James Girton - Academia.edu (original) (raw)
Papers by James Girton
Deep-Sea Research Part I-Oceanographic Research Papers, 2014
The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper con... more The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean's role in climate.
This study examines water property distributions in the deep layer of the South China Sea using a... more This study examines water property distributions in the deep layer of the South China Sea using all available hydrographic data. Our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the Pacific into the South China Sea through the Luzon Strait. Applying hydraulic theory with assumptions of zero potential vorticity and flat
The overflow of dense water from the Nordic Seas through the Faroe Bank Channel (FBC) has attribu... more The overflow of dense water from the Nordic Seas through the Faroe Bank Channel (FBC) has attributes suggesting hydraulic control, including an asymmetry across the sill reminiscent of flow over a dam. However, because of the influence of the earth's rotation, as well as the presence of continuous gradients in velocity and density, the standard approach of looking for a
Journal of Geophysical Research, 2003
We report on a combined modeling and observational effort to understand the Denmark Strait Overfl... more We report on a combined modeling and observational effort to understand the Denmark Strait Overflow (DSO). Four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution. The observations reveal the mean path of the dense water, as well as the presence of strong barotropic flows, energetic variability, and strong bottom friction and
Two recent surveys of velocity, temperature and salinity in the Denmark Strait are used to charac... more Two recent surveys of velocity, temperature and salinity in the Denmark Strait are used to characterize the flo w structure, transport and dynamics of the dense overflo w from the Nordic Seas. The mean transport of dense water found at the sill is indistinguishable from measurements made in 1973 (to within 20%), and the statistics of variability are similarly identical.
Working Conference on Current Measurement, 2005
We developed an autonomous ocean profiling velocity and density float that provides exceptional v... more We developed an autonomous ocean profiling velocity and density float that provides exceptional vertical coverage and temporal resolution to depths of 2000 m for deployments of many years. Electrodes were added to the exterior of standard WRC APEX floats, and electronics were added inside. The electrode voltages result from the motion of seawater and the instrument through the Earth's magnetic
Journal of Physical Oceanography
An integrated analysis of turbulence observations from four unique instrument platforms obtained ... more An integrated analysis of turbulence observations from four unique instrument platforms obtained over the Hawaiian Ridge leads to an assessment of the vertical, cross-ridge, and along-ridge structure of turbulence dissipation rate and diffusivity. The diffusivity near the seafloor was, on average, 15 times that in the midwater column. At 1000-m depth, the diffusivity atop the ridge was 30 times that 10 km off the ridge, decreasing to background oceanic values by 60 km. A weak (factor of 2) spring-neap variation in dissipation was observed. The observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide (E ) and the depth-integrated dissipation (D), such that D ϳ E 1Ϯ0.5 at sites along the ridge. This kinematic relationship is supported by combining a simple knife-edge model to estimate internal tide generation, with wave-wave interaction time scales to estimate dissipation. The along-ridge kinematic relationship and the observed vertical and cross-ridge structures are used to extrapolate the relatively sparse observations along the length of the ridge, giving an estimate of 3 Ϯ 1.5 GW of tidal energy lost to turbulence dissipation within 60 km of the ridge. This is roughly 15% of the energy estimated to be lost from the barotropic tide.
Journal of Physical Oceanography, 2015
Deep-Sea Research Part I-Oceanographic Research Papers, 2014
The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper con... more The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean's role in climate.
In ONR's CBLAST Hurricane research program observations were made of the upper ocean's re... more In ONR's CBLAST Hurricane research program observations were made of the upper ocean's response to Hurricane Frances. Three EM-APEX floats (velocity sensing versions of Webb Research APEX floats) and two Lagrangian floats were deployed north of Hispaniola from a C-130 aircraft ahead of Hurricane Frances in September 2004. The EM-APEX floats measured T, S and V over the upper 500
Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society, 2010
Turbulent diapycnal mixing in the ocean controls the transport of heat, freshwater, dissolved gas... more Turbulent diapycnal mixing in the ocean controls the transport of heat, freshwater, dissolved gases, nutrients, and pollutants. Though many present generation climate models represent turbulent mixing with a simplistic diffusivity below the surface mixed layer, the last two decades of ocean mixing research have instead revealed dramatic spatial and temporal heterogeneity in ocean mixing. Climate models that do not appropriately represent the turbulent fluxes of heat, momentum, and CO2 across critical interfaces will not accurately represent the ocean's role in present or future climate. An accurate picture of the worldwide geography of mixing requires a vastly increased database of observations. Unfortunately, traditional microstructure estimates of turbulent mixing are expensive, difficult, and rare. A key development of the last decade has been the development of tools to estimate the turbulent mixing rate from finescale (order 10-50 meter resolution) measurements of internal-wave shear and vertical strain. Global arrays such as the Argo program provide an unprecedented and as yet underdeveloped opportunity to define the global internal wave climate, and in turn identify mixing patterns and hotspots.
