ORCID Profile
0000-0002-4430-0668
Current Organisations
CHU-Sainte Justine Research Center
,
Pacific Region Institute of Ocean Sciences
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Geophysics | Physical Oceanography | Geophysical Fluid Dynamics
Expanding Knowledge in the Earth Sciences | Physical and Chemical Conditions of Water in Marine Environments | Climate Change Models |
Publisher: American Meteorological Society
Date: 04-2016
DOI: 10.1175/JTECH-D-15-0218.1
Abstract: A technique is presented to derive the dissipation of turbulent kinetic energy ϵ by using the maximum likelihood estimator (MLE) to fit a theoretical or known empirical model to turbulence shear spectral observations. The commonly used integration method relies on integrating the shear spectra in the viscous range, thus requiring the resolution of the highest wavenumbers of the turbulence shear spectrum. With current technology, the viscous range is not resolved at sufficiently large wavenumbers to estimate high ϵ however, long inertial subranges can be resolved, making spectral fitting over both this subrange and the resolved portion of the viscous range an attractive method for deriving ϵ . The MLE takes into account the chi-distributed properties of the spectral observations, and so it does not rely on the log-transformed spectral observations. This fitting technique can thus take advantage of both the inertial and viscous subranges, a portion of both, or simply one of the subranges. This flexibility allows a broad range of ϵ to be resolved. The estimated ϵ is insensitive to the range of wavenumbers fitted with the model, provided the noise-dominated portion of the spectra and the low wavenumbers impacted by the mean flow are avoided. For W kg −1 , the MLE fitting estimates agree with those obtained by integrating the spectral observations. However, with increasing ϵ the viscous subrange is not fully resolved and the integration method progressively starts to underestimate ϵ compared with the values obtained from fitting the spectral observations.
Publisher: Wiley
Date: 07-2011
Publisher: Wiley
Date: 14-08-2019
DOI: 10.1002/LNO.11295
Publisher: Wiley
Date: 26-10-2018
DOI: 10.1002/LNO.11051
Publisher: American Geophysical Union (AGU)
Date: 11-2011
DOI: 10.1029/2011JC007214
Abstract: The near seabed mean and turbulent processes on the continental slope were measured for a three week period using an array of acoustic‐Doppler velocimeters and thermistors over the bottom 30 m at the 400 m isobath. Baroclinic motions with characteristics similar to internal bores or boluses propagated onshore during the flood phase of both spring and neap tides. The arrival time of these internal bores at our measurement site varied amongst tidal cycles and their characteristics were not highly correlated with the litude of the barotropic tidal forcing. The passage of the internal bores was associated with large turbulent overturns, enhanced turbulent kinetic energy dissipation (ε 10 −6 W kg −1 ) and intensified currents ( times the barotropic forcing) within meters of the seabed. During the deployment, stratification and shear competed to govern our observed overturning length scale (≲4 m) that were characterized by the Ellison length scale L E . Only measurements closest to the seabed (1.7 m) were described by the log law‐of‐the‐wall generally both buoyancy and the presence of the bottom boundary influenced L E , while sometimes flow‐induced shear determined L E . As the distance of our measurements from the seabed increased, the influence of buoyancy became more pronounced. These results highlight that a more general descriptor of the overturning length scale is necessary for complex stratified shear flows.
Publisher: Copernicus GmbH
Date: 28-10-2021
Abstract: Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tides interacting with the topography at the head of the Laurentian Channel. During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature as well as near-surface water s les collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to s le in tandem with its ice-breaking and ship escorting operations. This opportunistic s ling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and the Gulf of St. Lawrence. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the head. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.
Publisher: American Meteorological Society
Date: 10-2017
DOI: 10.1175/JTECH-D-16-0250.1
Abstract: Ocean mixing has historically been estimated using Osborn’s model by measuring the rate of dissipation of turbulent kinetic energy ϵ and the background density stratification N while assuming a value of the flux Richardson number . A constant is typically assumed, despite mounting field, laboratory, and modeling evidence that varies. This challenge can be overcome by estimating the turbulent diffusivity of heat using the Osborn–Cox model. This model, however, requires measuring the rate of dissipation of thermal variance χ , which has historically been challenging, particularly in energetic flows because the high wavenumbers of the temperature gradient spectra are unresolved with current technology. To overcome this difficulty, a method is described that determines χ by spectral fitting to the inertial-convective (IC) subrange of the temperature gradient spectra. While this concept has been exploited for moored time series, particularly near the bottom boundary, it has yet to be adapted to vertical microstructure profilers such as gliders, and autonomous and ship-based vertical profilers from which there are the most measurements. By using the IC subrange, χ , and hence , can be estimated even in very energetic events—precisely the conditions requiring more field observations. During less energetic periods, the temperature gradient spectra can also be integrated to obtain χ . By combining these two techniques, microstrucure profiles at a field site known for its very energetic internal waves are analyzed. This study demonstrates that the spectral fitting approach resolves intense mixing events with . By equating the Osborn and Osborn–Cox models, indirect estimates for can also be obtained.
