the FSLE was defined in terms of its computational method rather than via a mathematical formulation, and the behavior of the FSLE in the turbulent inertial ranges is based primarily on scaling arguments. Here, we propose an exact definition of the FSLE based on conditional averaging of the finite amplitude growth rate (FAGR) of the particle pair separation. With this new definition, we show that the FSLE is a close proxy for the inverse structural time, a concept introduced a decade before the FSLE. The (in)dependence of the FSLE on initial conditions is also discussed, as well as the links between the FAGR and other relevant Lagrangian metrics, such as the finite time Lyapunov exponent and the second-order velocity structure function.

• Sauermilch, Isabel; Whittaker, Joanne M.; Klocker, Andreas; Munday, David R.; Hochmuth, Katharina & Bijl, Peter K. [Vis alle 7 forfattere av denne artikkelen] (2021). Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling. Nature Communications. 12, s. 1–8. doi: 10.1038/s41467-021-26658-1. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Declining atmospheric CO 2 concentrations are considered the primary driver for the Cenozoic Greenhouse-Icehouse transition, ~34 million years ago. A role for tectonically opening Southern Ocean gateways, initiating the onset of a thermally isolating Antarctic Circumpolar Current, has been disputed as ocean models have not reproduced expected heat transport to the Antarctic coast. Here we use high-resolution ocean simulations with detailed paleobathymetry to demonstrate that tectonics did play a fundamental role in reorganising Southern Ocean circulation patterns and heat transport, consistent with available proxy data. When at least one gateway (Tasmanian or Drake) is shallow (300 m), gyres transport warm waters towards Antarctica. When the second gateway subsides below 300 m, these gyres weaken and cause a dramatic cooling (average of 2–4 °C, up to 5 °C) of Antarctic surface waters whilst the ACC remains weak. Our results demonstrate that tectonic changes are crucial for Southern Ocean climate change and should be carefully considered in constraining long-term climate sensitivity to CO 2 .

• Röhrs, Johannes; Sutherland, Graig; Jeans, Gus; Bedington, Michael; Sperrevik, Ann Kristin & Dagestad, Knut-Frode [Vis alle 10 forfattere av denne artikkelen] (2021). Surface currents in operational oceanography: Key applications, mechanisms, and methods. Journal of operational oceanography. Publisher: The Institute of Marine Engineering, Science & Technology. ISSN 1755-876X. doi: 10.1080/1755876X.2021.1903221. Fulltekst i vitenarkiv Vis sammendrag

  This paper reviews physical mechanisms, observation techniques and modelling approaches dealing with surface currents on short time scales (hours to days) relevant for operational oceanography. Key motivations for this article include fundamental difficulties in reliable measurements and the persistent lack of a widely held consensus on the definition of surface currents. These problems are augmented by the fact that various methods to observe and model ocean currents yield very different representations of a surface current. We distinguish between four applicable definitions for surface currents; (i) the interfacial surface current, (ii) the direct wind-driven surface current, (iii) the surface boundary layer current, and (iv) an effective drift current. Finally, we discuss challenges in synthesising various data sources of surface currents - i.e. observational and modelling – and take a view on the predictability of surface currents concluding with arguments that parts of the surface circulation exhibit predictability useful in an operational context.

• Lacasce, Joseph Henry & Groeskamp, Sjoerd (2020). Baroclinic modes over rough bathymetry and the surface deformation radius. Journal of Physical Oceanography. ISSN 0022-3670. 50(10), s. 2835–2847. doi: 10.1175/JPO-D-20-0055.1. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The deformation radius is widely used as an indication of the eddy length scale at different latitudes. The radius is usually calculated assuming a flat ocean bottom. However, bathymetry alters the baroclinic modes and hence their deformation radii. In a linear quasigeostrophic two-layer model with realistic parameters, the deep flow for a 100-km wave approaches zero with a bottom ridge roughly 10 m high, leaving a baroclinic mode that is mostly surface trapped. This is in line with published current meter studies showing a primary EOF that is surface intensified and has nearly zero flow at the bottom. The deformation radius associated with this “surface mode” is significantly larger than that of the flat bottom baroclinic mode. Using World Ocean Atlas data, the surface radius is found to be 20%–50% larger over much of the globe, and 100% larger in some regions. This in turn alters the long Rossby wave speed, which is shown to be 1.5–2 times faster than over a flat bottom. In addition, the larger deformation radius is easier to resolve in ocean models.