Journal of Physical Oceanography, 2006
... Girton, James B., Lawrence J. Pratt, David A. Sutherland, James F. Price, 2006: Is the Faroe ... more ... Girton, James B., Lawrence J. Pratt, David A. Sutherland, James F. Price, 2006: Is the Faroe Bank Channel Overflow Hydraulically Controlled?. J. Phys. Oceanogr., 36, 23402349. ... Is the Faroe Bank Channel Overflow Hydraulically Controlled? James B. Girton ...
Oceanography, 2011
... Authors. James B. Girton Applied Physics Laboratory, University of Washington, Seattle, WA, U... more ... Authors. James B. Girton Applied Physics Laboratory, University of Washington, Seattle, WA, USA. ... Geophysical Research Letters 34, L24601. [CrossRef]. Arango, HG, JC Levin, EN Curchitser, B. Zhang, AM Moore, W. Han, AL Gordon, CM Lee, and JB Girton. 2011. ...
Ocean Modelling, 2006
A series of idealised numerical simulations of dense water flowing down a broad uniform slope are... more A series of idealised numerical simulations of dense water flowing down a broad uniform slope are presented, employing both a z-coordinate model (the MIT general circulation model) and an isopycnal coordinate model (the Hallberg Isopycnal Model). Calculations are carried out at several different horizontal and vertical resolutions, and for a range of physical parameters. A subset of calculations are carried out at very high resolution using the non-hydrostatic variant of the MITgcm. In all calculations dense water descends the slope while entraining and mixing with ambient fluid. The dependence of entrainment, mixing and down-slope descent on resolution and vertical coordinate are assessed. At very coarse resolutions the z-coordinate model generates excessive spurious mixing, and dense water has difficulty descending the slope. However, at intermediate resolutions the mixing in the z-coordinate model is less than found in the high-resolution non-hydrostatic simulations, and dense water descends further down the slope. Iso-1463-5003/$ -see front matter Ó
Journal of Physical Oceanography, 2011
... JB Girton ... Invaluable assistance with the work was provided by Ryan Abernathy, Larry Ander... more ... JB Girton ... Invaluable assistance with the work was provided by Ryan Abernathy, Larry Anderson, Angel Ruiz Angulo, Magdalena Carranza, David Ciochetto, Gillian Damerell, Ken Decoteau, Catherine Grendi, Brian Guest, Jay Hooper, Leah Houghton, Byron Kilbourne, Valery ...
Journal of Physical Oceanography, 2006
An integrated analysis of turbulence observations from four unique instrument platforms obtained ... more An integrated analysis of turbulence observations from four unique instrument platforms obtained over the Hawaiian Ridge leads to an assessment of the vertical, cross-ridge, and along-ridge structure of turbulence dissipation rate and diffusivity. The diffusivity near the seafloor was, on average, 15 times that in the midwater column. At 1000-m depth, the diffusivity atop the ridge was 30 times that 10 km off the ridge, decreasing to background oceanic values by 60 km. A weak (factor of 2) spring-neap variation in dissipation was observed. The observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide (E ) and the depth-integrated dissipation (D), such that D ϳ E 1Ϯ0.5 at sites along the ridge. This kinematic relationship is supported by combining a simple knife-edge model to estimate internal tide generation, with wave-wave interaction time scales to estimate dissipation. The along-ridge kinematic relationship and the observed vertical and cross-ridge structures are used to extrapolate the relatively sparse observations along the length of the ridge, giving an estimate of 3 Ϯ 1.5 GW of tidal energy lost to turbulence dissipation within 60 km of the ridge. This is roughly 15% of the energy estimated to be lost from the barotropic tide.
Journal of Physical Oceanography, 2003
... J. Geophys. Res., 99, 12319–12341. Dickson, RR, J. Lazier, J. Meincke, P. Rhines, and J. Swif... more ... J. Geophys. Res., 99, 12319–12341. Dickson, RR, J. Lazier, J. Meincke, P. Rhines, and J. Swift, 1996: Long-term coordinated changes in the convective activity of the North Atlantic. Progress in Oceanography, Vol. 38, Pergamon, 241–295. ...
Journal of Geophysical Research, 2011
Satellite altimetric sea surface height anomaly (SSHA) data from Geosat Follow-on (GFO) and Europ... more Satellite altimetric sea surface height anomaly (SSHA) data from Geosat Follow-on (GFO) and European Remote Sensing (ERS), as well as TOPEX/Poseidon (T/P), are merged to estimate M2 internal tides around the Hawaiian Ridge, with higher spatial resolution than ...
