Barry Ruddick - Profile on Academia.edu (original) (raw)
Papers by Barry Ruddick
Recover of temperature, salinity and potential density from acoustic reflectivity in the ocean
17th Ocean Sciences Meeting, 23-28 February 2014, Honolulu, Hawaii USAWe present the inversion of... more 17th Ocean Sciences Meeting, 23-28 February 2014, Honolulu, Hawaii USAWe present the inversion of temperature, salinity and potential density from time and space-coincident acoustic reflectivity and XBT data in the Gulf of Cadiz, NE Atlantic Ocean. This method recovers low frequency content ( 10 Hz) from acoustic reflectivity. Afterwards, maps of temperature and salinity are calculated from impedance using the GSW equations of state and an empirical T-S relation obtained with Neural Networks. This method allows to recover the main physical oceanographic parameters in the ocean with accuracies of δTsd = 0.1oC, δSsd = 0.09 and δρsd = 0.02kg/m3 for temperature, salinity and potential density respectively, along lateral sections of hundreds of km, covering all the full-depth water column and with vertical and lateral resolutions of 10 m and 100 m, respectively. Acoustic reflectors and inverted potential density are eventually compared to better understanding the contribution of the acoustic reflectivity to the physic observation of the oceanPeer Reviewe
Progress and prospects of seismic oceanography
Deep Sea Research Part I: Oceanographic Research Papers, 2021
Dynamics of Frontal Intrusions and their effects on a Mediterranean Salt Lens. Parameterisation o... more Dynamics of Frontal Intrusions and their effects on a Mediterranean Salt Lens. Parameterisation of the structure, amplitude, and mixing rate of finite-amplitude lateral intrusions. These occur at most oceanic fronts, including the Gulf Stream, and drive crossfrontal mixing. The highly structured quasi-horizontal sound speed perturbations may strongly affect acoustic propagation across such fronts. SPECIFIC OBJECTIVES 1. To understand the role of vertical mixing of salt, heat, mass, and momentum in driving lateral intrusions. 2. To predict the scale, structure, and magnitude of finite-amplitude intrusive features in terms of mesoscale gradients.
Journal of Atmospheric and Oceanic Technology, 2016
Marine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth’... more Marine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth’s subsurface, can also be used in physical oceanography exploration. This method provides vertical and lateral resolutions of O(10–100) m, covering the existing observational gap in oceanic exploration. All MCS data used so far in physical oceanography studies have been acquired using conventional seismic instrumentation originally designed for geological exploration. This work presents the proof of concept of an alternative MCS system that is better adapted to physical oceanography and has two goals: 1) to have an environmentally low-impact acoustic source to minimize any potential disturbance to marine life and 2) to be light and portable, thus being installed on midsize oceanographic vessels. The synthetic experiments simulate the main variables of the source, shooting, and streamer involved in the MCS technique. The proposed system utilizes a 5-s-long exponential chirp source of 208 ...
Deep Sea Research Part A. Oceanographic Research Papers, 1983
Exploration of the California Current System with seismic oceanography
The Mixing of Meddy “Sharon”
Small-Scale Turbulence and Mixing in the Ocean - Proceedings of the 19th International Liege Colloquium on Ocean Hydrodynamics, 1988
... Intl. J. Heat Mass Transfer 14, 57-65. Gregg,, 1980. Three-dimensional mapping of a small the... more ... Intl. J. Heat Mass Transfer 14, 57-65. Gregg,, 1980. Three-dimensional mapping of a small thermohaline intrusion. J. Phys. Oceanogr., 10, 1468-1492. Hart, JE, 1971. On sideways diffusive instability. J. Fluid Mech. 49, 279-288. Page 276. 261 Hebert, D., 1988a. ...
Sounding Out Ocean Fine Structure
Science, 2003
... The Fall 2000 issue of Maritimes had an article by M. Prater and HT Rossby titled “The double... more ... The Fall 2000 issue of Maritimes had an article by M. Prater and HT Rossby titled “The double irony of the Meddy.” D ... Department of Geology and Geophysics, University of Wyoming, offers a presentation about the Summer 2000 cruises on the R/V Maurice Ewing (during which ...