• Groeskamp, Sjoerd; Lacasce, Joseph Henry; McDougall, Trevor J. & Rogé, Marine (2020). Full‐Depth Global Estimates of Ocean Mesoscale Eddy Mixing From Observations and Theory. Geophysical Research Letters. ISSN 0094-8276. 47(18). doi: 10.1029/2020GL089425. Fulltekst i vitenarkiv Vis sammendrag

  Mixing by mesoscale eddies profoundly impacts climate and ecosystems by redistributing and storing dissolved tracers such as heat and carbon. Eddy mixing is parameterized in most numerical models of the ocean and climate. To reduce known sensitivity to such parameterizations, observational estimates of mixing are needed. However, logistical and technological limitations obstruct our ability to measure global time‐varying mixing rates. Here, we extend mixing length theory with mean‐flow suppression theory, and first surface modes, to estimate mixing from readily available observational‐based climatological data, of salinity, temperature, pressure, and eddy kinetic energy at the sea surface. The resulting full‐depth global maps of eddy mixing can reproduce the few available direct estimates and confirm the importance of mean‐flow suppression of mixing. The results also emphasize the significant effect of eddy surface intensification and its relation to the vertical density stratification. These new insights in mixing dynamics will improve future mesoscale eddy mixing parameterizations.

• Vollestad, Petter; Ayati, Anis Awal; Angheluta, Luiza; Lacasce, Joseph Henry & Jensen, Atle (2019). Experimental investigation of airflow above waves in a horizontal pipe. International Journal of Multiphase Flow. ISSN 0301-9322. 110, s. 37–49. doi: 10.1016/j.ijmultiphaseflow.2018.08.008. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the effect of waves on the airflow in horizontal two-phase pipe flow. Velocity fields in the gaseous phase were acquired by particle image velocimetry (PIV), while interfacial elevation was measured with conductance wave probes. The velocity fields were sampled on a wave-following coordinate system which allows for a decomposition of the velocity field into a mean, wave-coherent and fluctuating component by means of a three-component Reynolds decomposition. Additionally, coherent vortical structures were identified by the swirling strength criterion, and their distribution along the waves is investigated. Results suggest that the interaction between turbulent airflow and propagating waves in a pipe has a number of features reminiscent of wind-wave interaction in open systems. Above waves generated by sufficiently high gas flow rates, there is a distinct region of sheltered airflow, and a lifting of the critical layer on the leeward side of the crest. Streamlines of the phase-averaged flow field show a cat’s eye structure located close to the crest in this region. Above waves of moderate steepness, we observe a shear layer that remains adjacent to the wave surface. Above steeper waves and higher gas flow rate, this layer detaches from the surface just downstream of the crest. Shear layer separation above waves is traditionally linked to the onset of wave breaking, and it is interesting to note that the case where we observe a separated shear layer in the phase-averaged vorticity field is in a regime of amplitude saturation. The swirling strength criterion reveals that vortical structures are shed from the interface and populate the detached shear layer above the trough. Below the detached shear layer, there is a region populated by counter-rotating vortices. The critical height coincides with the border between these two regions.

• Lacasce, Joseph Henry; Escartin, Javier; Chassignet, Eric P. & Xu, Xiaobiao (2019). Jet Instability over Smooth, Corrugated, and Realistic Bathymetry. Journal of Physical Oceanography. ISSN 0022-3670. 49(2), s. 585–605. doi: 10.1175/JPO-D-18-0129.1. Fulltekst i vitenarkiv Vis sammendrag

  The stability of a horizontally and vertically sheared surface jet is examined, with a focus on the vertical structure of the resultant eddies. Over a flat bottom, the instability is mixed baroclinic/barotropic, producing strong eddies at depth that are characteristically shifted downstream relative to the surface eddies. Baroclinic instability is suppressed over a large slope for retrograde jets (with a flow antiparallel to topographic wave propagation) and to a lesser extent for prograde jets (with flow parallel to topographic wave propagation), as seen previously. In such cases, barotropic (lateral) instability dominates if the jet is sufficiently narrow. This yields surface eddies whose size is independent of the slope but proportional to the jet width. Deep eddies still form, forced by interfacial motion associated with the surface eddies, but they are weaker than under baroclinic instability and are vertically aligned with the surface eddies. A sinusoidal ridge acts similarly, suppressing baroclinic instability and favoring lateral instability in the upper layer. A ridge with a 1-km wavelength and an amplitude of roughly 10 m is sufficient to suppress baroclinic instability. Surveys of bottom roughness from bathymetry acquired with shipboard multibeam echo sounding reveal that such heights are common beneath the Kuroshio, the Antarctic Circumpolar Current, and, to a lesser extent, the Gulf Stream. Consistent with this, vorticity and velocity cross sections from a 1/50° HYCOM simulation suggest that Gulf Stream eddies are vertically aligned, as in the linear stability calculations with strong topography. Thus, lateral instability may be more common than previously thought, owing to topography hindering vertical energy transfer.