Deep-Sea Research Part I-Oceanographic Research Papers, 2014
The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper con... more The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean's role in climate.
This study examines water property distributions in the deep layer of the South China Sea using a... more This study examines water property distributions in the deep layer of the South China Sea using all available hydrographic data. Our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the Pacific into the South China Sea through the Luzon Strait. Applying hydraulic theory with assumptions of zero potential vorticity and flat
The overflow of dense water from the Nordic Seas through the Faroe Bank Channel (FBC) has attribu... more The overflow of dense water from the Nordic Seas through the Faroe Bank Channel (FBC) has attributes suggesting hydraulic control, including an asymmetry across the sill reminiscent of flow over a dam. However, because of the influence of the earth's rotation, as well as the presence of continuous gradients in velocity and density, the standard approach of looking for a
Journal of Geophysical Research, 2003
We report on a combined modeling and observational effort to understand the Denmark Strait Overfl... more We report on a combined modeling and observational effort to understand the Denmark Strait Overflow (DSO). Four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution. The observations reveal the mean path of the dense water, as well as the presence of strong barotropic flows, energetic variability, and strong bottom friction and
Two recent surveys of velocity, temperature and salinity in the Denmark Strait are used to charac... more Two recent surveys of velocity, temperature and salinity in the Denmark Strait are used to characterize the flo w structure, transport and dynamics of the dense overflo w from the Nordic Seas. The mean transport of dense water found at the sill is indistinguishable from measurements made in 1973 (to within 20%), and the statistics of variability are similarly identical.
Working Conference on Current Measurement, 2005
We developed an autonomous ocean profiling velocity and density float that provides exceptional v... more We developed an autonomous ocean profiling velocity and density float that provides exceptional vertical coverage and temporal resolution to depths of 2000 m for deployments of many years. Electrodes were added to the exterior of standard WRC APEX floats, and electronics were added inside. The electrode voltages result from the motion of seawater and the instrument through the Earth's magnetic
Journal of Physical Oceanography
An integrated analysis of turbulence observations from four unique instrument platforms obtained ... more An integrated analysis of turbulence observations from four unique instrument platforms obtained over the Hawaiian Ridge leads to an assessment of the vertical, cross-ridge, and along-ridge structure of turbulence dissipation rate and diffusivity. The diffusivity near the seafloor was, on average, 15 times that in the midwater column. At 1000-m depth, the diffusivity atop the ridge was 30 times that 10 km off the ridge, decreasing to background oceanic values by 60 km. A weak (factor of 2) spring-neap variation in dissipation was observed. The observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide (E ) and the depth-integrated dissipation (D), such that D ϳ E 1Ϯ0.5 at sites along the ridge. This kinematic relationship is supported by combining a simple knife-edge model to estimate internal tide generation, with wave-wave interaction time scales to estimate dissipation. The along-ridge kinematic relationship and the observed vertical and cross-ridge structures are used to extrapolate the relatively sparse observations along the length of the ridge, giving an estimate of 3 Ϯ 1.5 GW of tidal energy lost to turbulence dissipation within 60 km of the ridge. This is roughly 15% of the energy estimated to be lost from the barotropic tide.
Journal of Physical Oceanography, 2015
Deep-Sea Research Part I-Oceanographic Research Papers, 2014
The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper con... more The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean's role in climate.
In ONR's CBLAST Hurricane research program observations were made of the upper ocean's re... more In ONR's CBLAST Hurricane research program observations were made of the upper ocean's response to Hurricane Frances. Three EM-APEX floats (velocity sensing versions of Webb Research APEX floats) and two Lagrangian floats were deployed north of Hispaniola from a C-130 aircraft ahead of Hurricane Frances in September 2004. The EM-APEX floats measured T, S and V over the upper 500
Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society, 2010
Turbulent diapycnal mixing in the ocean controls the transport of heat, freshwater, dissolved gas... more Turbulent diapycnal mixing in the ocean controls the transport of heat, freshwater, dissolved gases, nutrients, and pollutants. Though many present generation climate models represent turbulent mixing with a simplistic diffusivity below the surface mixed layer, the last two decades of ocean mixing research have instead revealed dramatic spatial and temporal heterogeneity in ocean mixing. Climate models that do not appropriately represent the turbulent fluxes of heat, momentum, and CO2 across critical interfaces will not accurately represent the ocean's role in present or future climate. An accurate picture of the worldwide geography of mixing requires a vastly increased database of observations. Unfortunately, traditional microstructure estimates of turbulent mixing are expensive, difficult, and rare. A key development of the last decade has been the development of tools to estimate the turbulent mixing rate from finescale (order 10-50 meter resolution) measurements of internal-wave shear and vertical strain. Global arrays such as the Argo program provide an unprecedented and as yet underdeveloped opportunity to define the global internal wave climate, and in turn identify mixing patterns and hotspots.