Progress in Oceanography, 2003
This is a review of theories governing growth and evolution of thermohaline intrusive motions. We... more This is a review of theories governing growth and evolution of thermohaline intrusive motions. We discuss theories based on eddy coefficients and salt finger flux ratios, and on molecular Fickian diffusion, drawing relationships and parallels where possible. We discuss linear theories of various physical configurations, effects of rotation and shear, and nonlinear theories. A key requirement for such theories becoming quantitatively correct is the development and field testing of relationships between double-diffusive fluxes and average vertical gradients of temperature and salinity. While we have some ideas about the functional dependencies and rough observational constraints on the magnitudes of such flux/gradient relationships, many questions will not be answered until usable "flux laws" exist. Furthermore, numerical experiments on double-diffusive intrusions are currently feasible, but will have more quantitative meaning when fluxes are parameterised with such laws. We conclude that more work needs to be done in at least two areas. First, tests of linear theory against observations should continue, particularly to discover the extent to which linear theories actually explain the genesis of intrusions. Second, theoretical studies are needed of the nonlinear effects that control the evolution and finite amplitude state of intrusions, since these determine the lateral fluxes of salt, heat, and momentum.
Progress in Oceanography, 2003
Double-diffusion, the mixing of fluids with two constituents of different molecular diffusivities... more Double-diffusion, the mixing of fluids with two constituents of different molecular diffusivities, was originally discovered in the mid-1800's, forgotten, then rediscovered as an "oceanographic curiosity" a century later. Many oceanographers suspect that doublediffusion has major effects on oceanic water masses and circulation, but direct measurement of the effects has proven difficult. In 1996, a Working Group was formed under the auspices of the Scientific Committee on Ocean Research (SCOR WG108), with the goal to: Identify progress and barriers to quantifying oceanic double-diffusive fluxes, and make recommendations for further progress. This document gives a brief history of double-diffusion, a review of evidence of its potential effects in the ocean, and gives an overview of the review articles contained in this volume, written by the Working Group members with the above aim in mind.
Marine Pollution Bulletin, 2011
Observations are presented on dilution and dispersion rates of ballast water discharged under nor... more Observations are presented on dilution and dispersion rates of ballast water discharged under normal operational conditions at the semi-enclosed port of Goderich, Ontario. The ballast water was tagged with Rhodamine-WT dye and microscopic magnetically-attractive tracer particles. Maximum concentrations of dye immediately after discharge were diluted to 1-5% of initial ballast tank concentrations, and within 3 days had decreased to less than 0.1% of initial concentrations. Inside the harbor, there was 10-20% of the ballast water still present after 2 days, consistent with a flushing rate of 0.8-1.15 day À1 . Magnetic particles were collected up to 7.5 km outside the harbor after one day, consistent with a dilution factor of order 10 5 outside the harbor. The results of this study are discussed in the context of ballast water discharge standards proposed by the International Maritime Organization to minimize the introduction of aquatic nonindigenous species through ships' ballast water and sediments.
The Journal of the Acoustical Society of America, 2013
Vertical stability of the fluid particles, mixing, and mesoscale motions in the ocean interior oc... more Vertical stability of the fluid particles, mixing, and mesoscale motions in the ocean interior occur mostly along-isopycnals surfaces. Therefore, potential density profiles with high lateral resolution would provide important information about the fluid dynamic and the general circulation in the ocean. Could we observe density changes from seismic data? Is seismic oceanography able to measure density with enough accuracy? How is the relation between seismic reflectors and isopycnals surfaces? We have inverted oceanic impedance from seismic data and then derived density and potential density surfaces from the oceanic impedance. Results of the inverted potential density have been compared with digitized seismic reflectors to show the relation between isopycnals and reflectors. We have also compare the seismic profiles of the GO Survey with the space-coincident CTDs and space and time-coincident XBTs to understand the nature of the reflectivity and its relation with the physical parame...
