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Papers by thomas whitworth

Journal of Physical Oceanography, Jun 1, 1985

ABSTRACT A 20-year long volume transport time series of the Antarctic Circumpolar Current across ... more ABSTRACT A 20-year long volume transport time series of the Antarctic Circumpolar Current across the Drake Passage is estimated from the combination of information from in situ current meter data (2006-2009) and satellite altimetry data (1992-2012). A new method for transport estimates had to be designed. It accounts for the dependence of the vertical velocity structure on surface velocity and latitude. Yet unpublished velocity profile time series from Acoustic Doppler Current Profilers are used to provide accurate vertical structure estimates in the upper 350 m. The mean cross-track surface geostrophic velocities are estimated using an iterative error/correction scheme to the mean velocities deduced from two recent mean dynamic topographies. The internal consistency and the robustness of the method are carefully assessed. Comparisons with independent data demonstrate the accuracy of the method.The full-depth volume transport has a mean of 141 Sv (standard error of the mean 2.7 Sv), a standard deviation (std) of 13 Sv and a range of 110 Sv. Yearly means vary from 133.6 Sv in 2011 to 150 Sv in 1993 and standard deviations from 8.8 Sv in 2009 to 17.9 Sv in 1995. The canonical ISOS values (mean 133.8 Sv, std 11.2 Sv) obtained from a year-long record in 1979 are very similar to those found here for year 2011 (133.6 Sv and 12 Sv). Full-depth transports and transports over 3000 m barely differ as in that particular region of Drake Passage the deep recirculations in two semi-closed basins have a close to zero net transport.

Journal of Physical Oceanography, Oct 30, 1977

J Phys Oceanogr, 1979

Current and temperature records from 10 meters on six year-long moorings deployed during February... more Current and temperature records from 10 meters on six year-long moorings deployed during February 1975 in Drake Passage are examined and discussed in the context of hydrographic data from that area. The mean flow directions are consistent with those from geopotential ...

Journal of Physical Oceanography, Sep 1, 1982

... The agreement between directly-measured and baroclinic shears is generally good except in reg... more ... The agreement between directly-measured and baroclinic shears is generally good except in regions of large bathymetric relief and during periods when current cores were shifting past or between moorings. ... Cited by. Shenfu Dong, Silvia Garzoli, Molly Baringer. ...

Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science... more Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0967-0637/94 $7.00 + 0.00 NOTE Slight northwestward inflow to the deep South Fiji Basin BRUCE A. WARREN,* THOMAS ...

Journal of Physical Oceanography, 1977

Journal of Physical Oceanography, 1979

Current and temperature records from 10 meters on six year-long moorings deployed during February... more Current and temperature records from 10 meters on six year-long moorings deployed during February 1975 in Drake Passage are examined and discussed in the context of hydrographic data from that area. The mean flow directions are consistent with those from geopotential ...

Journal of Marine Research, 1993

... The importance of the Scotia Sea on the outflow of Weddell Sea Deep Water by Ricardo A. Lucar... more ... The importance of the Scotia Sea on the outflow of Weddell Sea Deep Water by Ricardo A. Lucarnini,' Thomas Whitworth III' and Worth D. Nowlin, Jr.' ... Deep Water. Because it is filled with recently ventilated Weddell Sea Deep Water, the Scotia Sea is important to both influences. ...

Journal of Geophysical Research, 1991

Fourteen-month velocity and temperature records from an array of 14 moorings north and west of th... more Fourteen-month velocity and temperature records from an array of 14 moorings north and west of the Falkland Plateau and supporting hydrographic and tracer data reveal a narrow boundary current that carries dense Antarctic waters. The current flows west along the northern flank of the Falkland Plateau with mean speeds of more than 10 cm s-1 at 5000 m and more

Journal of Geophysical Research, 1987

Process, ASSP-35 :917-926. Josse, Fabien, 1987. Analysis of the amplification and convolution of ... more Process, ASSP-35 :917-926. Josse, Fabien, 1987. Analysis of the amplification and convolution of reflected bulk acoustic waves in a piezoelectric/semieonductor structure. J. acoust. Soc. Am., 81(6):176%1774.