• Dugstad, Johannes Sandang; Fer, Ilker; Lacasce, Joseph Henry; Lama, Marta Sanchez de la & Trodahl, Marta (2019). Lateral Heat Transport in the Lofoten Basin: Near-Surface Pathways and Subsurface Exchange. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 124(5), s. 2992–3006. doi: 10.1029/2018JC014774. Fulltekst i vitenarkiv Vis sammendrag

  The Lofoten Basin in the Nordic Seas plays a central role in the Atlantic overturning circulation by acting as a reservoir for the warm and saline Atlantic Water flow toward the Arctic Ocean. The mass and heat exchange between Atlantic Water and the Lofoten Basin impacts the water mass transformations and the surface heat loss, but the processes governing this exchange are not well understood or quantified. Here we study the circulation in the Nordic Seas and the heat transport in the Lofoten Basin using a combination of Lagrangian and Eulerian methods. We analyze the trajectories of about 150 surface drifters, augmented with a set of about 47,000 surface trajectories calculated using the output from a regional numerical simulation, to investigate the drifter pathways and their exchange with the Lofoten Basin. The drifters reveal that water parcels with long residence time inside the basin contribute substantially to the heat loss and typically enter from south across the outer rim of the Vøring Plateau and, to some extent from east, from the eastern branch of the Norwegian Atlantic Current. The main contributors to the lateral heat transport to the Lofoten Basin are the near‐surface heat transport by the mean flow in the southern sector of the basin and the subsurface eddy fluxes from the Lofoten Escarpment in the east.

• Gjermundsen, Ada; Lacasce, Joseph Henry & Denstad, Liv (2018). The thermally-driven ocean circulation with realistic bathymetry. Journal of Physical Oceanography. ISSN 0022-3670. 48(3), s. 647–665. doi: 10.1175/JPO-D-17-0147.1. Fulltekst i vitenarkiv Vis sammendrag

  The global circulation driven solely by relaxation to an idealized surface temperature profile and to interior mixing is examined. Forcing by winds and evaporation/precipitation is excluded. The resulting circulation resembles the observed in many ways, and the overturning is of similar magnitude. The overturning is driven by large-scale upwelling in the interior (which is relatively large, because of the use of a constant mixing coefficient). The compensating downwelling occurs in the northern North Atlantic and in the Ross and Weddell Seas, with an additional, smaller contribution from the northern North Pacific. The latter is weaker because the Bering Strait limits the northward extent of the flow. The downwelling occurs in frictional layers near the boundaries and depends on the lateral shear in the horizontal flow. The shear, in turn, is linked to the imposed surface temperature gradient via thermal wind, and as such, the downwelling can be reduced or eliminated in selected regions by removing the surface gradient. Doing so in the northern North Atlantic causes the (thermally driven) Antarctic Circumpolar Current to intensify, increasing the sinking along Antarctica. Eliminating the surface gradient in the Southern Ocean increases the sinking in the North Atlantic and Pacific. As there is upwelling also in the western boundary currents, the flow must increase even more to accomplish the necessary downwelling. The implications of the results are then considered, particularly with respect to Arctic intensification of global warming, which will reduce the surface temperature gradient. This research was originally published in the Journal of Physical Oceanography. © 2018 American Meteorological Society

• Gjermundsen, Ada & Lacasce, Joseph Henry (2017). Comparing the linear and nonlinear buoyancy-driven circulation. Tellus A: Dynamic Meteorology and Oceanography. ISSN 0280-6495. 69(1). doi: 10.1080/16000870.2017.1299282. Fulltekst i vitenarkiv Vis sammendrag

  The buoyancy-driven circulation is studied in an idealized domain using two models, one based on the linearized planetary geostrophic equations and a fully nonlinear GCM. The surface buoyancy is specified (relaxed) to a chosen function of latitude in the linear (nonlinear) model. The models yield similar baroclinic flow in the interior, where the surface velocities are primarily zonal, and near the southern boundary, where a westward surface flow feeds the western boundary current (WBC). They differ however in the north. While the linear model has westward surface flow of limited vertical extent near the northern wall, the GCM has baroclinic flow which extends to the bottom with eastward surface velocities. The difference is due to convection, which weakens the stratification in the nonlinear model, amplifying the thermal wind transport associated with the surface buoyancy gradient. The WBC flow in the GCM feeds this, with northward surface flow over its entire length (as seen in nearly all previous similar studies). This in turn determines the meridional overturning circulation, since the WBC accounts for the largest meridional velocities. Roughly half the upwelling occurs in the WBC in the GCM and half in the interior, while the upwelling occurs in the interior and near the southern wall in the linear model. The study highlights the role of convection in modifying the response to the surface buoyancy gradient.