Journal of Physical Oceanography, 2007
Thermohaline interleaving is an important mechanism for laterally fluxing salt, heat, and nutrien... more Thermohaline interleaving is an important mechanism for laterally fluxing salt, heat, and nutrients between water masses. Interleaving is driven by a release of potential energy resulting from the differing diffusivities of heat and salt in seawater. The flows are composed of stacked intrusions that flux more and less buoyant water in opposite directions. In this paper, the role of shear instability caused by this juxtaposed motion is investigated. The model described in Walsh and Ruddick is modified to include both the effects of shear-induced turbulence and an improved convective mixing parameterization. Shear and convective mixing play a similar and significant role in interleaving dynamics. In the absence of either instability, cross-front fluxes are increased by approximately 30%. While in situ observations of horizontal diffusivity resulting from interleaving are not yet precise enough to calibrate the parameterizations independently, parameter values based on independent labo...
Journal of Physical Oceanography, 1992
Journal of Physical Oceanography, 1989
Variations in Apparent Mixing Efficiency in the North Atlantic Central Water
Journal of Physical Oceanography, 1997
Microstructure data from the North Atlantic Tracer Release Experiment (NATRE) are presented, prov... more Microstructure data from the North Atlantic Tracer Release Experiment (NATRE) are presented, providing detailed profiles of the thermal variance χ in the upper 360 m of the Canary Basin for the fall and spring seasons. The OsbornCox model is used to compute the ...
Journal of Marine Systems, 2010
Reprocessing of a 326-km long multichannel seismic line acquired in the Tagus Abyssal Plain off W... more Reprocessing of a 326-km long multichannel seismic line acquired in the Tagus Abyssal Plain off W Iberia in 1991 allowed detailed imaging of the thermohaline structure of several mesoscale features within the water column. The interpretation was supported by subsurface float measurements, Sea Level Anomaly (SLA) maps and Sea Surface Temperature (SST) images contemporaneous with the acquisition of the seismic data. Clear images were obtained of the reflective patterns associated with one previously known and one newly discovered meddy, one cyclone, the upper and lower cores of the Mediterranean Undercurrent, and the interface of the high-salinity tongue of the Mediterranean Water with the North Atlantic Central Water. These reveal a complexity and a detail of the lateral variations of the thermohaline structure not easily observed by conventional physical oceanography tools. The mesoscale structures were imaged via reflections from oceanic fine structures of scale 30 m or less. We compare the characteristics of observed reflections with known mechanisms of fine-structure production. Most of the observed reflections are consistent with internal waves and thermohaline intrusions as previously hypothesized. We postulate a new mechanism to explain the formation of the steeply sloping reflections that outline the meddy and other features, involving frontogenetic isopycnal advection, formation of thermohaline intrusions, and tilting of the intrusive layers by mesoscale shear flows. The imaging technique therefore shows the relationship between mesoscale features and the fine-scale oceanographic phenomena associated with mixing, including steeply-sloped structures that would otherwise not be tracked using CTD profiles alone.