Journal of Geophysical Research, 1987

Journal of Geophysical Research, 1985

Yearlong measurements of current and temperature are used to examine the characteristics of eddy ... more Yearlong measurements of current and temperature are used to examine the characteristics of eddy heat flux and its distribution in Drake Passage. This seemingly straightforward calculation can produce misleading results when measurement errors are not corrected and when careful consideration is not given to the nature of the time series under study and the coordinate system used. When moorings blow over during periods of high current speeds, eddy heat fluxes produced from the resulting records may be overestimated by as much as 20% if not corrected by using concomitant pressure time series and vertical temperature gradients. Although short-time-scale processes (such as tides, internal waves, and inertial oscillations) are routinely eliminated from heat flux estimates by low-pass filtering, low-frequency contamination of eddy heat fluxes is not usually considered. Long-period events can impose unwanted, dominating cross correlation (eddy heat flux) between fluctuation temperature and velocity. In Drake Passage, low-frequency variability in some current records is associated with sporadic lateral shifts of the fronts within the Antarctic Circumpolar Current. Defining an effective eddy time scale (40 hours to 90 days) and band-passing the current records before calculating eddy heat flux results in values that are more homogeneous (consistent with one another) in direction and have higher statistical significance. Finally, we consider the coordinate system used for the eddy heat flux calculations relative to the dynamic processes under study. For the Circumpolar Current we define "poleward" eddy heat flux as that component perpendicular to the axis of the current that forms a continuous, but distorted, band encircling Antarctica. Since the current direction varies in time, across-stream eddy heat flux is calculated relative to the 90-day low-pass direction. The resulting heat fluxes from all deep instruments are small (about 1 kW/m2), whereas those at depths less than 1000 m in the northern passage are an order of magnitude larger. The average across-stream flux for all available instruments is 3.7 kW/m 2 and directed to the right (poleward) of the 90-day low-pass current. Cospectra of fluctuation temperature and velocity show that heat flux is separated, on the average, into two frequency bands with corresponding periods between 100 and 40 days and 16 and 10 days. This pattern is strongly influenced by the records from shallow instruments and those in the northern passage and compares favorably with the cospectrum from a 5-year bridged record from the central passage. Comparison with previous estimates in this region shows considerable differences, partly as a result of the use of different techniques. However, analysis of five 1-year records from a single location shows that interannual variability is large, which urges caution when interpreting the significance of isolated short-term estimates of eddy heat flux.

Journal of Geophysical Research, 1985

The fronts and water mass zones comprising the Antarctic Circumpolar Current at Drake Passage hav... more The fronts and water mass zones comprising the Antarctic Circumpolar Current at Drake Passage have associated with them characteristic temperature structures. This property is used to construct maps that depict changes in the location of the fronts at 500 m. The zonation maps are based on temperature and velocity data obtained from 15 moorings deployed in the northern and central Drake Passage as part of the International Southern Ocean Studies experiment DRAKE 79. They provide a description of the flow of the Antarctic Circumpolar Current through Drake Passage at weekly intervals for a period of 1 year' January 1979 to January 1980. Mesoscale activity in central Drake Passage was dominated by the migration of three cold-core rings and one warm-core ring. The cold-core rings formed from northward extending meanders of the Polar Front; the warm-core ring from a southward extending meander of the Subantarctic Front. All four rings appeared to form within Drake Passage and to follow similar trajectories, which were influenced by local bathymetry. Variations in the location of the Subantarctic and Polar fronts were caused by meanders. In the narrowest portion of Drake Passage, when rings are present in the Polar Frontal Zone, the Polar Front is found farther south than when rings are absent.