• Lacasce, Joseph Henry (2017). The Prevalence of oceanic surface modes. Geophysical Research Letters. ISSN 0094-8276. 44(21), s. 11,097–11,105. doi: 10.1002/2017GL075430. Fulltekst i vitenarkiv Vis sammendrag

  Satellite observations have revolutionized oceanography, capturing diverse phenomena over much of the globe. However, it remains to understand how surface fields, like sea surface height, reflect the motion occurring at depth. The vertical structure of ocean eddies is often expressed in terms of “baroclinic modes,” which are basis functions derived assuming a flat ocean bottom. Bathymetry alters the modes though, weakening the bottom velocities. Using analytical solutions, we demonstrate that with realistic bathymetry and/or bottom friction, the bottom velocities are nearly zero. The resulting “surface modes” should be ubiquitous in the ocean. This would explain the dominant mode of variability obtained from globally distributed current meter data and is consistent with energy spectra derived from sea surface height data. The results yield a simple way to infer subsurface velocities from satellite data and suggest that ocean analyses should be made in terms of surface modes and topographic waves. This research was originally published in Geophysical Research Letters. © 2017 American Geophysical Union

• Beron-Vera, Francisco J & Lacasce, Joseph Henry (2016). Statistics of simulated and observed pair separations in the Gulf of Mexico. Journal of Physical Oceanography. ISSN 0022-3670. 46(7), s. 2183–2199. doi: 10.1175/JPO-D-15-0127.1. Fulltekst i vitenarkiv
• Balwada, Dhruv; Speer, Kevin G.; Lacasce, Joseph Henry; Owens, W. Brechner; Marshall, John & Ferrari, Raffaele (2016). Circulation and stirring in the Southeast Pacific Ocean and the Scotia sea sectors of the Antarctic Circumpolar Current. Journal of Physical Oceanography. ISSN 0022-3670. 46(7), s. 2005–2027. doi: 10.1175/JPO-D-15-0207.1. Fulltekst i vitenarkiv
• Lama, Marta de La; Lacasce, Joseph Henry & Fuhr, Helle Kristine (2016). The vertical structure of ocean eddies. Dynamics and Statistics of the Climate System. 1(1), s. 1–16. doi: 10.1093/climsys/dzw001. Fulltekst i vitenarkiv
• Balwada, Dhruv; Lacasce, Joseph Henry & Speer, Kevin (2016). Scale-dependent distribution of kinetic energy from surface drifters in the Gulf of Mexico. Geophysical Research Letters. ISSN 0094-8276. 43(20), s. 10,856–10,863. doi: 10.1002/2016GL069405. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2016). Estimating Eulerian energy spectra from drifters. Fluids. 1(4). doi: 10.3390/fluids1040033. Fulltekst i vitenarkiv
• Graff, Lise Seland; Guttu, Sigmund & Lacasce, Joseph Henry (2015). Relative dispersion in the atmosphere from reanalysis winds. Journal of the Atmospheric Sciences. ISSN 0022-4928. 72(7), s. 2769–2785. doi: 10.1175/JAS-D-14-0225.1. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Wang, J. (2015). Estimating subsurface velocities from surface fields with idealized stratification. Journal of Physical Oceanography. ISSN 0022-3670. 45(9), s. 2424–2435. doi: 10.1175/JPO-D-14-0206.1. Fulltekst i vitenarkiv
• Gjermundsen, Ada; Lacasce, Joseph Henry & Graff, Lise Seland (2014). The atmospheric response to surface heating under maximum entropy production. Journal of the Atmospheric Sciences. ISSN 0022-4928. 71(6), s. 2204–2220. doi: 10.1175/JAS-D-13-0181.1. Fulltekst i vitenarkiv Vis sammendrag

  In numerous studies, midlatitude storm tracks have been shown to shift poleward under global warming scenarios. Among the possible causes, changes in sea surface temperature (SST) have been shown to affect both the intensity and the position of the tracks. Increased SSTs can increase both the lateral heating occurring in the tropics and the midlatitude temperature gradients, both of which increase tropospheric baroclinicity. To better understand the response to altered SST, a simplified energy balance model (EBM) is used. This employs the principal of maximum entropy production (MEP) to determine the meridional heat fluxes in the atmosphere. The model is similar to one proposed by Paltridge (1975) but represents only the atmospheric response (the surface temperatures are fixed). The model is then compared with a full atmospheric general circulation model [Community Atmosphere Model, version 3 (CAM3)]. In response to perturbed surface temperatures, EBM exhibits similar changes in (vertically integrated) air temperature, convective heat fluxes, and meridional heat transport. However, the changes in CAM3 are often more localized, particularly at low latitudes. This, in turn, results in a shift of the storm tracks in CAM3, which is largely absent in EBM. EBM is more successful, however, at representing the response to changes in high-latitude heating or cooling. Therefore, MEP is evidently a plausible representation for heat transport in the midlatitudes, but not necessarily at low latitudes. This research was originally published in Journal of the Atmospheric Sciences. © 2014 American Meteorological Society