Journal of Marine Research, 2010
We develop and test a method to observationally estimate lateral intrusive heat flux across a fro... more We develop and test a method to observationally estimate lateral intrusive heat flux across a front. The model combines that of , in which lateral cross-frontal advection by intrusions creates vertical temperature gradients, and Osborn and Cox (1972) in which vertical mixing of those gradients creates thermal microstructure that is dissipated by molecular conduction of heat. Observations of thermal microstructure dissipation T are then used to estimate the production by intrusions, and hence the lateral heat flux and diffusivity. This method does not depend on the precise mechanism(s) of mixing, or on the dynamical mechanisms driving the frontal intrusions. It relies on several assumptions: (1) lateral cross-frontal advection produces diapycnal temperature gradients that are mixed locally, (2) thermal variance is dissipated locally and not exported, (3) intrusion scales are larger than turbulence scales, and (4) isotropy of temperature microstructure is assumed in order to estimate T . The method is tested using microstructure observations in Meddy "Sharon," where the erosion rate and associated lateral heat flux are known from successive mesoscale hydrographic observations ). An expression is developed for the production (lateral heat flux times lateral temperature gradient, expected to equal T ) in a front of steady shape that is eroding (detraining) at a steady rate; the production is proportional to the erosion speed and the square of the cross-frontal temperature contrast, both of which are well-known from observations. The qualitative structure and integrated value of the dissipation agree well with model assumptions and predictions: thermal variance produced by lateral intrusive heat flux is dissipated locally, dissipation in intrusive regions dominates total dissipation, and the total dissipation agrees with the observed erosion rate, all of which suggests that microstructure observations can be used to estimate intrusive heat flux. A direct comparison was made between lateral heat flux estimated from mesoscale Meddy structure plus the known rate of erosion, and lateral flux based on microscale temperature dissipation, with excellent agreement in the frontal zone and poorer agreement where lateral temperature gradient is too small to accurately measure.
Journal of Geophysical Research: Oceans, 1990
The behavior of an anticyclonic coherent eddy in a barotropic strain field is examined using a sh... more The behavior of an anticyclonic coherent eddy in a barotropic strain field is examined using a shallow water equation model. The “lens equation” model, a set of eight nonlinear ordinary differential equations, was first exploited by Cushman‐Roisin et al. [1985] and Ripa [1987] to examine the behavior and stability of isolated vortices. In this paper we expand the application to include the effect of external fields on the vortex, in particular, an external barotropic strain field. The equilibrium solutions to the equations are found to be elliptical lenses aligned along the high‐pressure axis of the strain field (up to a rate of strain of 0.1f), and an aphysical rain gutter aligned along the strain field outflow axes. The linear stability of the elliptical solutions is explored, and it is found that regardless of the rate of strain, vortices with ellipticities (E) greater than ∼2 are unstable to lens‐like and higher order perturbations, and that this value of E corresponds to a maxi...
Recover of temperature, salinity and potential density from acoustic reflectivity in the ocean
17th Ocean Sciences Meeting, 23-28 February 2014, Honolulu, Hawaii USAWe present the inversion of... more 17th Ocean Sciences Meeting, 23-28 February 2014, Honolulu, Hawaii USAWe present the inversion of temperature, salinity and potential density from time and space-coincident acoustic reflectivity and XBT data in the Gulf of Cadiz, NE Atlantic Ocean. This method recovers low frequency content ( 10 Hz) from acoustic reflectivity. Afterwards, maps of temperature and salinity are calculated from impedance using the GSW equations of state and an empirical T-S relation obtained with Neural Networks. This method allows to recover the main physical oceanographic parameters in the ocean with accuracies of δTsd = 0.1oC, δSsd = 0.09 and δρsd = 0.02kg/m3 for temperature, salinity and potential density respectively, along lateral sections of hundreds of km, covering all the full-depth water column and with vertical and lateral resolutions of 10 m and 100 m, respectively. Acoustic reflectors and inverted potential density are eventually compared to better understanding the contribution of the acoustic reflectivity to the physic observation of the oceanPeer Reviewe
Progress and prospects of seismic oceanography
Deep Sea Research Part I: Oceanographic Research Papers, 2021
Dynamics of Frontal Intrusions and their effects on a Mediterranean Salt Lens. Parameterisation o... more Dynamics of Frontal Intrusions and their effects on a Mediterranean Salt Lens. Parameterisation of the structure, amplitude, and mixing rate of finite-amplitude lateral intrusions. These occur at most oceanic fronts, including the Gulf Stream, and drive crossfrontal mixing. The highly structured quasi-horizontal sound speed perturbations may strongly affect acoustic propagation across such fronts. SPECIFIC OBJECTIVES 1. To understand the role of vertical mixing of salt, heat, mass, and momentum in driving lateral intrusions. 2. To predict the scale, structure, and magnitude of finite-amplitude intrusive features in terms of mesoscale gradients.