Journal of Physical Oceanography, 2006
... Girton, James B., Lawrence J. Pratt, David A. Sutherland, James F. Price, 2006: Is the Faroe ... more ... Girton, James B., Lawrence J. Pratt, David A. Sutherland, James F. Price, 2006: Is the Faroe Bank Channel Overflow Hydraulically Controlled?. J. Phys. Oceanogr., 36, 23402349. ... Is the Faroe Bank Channel Overflow Hydraulically Controlled? James B. Girton ...
Oceanography, 2011
... Authors. James B. Girton Applied Physics Laboratory, University of Washington, Seattle, WA, U... more ... Authors. James B. Girton Applied Physics Laboratory, University of Washington, Seattle, WA, USA. ... Geophysical Research Letters 34, L24601. [CrossRef]. Arango, HG, JC Levin, EN Curchitser, B. Zhang, AM Moore, W. Han, AL Gordon, CM Lee, and JB Girton. 2011. ...
Ocean Modelling, 2006
A series of idealised numerical simulations of dense water flowing down a broad uniform slope are... more A series of idealised numerical simulations of dense water flowing down a broad uniform slope are presented, employing both a z-coordinate model (the MIT general circulation model) and an isopycnal coordinate model (the Hallberg Isopycnal Model). Calculations are carried out at several different horizontal and vertical resolutions, and for a range of physical parameters. A subset of calculations are carried out at very high resolution using the non-hydrostatic variant of the MITgcm. In all calculations dense water descends the slope while entraining and mixing with ambient fluid. The dependence of entrainment, mixing and down-slope descent on resolution and vertical coordinate are assessed. At very coarse resolutions the z-coordinate model generates excessive spurious mixing, and dense water has difficulty descending the slope. However, at intermediate resolutions the mixing in the z-coordinate model is less than found in the high-resolution non-hydrostatic simulations, and dense water descends further down the slope. Iso-1463-5003/$ -see front matter Ó
Journal of Physical Oceanography, 2011
... JB Girton ... Invaluable assistance with the work was provided by Ryan Abernathy, Larry Ander... more ... JB Girton ... Invaluable assistance with the work was provided by Ryan Abernathy, Larry Anderson, Angel Ruiz Angulo, Magdalena Carranza, David Ciochetto, Gillian Damerell, Ken Decoteau, Catherine Grendi, Brian Guest, Jay Hooper, Leah Houghton, Byron Kilbourne, Valery ...
Journal of Physical Oceanography, 2006
An integrated analysis of turbulence observations from four unique instrument platforms obtained ... more An integrated analysis of turbulence observations from four unique instrument platforms obtained over the Hawaiian Ridge leads to an assessment of the vertical, cross-ridge, and along-ridge structure of turbulence dissipation rate and diffusivity. The diffusivity near the seafloor was, on average, 15 times that in the midwater column. At 1000-m depth, the diffusivity atop the ridge was 30 times that 10 km off the ridge, decreasing to background oceanic values by 60 km. A weak (factor of 2) spring-neap variation in dissipation was observed. The observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide (E ) and the depth-integrated dissipation (D), such that D ϳ E 1Ϯ0.5 at sites along the ridge. This kinematic relationship is supported by combining a simple knife-edge model to estimate internal tide generation, with wave-wave interaction time scales to estimate dissipation. The along-ridge kinematic relationship and the observed vertical and cross-ridge structures are used to extrapolate the relatively sparse observations along the length of the ridge, giving an estimate of 3 Ϯ 1.5 GW of tidal energy lost to turbulence dissipation within 60 km of the ridge. This is roughly 15% of the energy estimated to be lost from the barotropic tide.
Journal of Physical Oceanography, 2003
... J. Geophys. Res., 99, 12319–12341. Dickson, RR, J. Lazier, J. Meincke, P. Rhines, and J. Swif... more ... J. Geophys. Res., 99, 12319–12341. Dickson, RR, J. Lazier, J. Meincke, P. Rhines, and J. Swift, 1996: Long-term coordinated changes in the convective activity of the North Atlantic. Progress in Oceanography, Vol. 38, Pergamon, 241–295. ...
Journal of Geophysical Research, 2011
Satellite altimetric sea surface height anomaly (SSHA) data from Geosat Follow-on (GFO) and Europ... more Satellite altimetric sea surface height anomaly (SSHA) data from Geosat Follow-on (GFO) and European Remote Sensing (ERS), as well as TOPEX/Poseidon (T/P), are merged to estimate M2 internal tides around the Hawaiian Ridge, with higher spatial resolution than ...