• Lacasce, Joseph Henry; Ferrari, Raffaele; Marshall, John; Tulloch, Ross; Balwada, D. & Speer, Kevin (2014). Float-derived isopycnal diffusivities in the DIMES experiment. Journal of Physical Oceanography. ISSN 0022-3670. 44(2), s. 764–780. doi: 10.1175/JPO-D-13-0175.1. Fulltekst i vitenarkiv
• Tulloch, Ross; Ferrari, Raffaele; Jahn, Oliver; Klocker, Andreas; Lacasce, Joseph Henry & Ledwell, James R. [Vis alle 10 forfattere av denne artikkelen] (2014). Direct estimate of lateral eddy diffusivity upstream of drake passage. Journal of Physical Oceanography. ISSN 0022-3670. 44(10), s. 2593–2616. doi: 10.1175/JPO-D-13-0120.1. Fulltekst i vitenarkiv
• Graff, Lise Seland & Lacasce, Joseph Henry (2014). Changes in cyclone characteristics in response to modified SSTs. Journal of Climate. ISSN 0894-8755. 27(11), s. 4273–4295. doi: 10.1175/JCLI-D-13-00353.1. Fulltekst i vitenarkiv
• Høydalsvik, Frode; Mauritzen, Cecilie; Orvik, Kjell Arild; Lacasce, Joseph Henry; Lee, Craig M. & Gobat, Jason (2013). Transport estimates of the Western Branch of the Norwegian Atlantic Current from glider surveys. Deep Sea Research Part I: Oceanographic Research Papers. ISSN 0967-0637. 79, s. 86–95. doi: 10.1016/j.dsr.2013.05.005. Fulltekst i vitenarkiv
• Ghaffari, Peygham; Isachsen, Pål Erik & Lacasce, Joseph Henry (2013). Topographic effects on current variability in the Caspian Sea. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 118(12), s. 7107–7116. doi: 10.1002/2013JC009128. Fulltekst i vitenarkiv
• Wang, Jinbo; Flierl, Glenn R.; Lacasce, Joseph Henry; McClean, Julie & Mahadevan, Amala (2013). Reconstructing the Ocean's Interior from Surface Data. Journal of Physical Oceanography. ISSN 0022-3670. 43(8), s. 1611–1626. doi: 10.1175/JPO-D-12-0204.1. Fulltekst i vitenarkiv
• Koszalka, I.; Lacasce, Joseph Henry & Mauritzen, Cecilie (2013). In pursuit of anomalies-Analyzing the poleward transport of Atlantic Water with surface drifters. Deep-Sea Research Part II: Topical Studies in Oceanography. ISSN 0967-0645. 85, s. 96–108. doi: 10.1016/j.dsr2.2012.07.035. Fulltekst i vitenarkiv
• Isachsen, Pål Erik; Koszalka, I. & Lacasce, Joseph Henry (2012). Observed and modeled surface eddy heat fluxes in the eastern Nordic Seas. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 117(C8). doi: 10.1029/2012JC007935. Fulltekst i vitenarkiv
• Koszalka, Inga; Lacasce, Joseph Henry & Mauritzen, Cecilie (2012). In pursuit of anomalies - Analyzing the poleward transport of Atlantic Water with surface drifters. Deep-Sea Research Part II: Topical Studies in Oceanography. ISSN 0967-0645. doi: 10.1016/j.dsr2.2012.07.035. Fulltekst i vitenarkiv
• O'Reilly, Christopher H; Czaja, Arnaud & Lacasce, Joseph Henry (2012). The emergence of zonal ocean jets under large-scale stochastic wind forcing. Geophysical Research Letters. ISSN 0094-8276. 39. doi: 10.1029/2012GL051684. Fulltekst i vitenarkiv
• Isaksen, Ivar S A; Zerefos, C; Wang, W-C; Balis, D.; Eleftheratos, K. & Rognerud, Bjørg [Vis alle 15 forfattere av denne artikkelen] (2012). Attribution of the Arctic ozone column deficit in March 2011. Geophysical Research Letters. ISSN 0094-8276. 39(L24810). doi: 10.1029/2012GL053876. Fulltekst i vitenarkiv Vis sammendrag

  Arctic column ozone reached record low values (∼310 DU) during March of 2011, exposing Arctic ecosystems to enhanced UV-B. We identify the cause of this anomaly using the Oslo CTM2 atmospheric chemistry model driven by ECMWF meteorology to simulate Arctic ozone from 1998 through 2011. CTM2 successfully reproduces the variability in column ozone, from week to week, and from year to year, correctly identifying 2011 as an extreme anomaly over the period. By comparing parallel model simulations, one with all Arctic ozone chemistry turned off on January 1, we find that chemical ozone loss in 2011 is enhanced relative to previous years, but it accounted for only 23% of the anomaly. Weakened transport of ozone from middle latitudes, concurrent with an anomalously strong polar vortex, was the primary cause of the low ozone When the zonal winds relaxed in mid-March 2011, Arctic column ozone quickly recovered.