Journal of Geophysical Research, 1989

The two principal fronts within the Antarctic Circumpolar Current (ACC), the Subantarctic Front (... more The two principal fronts within the Antarctic Circumpolar Current (ACC), the Subantarctic Front (SAF) and the Polar Front (PF), are investigated with respect to their spatial patterns and relations to deep water masses from the northern Drake Passage to the western and southern Argentine Basin. Observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters. East of Drake Passage, the width of the Polar Frontal Zone (PFZ) increases rapidly when the SAF turns sharply northward as a part of the Falkland (Malvinas) Current, while the PF remains oriented mainly toward the northeast. Found within this region of the PFZ are mesoscale eddies, the upper layers of which consist of Subantarctic Mode Water from the Pacific. The contrasts in upper layer water properties that identify the SAF can be traced the entire length of the Falkland Current to the Brazil-Falkland confluence zone and then southward to the southern Argentine Basin. There the SAF turns eastward and later, but perhaps not always, merges with the PF north of Ewing Bank to form a single, intense current core strongly influenced by bottom topography. At times this eastward current loops southward through a gap in the Falkland Ridge into the Georgia Basin, thereby supplying relatively warm and salty Subantarctic water to the Antarctic Zone. East of the gap, the two fronts become separated and are once again distinct features in the vicinity of the Islas Orcadas Rise. At depth, within Drake Passage and the western Scotia Sea, the SAF and PF are not lateral boundaries between distinct water masses, but are instead identified by enhanced vertical displacements of property isopleths. With the northward turn of the SAF east of Drake Passage, a thick layer of Circumpolar Deep Water (CDW) is advected over the Falkland Plateau into the Argentine Basin. There it is joined by waters entering the Argentine Basin via a deep spreading route through the Georgia Basin: denser CDW, deep water from the Weddell Sea, and episodically, deep water from the southeastern Pacific Ocean. Together, these waters form a northward flow off the Patagonian shelf that extends from the sea surface to the bottom, most of which turns back toward the south with the Falkland Current return. Also flowing south, along the seaward side of the Falkland Current return well away from the western boundary, is the main core of North Atlantic Deep Water (NADW). Detatched masses of NADW are observed within the CDW at the western boundary as well as within the ACC south of the SAF in the south central Argentine Basin. 1.

Geophysical Research Letters, 2004

Geophysical Research Letters, 2006

Geophysical Research Letters, 2003

Deep Sea Research Part II: Topical Studies in Oceanography, 2002

Current meters moored for 19.5 months at Lat. 201S in the deep water of the western Mascarene Bas... more Current meters moored for 19.5 months at Lat. 201S in the deep water of the western Mascarene Basin recorded a distinct, large-amplitude ½Oð10 cm s À1 Þ undulation of bimonthly period, propagating westward at 7 cm s À1 : Its characteristics demonstrate that it was a barotropic Rossby wave of relatively large meridional scale. Simple theory accounts for it as having been forced by local wind-stress curl at one of the resonant frequencies of the Mascarene Basin. A sharp bimonthly peak is also prominent in spectra of TOPEX/POSEIDON sea-surface height in the Mascarene Basin, but is not seen to the eastward, as is consistent with the local generation. Fluctuations of 45-day period reported earlier in the upper ocean just northeast of Madagascar might have been generated through a similar process, but with frequency shifted by the South Equatorial Current. r

Deep Sea Research Part I: Oceanographic Research Papers, 1993

The availability of new, high-quality, hydrographic data has prompted a re-examination of the cir... more The availability of new, high-quality, hydrographic data has prompted a re-examination of the circulation in the Atlantic sector of the Southern Ocean. Dynamic topography maps and tracer distributions on selected isopycnal surfaces show that the Weddell

Deep Sea Research Part I: Oceanographic Research Papers, 1994

Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science... more Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0967-0637/94 $7.00 + 0.00 NOTE Slight northwestward inflow to the deep South Fiji Basin BRUCE A. WARREN,* THOMAS ...

Journal of Physical Oceanography, Jun 1, 1985

ABSTRACT A 20-year long volume transport time series of the Antarctic Circumpolar Current across ... more ABSTRACT A 20-year long volume transport time series of the Antarctic Circumpolar Current across the Drake Passage is estimated from the combination of information from in situ current meter data (2006-2009) and satellite altimetry data (1992-2012). A new method for transport estimates had to be designed. It accounts for the dependence of the vertical velocity structure on surface velocity and latitude. Yet unpublished velocity profile time series from Acoustic Doppler Current Profilers are used to provide accurate vertical structure estimates in the upper 350 m. The mean cross-track surface geostrophic velocities are estimated using an iterative error/correction scheme to the mean velocities deduced from two recent mean dynamic topographies. The internal consistency and the robustness of the method are carefully assessed. Comparisons with independent data demonstrate the accuracy of the method.The full-depth volume transport has a mean of 141 Sv (standard error of the mean 2.7 Sv), a standard deviation (std) of 13 Sv and a range of 110 Sv. Yearly means vary from 133.6 Sv in 2011 to 150 Sv in 1993 and standard deviations from 8.8 Sv in 2009 to 17.9 Sv in 1995. The canonical ISOS values (mean 133.8 Sv, std 11.2 Sv) obtained from a year-long record in 1979 are very similar to those found here for year 2011 (133.6 Sv and 12 Sv). Full-depth transports and transports over 3000 m barely differ as in that particular region of Drake Passage the deep recirculations in two semi-closed basins have a close to zero net transport.