Journal of Atmospheric and Oceanic Technology, 2016
Marine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth’... more Marine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth’s subsurface, can also be used in physical oceanography exploration. This method provides vertical and lateral resolutions of O(10–100) m, covering the existing observational gap in oceanic exploration. All MCS data used so far in physical oceanography studies have been acquired using conventional seismic instrumentation originally designed for geological exploration. This work presents the proof of concept of an alternative MCS system that is better adapted to physical oceanography and has two goals: 1) to have an environmentally low-impact acoustic source to minimize any potential disturbance to marine life and 2) to be light and portable, thus being installed on midsize oceanographic vessels. The synthetic experiments simulate the main variables of the source, shooting, and streamer involved in the MCS technique. The proposed system utilizes a 5-s-long exponential chirp source of 208 ...
Deep Sea Research Part A. Oceanographic Research Papers, 1983
Exploration of the California Current System with seismic oceanography
The Mixing of Meddy “Sharon”
Small-Scale Turbulence and Mixing in the Ocean - Proceedings of the 19th International Liege Colloquium on Ocean Hydrodynamics, 1988
... Intl. J. Heat Mass Transfer 14, 57-65. Gregg,, 1980. Three-dimensional mapping of a small the... more ... Intl. J. Heat Mass Transfer 14, 57-65. Gregg,, 1980. Three-dimensional mapping of a small thermohaline intrusion. J. Phys. Oceanogr., 10, 1468-1492. Hart, JE, 1971. On sideways diffusive instability. J. Fluid Mech. 49, 279-288. Page 276. 261 Hebert, D., 1988a. ...
Sounding Out Ocean Fine Structure
Science, 2003
... The Fall 2000 issue of Maritimes had an article by M. Prater and HT Rossby titled “The double... more ... The Fall 2000 issue of Maritimes had an article by M. Prater and HT Rossby titled “The double irony of the Meddy.” D ... Department of Geology and Geophysics, University of Wyoming, offers a presentation about the Summer 2000 cruises on the R/V Maurice Ewing (during which ...
Progress in Oceanography, 2003
This is a review of theories governing growth and evolution of thermohaline intrusive motions. We... more This is a review of theories governing growth and evolution of thermohaline intrusive motions. We discuss theories based on eddy coefficients and salt finger flux ratios, and on molecular Fickian diffusion, drawing relationships and parallels where possible. We discuss linear theories of various physical configurations, effects of rotation and shear, and nonlinear theories. A key requirement for such theories becoming quantitatively correct is the development and field testing of relationships between double-diffusive fluxes and average vertical gradients of temperature and salinity. While we have some ideas about the functional dependencies and rough observational constraints on the magnitudes of such flux/gradient relationships, many questions will not be answered until usable "flux laws" exist. Furthermore, numerical experiments on double-diffusive intrusions are currently feasible, but will have more quantitative meaning when fluxes are parameterised with such laws. We conclude that more work needs to be done in at least two areas. First, tests of linear theory against observations should continue, particularly to discover the extent to which linear theories actually explain the genesis of intrusions. Second, theoretical studies are needed of the nonlinear effects that control the evolution and finite amplitude state of intrusions, since these determine the lateral fluxes of salt, heat, and momentum.
Progress in Oceanography, 2003
Double-diffusion, the mixing of fluids with two constituents of different molecular diffusivities... more Double-diffusion, the mixing of fluids with two constituents of different molecular diffusivities, was originally discovered in the mid-1800's, forgotten, then rediscovered as an "oceanographic curiosity" a century later. Many oceanographers suspect that doublediffusion has major effects on oceanic water masses and circulation, but direct measurement of the effects has proven difficult. In 1996, a Working Group was formed under the auspices of the Scientific Committee on Ocean Research (SCOR WG108), with the goal to: Identify progress and barriers to quantifying oceanic double-diffusive fluxes, and make recommendations for further progress. This document gives a brief history of double-diffusion, a review of evidence of its potential effects in the ocean, and gives an overview of the review articles contained in this volume, written by the Working Group members with the above aim in mind.