• Klocker, Andreas; Ferrari, Raffaele & Lacasce, Joseph Henry (2012). Estimating Suppression of Eddy Mixing by Mean Flows. Journal of Physical Oceanography. ISSN 0022-3670. 42(9), s. 1566–1576. doi: 10.1175/JPO-D-11-0205.1. Fulltekst i vitenarkiv
• Melsom, Arne; Counillon, Francois; Lacasce, Joseph Henry & Bertino, Laurent (2012). Forecasting search areas using ensemble ocean circulation modeling. Ocean Dynamics. ISSN 1616-7341. 62(8), s. 1245–1257. doi: 10.1007/s10236-012-0561-5. Fulltekst i vitenarkiv Vis sammendrag

  We investigate trajectory forecasting as an application of ocean circulation ensemble modeling. The ensemble simulations are performed weekly, starting with assimilation of data for various variables from multiple sensors on a range of observational platforms. The ensemble is constructed from 100 members, and member no. 1 is designed as a standard (deterministic) simulation, providing us with a benchmark for the study. We demonstrate the value of the ensemble approach by validating simulated trajectories using data from ocean surface drifting buoys. We find that the ensemble average trajectories are generally closer to the observed trajectories than the corresponding results from a deterministic forecast. We also investigate an alternative model in which velocity perturbations are added to the deterministic results and ensemble mean results, by a first-order stochastic process. The parameters of the stochastic model are tuned to match the dispersion of the ensemble approach. Search areas from the stochastic model give a higher hit ratio of the observations than the results based on the ensemble. However, we find that this is a consequence of a positive skew of the area distribution of the convex hulls of the ensemble trajectory end points.

• Lacasce, Joseph Henry (2012). Surface Quasigeostrophic Solutions and Baroclinic Modes with Exponential Stratification. Journal of Physical Oceanography. ISSN 0022-3670. 42(4), s. 569–580. doi: 10.1175/JPO-D-11-0111.1. Fulltekst i vitenarkiv
• Graff, Lise Seland & Lacasce, Joseph Henry (2012). Changes in the Extratropical Storm Tracks in Response to Changes in SST in an AGCM. Journal of Climate. ISSN 0894-8755. 25(6), s. 1854–1870. doi: 10.1175/JCLI-D-11-00174.1. Fulltekst i vitenarkiv
• Ohlmann, J. Carter; Lacasce, Joseph Henry; Washburn, Libe; Mariano, Arthur J. & Emery, Brian (2012). Relative dispersion observations and trajectory modeling in the Santa Barbara Channel. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 117. doi: 10.1029/2011JC007810. Fulltekst i vitenarkiv
• Andersson, Maria Helena; Orvik, Kjell Arild; Lacasce, Joseph Henry; Koszalka, Inga & Mauritzen, Cecilie (2011). Variability of the Norwegian Atlantic Current and associated eddy field from surface drifters. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 116. doi: 10.1029/2011JC007078. Fulltekst i vitenarkiv
• Mauritzen, Cecilie; Hansen, Edmond; Andersson, Maria Helena; Berx, Barbara; Beszczynska-Möller, Agnieszka & Burud, Ingunn [Vis alle 41 forfattere av denne artikkelen] (2011). Closing the loop - Approaches to monitoring the state of the Arctic Mediterranean during the International Polar Year 2007-2008. Progress in Oceanography. ISSN 0079-6611. 90(1-4), s. 62–89. doi: 10.1016/j.pocean.2011.02.010. Fulltekst i vitenarkiv
• Koszalka, Inga; Lacasce, Joseph Henry; Andersson, Maria Helena; Orvik, Kjell Arild & Mauritzen, Cecilie (2011). Surface circulation in the Nordic Seas from clustered drifters. Deep Sea Research Part I: Oceanographic Research Papers. ISSN 0967-0637. 58(4), s. 468–485. doi: 10.1016/j.dsr.2011.01.007. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Isachsen, Pål Erik (2010). The linear models of the ACC. Progress in Oceanography. ISSN 0079-6611. 84(3-4), s. 139–157. doi: 10.1016/j.pocean.2009.11.002. Fulltekst i vitenarkiv
• Koszalka, Inga & Lacasce, Joseph Henry (2010). Lagrangian analysis by clustering. Ocean Dynamics. ISSN 1616-7341. 60(4), s. 957–972. doi: 10.1007/s10236-010-0306-2. Fulltekst i vitenarkiv
• Griesel, Alexa; Gille, Sarah; Sprintall, Janet; McClean, Julie; Lacasce, Joseph Henry & Maltrud, Matt (2010). Isopycnal diffusivities in the Antarctic Circumpolar Current inferred from Lagrangian floats in an eddying model. Journal of Geophysical Research (JGR): Oceans. ISSN 2169-9275. 115(C06006). doi: 10.1029/2009JC005821. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2010). Relative displacement probability distribution functions from balloons and drifters. Journal of Marine Research. ISSN 0022-2402. 68(3-4), s. 433–457. Fulltekst i vitenarkiv
• Koszalka, Inga; Lacasce, Joseph Henry & Orvik, Kjell Arild (2009). Relative dispersion in the Nordic Seas. Journal of Marine Research. ISSN 0022-2402. 67(4), s. 411–433. doi: 10.1357/002224009790741102. Fulltekst i vitenarkiv
• Koszalka, I.; LaCasce, Joseph H. & Orvik, Kjell Arild (2009). Relative dispersion in the Nordic Seas. Journal of Marine Research. ISSN 0022-2402. 67(4), s. 411–433. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2008). The vortex merger rate in freely decaying, two-dimensional turbulence. Physics of Fluids. ISSN 1070-6631. 20. doi: 10.1063/1.2957020. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2008). Statistics from Lagrangian observations. Progress in Oceanography. ISSN 0079-6611. 77, s. 1–29. doi: 10.1016/j.pocean.2008.02.002. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry; Nøst, O.A. & Isachsen, Pål Erik (2008). The asymmetry of free circulations in closed ocean gyres. Journal of Physical Oceanography. ISSN 0022-3670. 38(2), s. 517–526. doi: 10.1175/2007JPO3789.1. Fulltekst i vitenarkiv
• Isachsen, Pål Erik; Lacasce, Joseph Henry & Pedlosky, Joseph (2007). Rossby wave instability and apparent phase speeds in large ocean basins. Journal of Physical Oceanography. ISSN 0022-3670. 37, s. 1177–1191. doi: 10.1175/JPO3054.1. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Isachsen, Pål Erik (2007). On Sverdrup discontinuities and vortices in the Southwest Indian Ocean. Journal of Physical Oceanography. ISSN 0022-3670. 37, s. 2940–2950. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Mahadevan, A. (2006). Estimating sub-surface horizontal and vertical velocities from sea surface temperature. Journal of Marine Research. ISSN 0022-2402. 64(5), s. 695–721. Fulltekst i vitenarkiv
• Orre, Steinar; Gjevik, Bjørn & LaCasce, Joseph H. (2006). Characterizing chaotic dispersion in a coastal tidal model. Continental Shelf Research. ISSN 0278-4343. 26, s. 1360–1374. doi: 10.1016/j.csr.2005.11.015. Fulltekst i vitenarkiv Vis sammendrag