Journal of Physical Oceanography, Oct 30, 1977

J Phys Oceanogr, 1979

Current and temperature records from 10 meters on six year-long moorings deployed during February... more Current and temperature records from 10 meters on six year-long moorings deployed during February 1975 in Drake Passage are examined and discussed in the context of hydrographic data from that area. The mean flow directions are consistent with those from geopotential ...

Journal of Physical Oceanography, Sep 1, 1982

... The agreement between directly-measured and baroclinic shears is generally good except in reg... more ... The agreement between directly-measured and baroclinic shears is generally good except in regions of large bathymetric relief and during periods when current cores were shifting past or between moorings. ... Cited by. Shenfu Dong, Silvia Garzoli, Molly Baringer. ...

Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science... more Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0967-0637/94 $7.00 + 0.00 NOTE Slight northwestward inflow to the deep South Fiji Basin BRUCE A. WARREN,* THOMAS ...

Journal of Physical Oceanography, 1977

Journal of Physical Oceanography, 1979

Current and temperature records from 10 meters on six year-long moorings deployed during February... more Current and temperature records from 10 meters on six year-long moorings deployed during February 1975 in Drake Passage are examined and discussed in the context of hydrographic data from that area. The mean flow directions are consistent with those from geopotential ...

Journal of Marine Research, 1993

... The importance of the Scotia Sea on the outflow of Weddell Sea Deep Water by Ricardo A. Lucar... more ... The importance of the Scotia Sea on the outflow of Weddell Sea Deep Water by Ricardo A. Lucarnini,' Thomas Whitworth III' and Worth D. Nowlin, Jr.' ... Deep Water. Because it is filled with recently ventilated Weddell Sea Deep Water, the Scotia Sea is important to both influences. ...

Journal of Geophysical Research, 1991

Fourteen-month velocity and temperature records from an array of 14 moorings north and west of th... more Fourteen-month velocity and temperature records from an array of 14 moorings north and west of the Falkland Plateau and supporting hydrographic and tracer data reveal a narrow boundary current that carries dense Antarctic waters. The current flows west along the northern flank of the Falkland Plateau with mean speeds of more than 10 cm s-1 at 5000 m and more

Journal of Geophysical Research, 1987

Process, ASSP-35 :917-926. Josse, Fabien, 1987. Analysis of the amplification and convolution of ... more Process, ASSP-35 :917-926. Josse, Fabien, 1987. Analysis of the amplification and convolution of reflected bulk acoustic waves in a piezoelectric/semieonductor structure. J. acoust. Soc. Am., 81(6):176%1774.

Journal of Geophysical Research, 1987

Journal of Geophysical Research, 1985

Yearlong measurements of current and temperature are used to examine the characteristics of eddy ... more Yearlong measurements of current and temperature are used to examine the characteristics of eddy heat flux and its distribution in Drake Passage. This seemingly straightforward calculation can produce misleading results when measurement errors are not corrected and when careful consideration is not given to the nature of the time series under study and the coordinate system used. When moorings blow over during periods of high current speeds, eddy heat fluxes produced from the resulting records may be overestimated by as much as 20% if not corrected by using concomitant pressure time series and vertical temperature gradients. Although short-time-scale processes (such as tides, internal waves, and inertial oscillations) are routinely eliminated from heat flux estimates by low-pass filtering, low-frequency contamination of eddy heat fluxes is not usually considered. Long-period events can impose unwanted, dominating cross correlation (eddy heat flux) between fluctuation temperature and velocity. In Drake Passage, low-frequency variability in some current records is associated with sporadic lateral shifts of the fronts within the Antarctic Circumpolar Current. Defining an effective eddy time scale (40 hours to 90 days) and band-passing the current records before calculating eddy heat flux results in values that are more homogeneous (consistent with one another) in direction and have higher statistical significance. Finally, we consider the coordinate system used for the eddy heat flux calculations relative to the dynamic processes under study. For the Circumpolar Current we define "poleward" eddy heat flux as that component perpendicular to the axis of the current that forms a continuous, but distorted, band encircling Antarctica. Since the current direction varies in time, across-stream eddy heat flux is calculated relative to the 90-day low-pass direction. The resulting heat fluxes from all deep instruments are small (about 1 kW/m2), whereas those at depths less than 1000 m in the northern passage are an order of magnitude larger. The average across-stream flux for all available instruments is 3.7 kW/m 2 and directed to the right (poleward) of the 90-day low-pass current. Cospectra of fluctuation temperature and velocity show that heat flux is separated, on the average, into two frequency bands with corresponding periods between 100 and 40 days and 16 and 10 days. This pattern is strongly influenced by the records from shallow instruments and those in the northern passage and compares favorably with the cospectrum from a 5-year bridged record from the central passage. Comparison with previous estimates in this region shows considerable differences, partly as a result of the use of different techniques. However, analysis of five 1-year records from a single location shows that interannual variability is large, which urges caution when interpreting the significance of isolated short-term estimates of eddy heat flux.