Marine Pollution Bulletin, 2011
Observations are presented on dilution and dispersion rates of ballast water discharged under nor... more Observations are presented on dilution and dispersion rates of ballast water discharged under normal operational conditions at the semi-enclosed port of Goderich, Ontario. The ballast water was tagged with Rhodamine-WT dye and microscopic magnetically-attractive tracer particles. Maximum concentrations of dye immediately after discharge were diluted to 1-5% of initial ballast tank concentrations, and within 3 days had decreased to less than 0.1% of initial concentrations. Inside the harbor, there was 10-20% of the ballast water still present after 2 days, consistent with a flushing rate of 0.8-1.15 day À1 . Magnetic particles were collected up to 7.5 km outside the harbor after one day, consistent with a dilution factor of order 10 5 outside the harbor. The results of this study are discussed in the context of ballast water discharge standards proposed by the International Maritime Organization to minimize the introduction of aquatic nonindigenous species through ships' ballast water and sediments.
The Journal of the Acoustical Society of America, 2013
Vertical stability of the fluid particles, mixing, and mesoscale motions in the ocean interior oc... more Vertical stability of the fluid particles, mixing, and mesoscale motions in the ocean interior occur mostly along-isopycnals surfaces. Therefore, potential density profiles with high lateral resolution would provide important information about the fluid dynamic and the general circulation in the ocean. Could we observe density changes from seismic data? Is seismic oceanography able to measure density with enough accuracy? How is the relation between seismic reflectors and isopycnals surfaces? We have inverted oceanic impedance from seismic data and then derived density and potential density surfaces from the oceanic impedance. Results of the inverted potential density have been compared with digitized seismic reflectors to show the relation between isopycnals and reflectors. We have also compare the seismic profiles of the GO Survey with the space-coincident CTDs and space and time-coincident XBTs to understand the nature of the reflectivity and its relation with the physical parame...
Journal of Physical Oceanography, 2007
Thermohaline interleaving is an important mechanism for laterally fluxing salt, heat, and nutrien... more Thermohaline interleaving is an important mechanism for laterally fluxing salt, heat, and nutrients between water masses. Interleaving is driven by a release of potential energy resulting from the differing diffusivities of heat and salt in seawater. The flows are composed of stacked intrusions that flux more and less buoyant water in opposite directions. In this paper, the role of shear instability caused by this juxtaposed motion is investigated. The model described in Walsh and Ruddick is modified to include both the effects of shear-induced turbulence and an improved convective mixing parameterization. Shear and convective mixing play a similar and significant role in interleaving dynamics. In the absence of either instability, cross-front fluxes are increased by approximately 30%. While in situ observations of horizontal diffusivity resulting from interleaving are not yet precise enough to calibrate the parameterizations independently, parameter values based on independent labo...
Journal of Physical Oceanography, 1992
Journal of Physical Oceanography, 1989
Variations in Apparent Mixing Efficiency in the North Atlantic Central Water
Journal of Physical Oceanography, 1997
Microstructure data from the North Atlantic Tracer Release Experiment (NATRE) are presented, prov... more Microstructure data from the North Atlantic Tracer Release Experiment (NATRE) are presented, providing detailed profiles of the thermal variance χ in the upper 360 m of the Canary Basin for the fall and spring seasons. The OsbornCox model is used to compute the ...