  Diverse Lagrangian methods are used to study dispersion and mixing in a model in the Norwegian Trondheim fjord. We focus on the tidally driven currents, neglecting wind-forcing, and generate a large number of particle trajectories. We first consider traditional measures (absolute and relative dispersion) involving averages over all particles. We then contour those measures, to gauge the spatial variations. Then we examine a more recently developed measure, the direct Lyapunov exponent (DLE), to further refine the description of the spatial variability. The results suggest regions of strong mixing adjacent to regions with weak mixing, so that particles in nearby regions may experience very distinct evolutions. And M2 dominates the dispersion; adding additional tidal components affects mainly the amplitude of the particle excursions rather than the character of the mixing.

• Lacasce, Joseph Henry (2005). On the Eulerian and Lagrangian velocity distributions in the North Atlantic. Journal of Physical Oceanography. ISSN 0022-3670. 35(12), s. 2327–2336. Fulltekst i vitenarkiv Vis sammendrag

  Velocity probability density functions (PDFs) are calculated using data from subsurface current meters in the western North Atlantic Ocean. The PDFs are weakly, but significantly, non-Gaussian. They deviate from normality because of an excess of energetic events, and there are evidently more such events in the main thermocline than in the deep ocean. The PDFs are also compared with those obtained from subsurface floats in the same region. The PDFs are statistically indistinguishable so long as the float data are averaged in appropriately sized bins. Taking too-small bins yields overly Gaussian float PDFs, and taking too-large bins yields too-non-Gaussian PDFs. With this caveat, the Lagrangian and Eulerian PDFs agree, consistent with expectations from theory and previous numerical simulations.

• Lacasce, Joseph Henry (2005). Statistics of low frequency currents over the western Nordic shelf and slope; part I, current meters. Ocean Dynamics. ISSN 1616-7341. 55(3-4), s. 213–221. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Engedahl, Harald (2005). Statistics of low frequency currents over the western Nordic shelf and slope; part II, model. Ocean Dynamics. ISSN 1616-7341. 55(3-4), s. 222–237. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2004). Diffusivity and viscosity dependence in the linear thermocline. Journal of Marine Research. ISSN 0022-2402. 62, s. 743–769. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Pedlosky, Joseph (2004). The instability of Rossby basin modes and the oceanic eddy field. Journal of Physical Oceanography. ISSN 0022-3670. 34, s. 2027–2041. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Nycander, Jonas (2004). Stable and unstable vortices attached to seamounts. Journal of Fluid Mechanics. ISSN 0022-1120. 507, s. 71–94. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Ohlmann, Carter (2003). Relative dispersion at the surface of the Gulf of Mexico. Journal of Marine Research. ISSN 0022-2402. 61, s. 285–312. Fulltekst i vitenarkiv
• Isachsen, Pål Erik; LaCasce, Joe H; Mauritzen, Cecilie & Hakkinen, Sirpa (2003). Wind-driven variability of the large-scale recirculating flow in the Nordic seas and Arctic Ocean. Journal of Physical Oceanography. ISSN 0022-3670. 33(12), s. 2534–2550. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2003). Wind-forced barotropic flow in sub-polar regions. Journal of Physical Oceanography. ISSN 0022-3670. 33(12), s. 2534–2550. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry & Pedlosky, Joseph (2002). Baroclinic Rossby waves in irregular basins. Journal of Physical Oceanography. ISSN 0022-3670. 32, s. 2828–2847. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2002). On turbulence and normal modes in a basin. Journal of Marine Research. ISSN 0022-2402. 60, s. 431–460. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Lacasce, Joseph Henry; Li, Camille; Gjermundsen, Ada & Kappatou, Christina (2025). Investigating Bjerknes Compensation under the abrupt-x4CO2 CMIP6 experiment. doi: https:/meetingorganizer.copernicus.org/EGU25/EGU25-4868.html. Fulltekst i vitenarkiv Vis sammendrag