Publisher: American Meteorological Society
Date: 11-2016
DOI: 10.1175/JTECH-D-16-0041.1
Abstract: For measurements from either profiling or moored instruments, several processing techniques exist to estimate the dissipation rate of turbulent kinetic energy ϵ , a core quantity used to determine oceanic mixing rates. Moored velocimeters can provide long-term measurements of ϵ , but they can be plagued by motion-induced contamination. To remove this contamination, two methodologies are presented that use independent measurements of the instrument’s acceleration and rotation in space. The first is derived from the relationship between the spectra (cospectra) and the variance (covariance) of a time series. The cospectral technique recovers the environmental (or true) velocity spectrum by summing the measured spectrum, the motion-induced spectrum, and the cospectrum between the motion-induced and measured velocities. The second technique recovers the environmental spectrum by correcting the measured spectrum with the squared coherency, essentially assuming that the measured signal shares variance with either the environmental signal or the motion signal. Both techniques are applied to moored velocimeters at 7.5 and 20.5 m above the seabed in 105 m of water. By estimating the orbital velocities from their respective spectra and comparing them against those obtained from nearby wave measurements, the study shows that the surface wave signature is recovered with the cospectral technique, while it is underpredicted with the squared coherency technique. The latter technique is particularly problematic when the instrument’s motion is in phase with the orbital (environmental) velocities, as it removes variance that should have been added to the measured spectrum. The estimated ϵ from the cospectral technique compares well with estimates from nearby microstructure velocity shear vertical profiles.
Publisher: American Geophysical Union (AGU)
Date: 09-02-2021
DOI: 10.1029/2020GL089455
Abstract: Using field, numerical, and laboratory studies, we consider the roles of both shear and convection in driving mixing in the interior of the density‐stratified ocean. Shear mixing dominates when the Richardson number Ri 0.25, convective mixing dominates when Ri 1.0, and in the intermediate regime when 0.25 Ri 1.0 both shear and convection can contribute to mixing. For pure shear mixing the mixing efficiency Ri f approaches 0.5, while for pure convective mixing the mixing efficiency Ri f approaches 0.75. The diapycnal diffusivities for the two mechanisms are given by very different expressions. Despite these complexities, a simple mixing length model using the mean flow shear S provides robust estimates of diffusivity across the range 0 Ri 2. To account for the roles of both shear and convection over this range of Ri , we also formulate a modified version of the empirical KPP model for parameterizing ocean mixing in numerical models.
Publisher: American Geophysical Union (AGU)
Date: 09-2013
DOI: 10.1002/JGRC.20292
Publisher: Springer Science and Business Media LLC
Date: 12-01-2017
Publisher: Copernicus GmbH
Date: 07-07-2021
DOI: 10.5194/OS-2021-59
Abstract: Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the Estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tidal-upwelling at the Head of the Laurentian Channel (HLC). During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature and near-surface water s les collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to s le in tandem with its icebreaking and ship escorting operations. This opportunistic s ling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and Gulf. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the Gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the HLC. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the Estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.
Publisher: Springer Science and Business Media LLC
Date: 15-02-2019
DOI: 10.1038/S41467-019-08800-2
Abstract: The original version of this Article contained an error in the spelling of the author Laurence Faivre, which was incorrectly given as Laurence Faive. This has now been corrected in both the PDF and HTML versions of the Article.
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-2023
Publisher: Wiley
Date: 15-03-2021
Publisher: Elsevier BV
Date: 03-2019
Publisher: American Geophysical Union (AGU)
Date: 23-03-2018
DOI: 10.1002/2017GL076789
Publisher: American Geophysical Union (AGU)
Date: 2018
DOI: 10.1002/2017JC013242
Location: Canada
Start Date: 2021
End Date: 2006
Funder: Royal Society of New Zealand
View Funded ActivityStart Date: 2005
End Date: 2006
Funder: Natural Sciences and Engineering Research Council
View Funded ActivityStart Date: 2004
End Date: 2005
Funder: Natural Sciences and Engineering Research Council
View Funded ActivityStart Date: 2018
End Date: 2020
Funder: Australian Research Council
View Funded ActivityStart Date: 2017
End Date: 2018
Funder: Natural Sciences and Engineering Research Council
View Funded ActivityStart Date: 2018
End Date: 12-2022
Amount: $387,152.00
Funder: Australian Research Council
View Funded Activity