Journal of Marine Systems, 2010
Reprocessing of a 326-km long multichannel seismic line acquired in the Tagus Abyssal Plain off W... more Reprocessing of a 326-km long multichannel seismic line acquired in the Tagus Abyssal Plain off W Iberia in 1991 allowed detailed imaging of the thermohaline structure of several mesoscale features within the water column. The interpretation was supported by subsurface float measurements, Sea Level Anomaly (SLA) maps and Sea Surface Temperature (SST) images contemporaneous with the acquisition of the seismic data. Clear images were obtained of the reflective patterns associated with one previously known and one newly discovered meddy, one cyclone, the upper and lower cores of the Mediterranean Undercurrent, and the interface of the high-salinity tongue of the Mediterranean Water with the North Atlantic Central Water. These reveal a complexity and a detail of the lateral variations of the thermohaline structure not easily observed by conventional physical oceanography tools. The mesoscale structures were imaged via reflections from oceanic fine structures of scale 30 m or less. We compare the characteristics of observed reflections with known mechanisms of fine-structure production. Most of the observed reflections are consistent with internal waves and thermohaline intrusions as previously hypothesized. We postulate a new mechanism to explain the formation of the steeply sloping reflections that outline the meddy and other features, involving frontogenetic isopycnal advection, formation of thermohaline intrusions, and tilting of the intrusive layers by mesoscale shear flows. The imaging technique therefore shows the relationship between mesoscale features and the fine-scale oceanographic phenomena associated with mixing, including steeply-sloped structures that would otherwise not be tracked using CTD profiles alone.
Journal of Marine Research, 2010
We develop and test a method to observationally estimate lateral intrusive heat flux across a fro... more We develop and test a method to observationally estimate lateral intrusive heat flux across a front. The model combines that of , in which lateral cross-frontal advection by intrusions creates vertical temperature gradients, and Osborn and Cox (1972) in which vertical mixing of those gradients creates thermal microstructure that is dissipated by molecular conduction of heat. Observations of thermal microstructure dissipation T are then used to estimate the production by intrusions, and hence the lateral heat flux and diffusivity. This method does not depend on the precise mechanism(s) of mixing, or on the dynamical mechanisms driving the frontal intrusions. It relies on several assumptions: (1) lateral cross-frontal advection produces diapycnal temperature gradients that are mixed locally, (2) thermal variance is dissipated locally and not exported, (3) intrusion scales are larger than turbulence scales, and (4) isotropy of temperature microstructure is assumed in order to estimate T . The method is tested using microstructure observations in Meddy "Sharon," where the erosion rate and associated lateral heat flux are known from successive mesoscale hydrographic observations ). An expression is developed for the production (lateral heat flux times lateral temperature gradient, expected to equal T ) in a front of steady shape that is eroding (detraining) at a steady rate; the production is proportional to the erosion speed and the square of the cross-frontal temperature contrast, both of which are well-known from observations. The qualitative structure and integrated value of the dissipation agree well with model assumptions and predictions: thermal variance produced by lateral intrusive heat flux is dissipated locally, dissipation in intrusive regions dominates total dissipation, and the total dissipation agrees with the observed erosion rate, all of which suggests that microstructure observations can be used to estimate intrusive heat flux. A direct comparison was made between lateral heat flux estimated from mesoscale Meddy structure plus the known rate of erosion, and lateral flux based on microscale temperature dissipation, with excellent agreement in the frontal zone and poorer agreement where lateral temperature gradient is too small to accurately measure.
Journal of Geophysical Research: Oceans, 1990
The behavior of an anticyclonic coherent eddy in a barotropic strain field is examined using a sh... more The behavior of an anticyclonic coherent eddy in a barotropic strain field is examined using a shallow water equation model. The “lens equation” model, a set of eight nonlinear ordinary differential equations, was first exploited by Cushman‐Roisin et al. [1985] and Ripa [1987] to examine the behavior and stability of isolated vortices. In this paper we expand the application to include the effect of external fields on the vortex, in particular, an external barotropic strain field. The equilibrium solutions to the equations are found to be elliptical lenses aligned along the high‐pressure axis of the strain field (up to a rate of strain of 0.1f), and an aphysical rain gutter aligned along the strain field outflow axes. The linear stability of the elliptical solutions is explored, and it is found that regardless of the rate of strain, vortices with ellipticities (E) greater than ∼2 are unstable to lens‐like and higher order perturbations, and that this value of E corresponds to a maxi...