  In 1964 J. Bjerknes postulated that, when an anomaly occurs in ocean heat transport (OHT), the atmosphere heat transport (AHT) exhibits an anomaly of opposite sign so that the top of the atmosphere (TOA) transport is approximately preserved. This phenomenon is now known as Bjerknes Compensation (BJC) and has been the object of many studies in the context of steady state climate simulations, on decadal and centennial time scales. Here, we examine BJC under extreme climate forcing, specifically under the quadrupling of atmospheric CO2 in the Coupled Model Intercomparison Project Phase 6 (CMIP6). The models exhibit a pronounced decline in the Atlantic Meridional Overturning Circulation (AMOC), to varying degrees, in response to melting sea ice and increased freshwater runoff. The OHT is reduced accordingly, and this can trigger an increase in AHT, particularly in the Northern Hemisphere. We examine the degree of BJC, in the context of model climate sensitivity. We also examine how changes in overturning in the Southern Hemisphere impact AHT there. The issue is significant, as increased AHT partially compensates for the cooling implied by reduced OHT.

• Smith, Jerome A.; Cessi, Paola; Fer, Ilker; Foltz, Gregory; Fox-Kemper, Baylor & Heywood, Karen [Vis alle 9 forfattere av denne artikkelen] (2020). Data availability principles and practice. Journal of Physical Oceanography. ISSN 0022-3670. 50(12), s. 3377–3378. doi: 10.1175/JPO-D-20-0266.1. Fulltekst i vitenarkiv
• Dugstad, Johannes Sandang; Koszalka, Inga; Isachsen, Pål Erik; Dagestad, Knut-Frode; Fer, Ilker & Lacasce, Joseph Henry (2019). Mass exchange of Atlantic Water with the Lofoten Basin derived from high resolution Lagragian simulations and Eulerian models. Fulltekst i vitenarkiv
• Straume, Eivind Olavson; Gaina, Carmen; Gjermundsen, Ada; Lacasce, Joseph Henry; Klocker, Andreas & Nikurashin, Maxim (2018). Global Miocene paleobathymetry: implications for paleo-ocean circulation. Fulltekst i vitenarkiv
• Dugstad, Johannes Sandang; Lacasce, Joseph Henry; Koszalka, Inga & Fer, Ilker (2017). Observing mass exchange with the Lofoten Basin using surface drifters. Fulltekst i vitenarkiv
• Gjermundsen, Ada; Lacasce, Joseph Henry & Denstad, Liv (2017). On the thermally-driven ocean circulation with realistic topography. Fulltekst i vitenarkiv
• Gaina, Carmen & Lacasce, Joseph Henry (2014). Linking the Tectonic Evolution of the Northeast Atlantic and the Arctic: Paleobathymetry Reconstructions and Paleoceanographic Implications. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2010). The Jet Stream, high and low pressure systems and fronts; Understanding the weather. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2009). Relative dispersion in the Nordic Seas. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2009). Relative dispersion in the Nordic Seas. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2009). Turbulent dispersion in the Nordic Seas. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2009). Relative dispersion in the Nordic Seas. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2009). Relative dispersion in the atmosphere and ocean. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2009). Relative dispersion in the Nordic Seas. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2008). The vortex merger rate in freely-decaying, 2D tubulence. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2008). The vortex merger rate in 2-D turbulence. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2008). The linear models of the ACC. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry (2007). The vortex merger rate in freely-decaying 2-D turbulence. Fulltekst i vitenarkiv
• Førland, Eirik J.; Alfnes, Eli; Amundsen, Helene; Asval, Randi Pytte; Benestad, Rasmus & Debernard, Jens [Vis alle 19 forfattere av denne artikkelen] (2007). Climate change and natural disasters in Norway. An assessment of possible future changes. met.no report 6/2007. Fulltekst i vitenarkiv
• Lacasce, Joseph Henry; Albretsen, Jon & Røed, Lars Petter (2006). Ocean temperatures at Ekofisk. Norwegian Meteorological Institute. Fulltekst i vitenarkiv

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