Journal of Geophysical Research, 1985

The fronts and water mass zones comprising the Antarctic Circumpolar Current at Drake Passage hav... more The fronts and water mass zones comprising the Antarctic Circumpolar Current at Drake Passage have associated with them characteristic temperature structures. This property is used to construct maps that depict changes in the location of the fronts at 500 m. The zonation maps are based on temperature and velocity data obtained from 15 moorings deployed in the northern and central Drake Passage as part of the International Southern Ocean Studies experiment DRAKE 79. They provide a description of the flow of the Antarctic Circumpolar Current through Drake Passage at weekly intervals for a period of 1 year' January 1979 to January 1980. Mesoscale activity in central Drake Passage was dominated by the migration of three cold-core rings and one warm-core ring. The cold-core rings formed from northward extending meanders of the Polar Front; the warm-core ring from a southward extending meander of the Subantarctic Front. All four rings appeared to form within Drake Passage and to follow similar trajectories, which were influenced by local bathymetry. Variations in the location of the Subantarctic and Polar fronts were caused by meanders. In the narrowest portion of Drake Passage, when rings are present in the Polar Frontal Zone, the Polar Front is found farther south than when rings are absent.

Journal of Geophysical Research, 1989

The two principal fronts within the Antarctic Circumpolar Current (ACC), the Subantarctic Front (... more The two principal fronts within the Antarctic Circumpolar Current (ACC), the Subantarctic Front (SAF) and the Polar Front (PF), are investigated with respect to their spatial patterns and relations to deep water masses from the northern Drake Passage to the western and southern Argentine Basin. Observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters. East of Drake Passage, the width of the Polar Frontal Zone (PFZ) increases rapidly when the SAF turns sharply northward as a part of the Falkland (Malvinas) Current, while the PF remains oriented mainly toward the northeast. Found within this region of the PFZ are mesoscale eddies, the upper layers of which consist of Subantarctic Mode Water from the Pacific. The contrasts in upper layer water properties that identify the SAF can be traced the entire length of the Falkland Current to the Brazil-Falkland confluence zone and then southward to the southern Argentine Basin. There the SAF turns eastward and later, but perhaps not always, merges with the PF north of Ewing Bank to form a single, intense current core strongly influenced by bottom topography. At times this eastward current loops southward through a gap in the Falkland Ridge into the Georgia Basin, thereby supplying relatively warm and salty Subantarctic water to the Antarctic Zone. East of the gap, the two fronts become separated and are once again distinct features in the vicinity of the Islas Orcadas Rise. At depth, within Drake Passage and the western Scotia Sea, the SAF and PF are not lateral boundaries between distinct water masses, but are instead identified by enhanced vertical displacements of property isopleths. With the northward turn of the SAF east of Drake Passage, a thick layer of Circumpolar Deep Water (CDW) is advected over the Falkland Plateau into the Argentine Basin. There it is joined by waters entering the Argentine Basin via a deep spreading route through the Georgia Basin: denser CDW, deep water from the Weddell Sea, and episodically, deep water from the southeastern Pacific Ocean. Together, these waters form a northward flow off the Patagonian shelf that extends from the sea surface to the bottom, most of which turns back toward the south with the Falkland Current return. Also flowing south, along the seaward side of the Falkland Current return well away from the western boundary, is the main core of North Atlantic Deep Water (NADW). Detatched masses of NADW are observed within the CDW at the western boundary as well as within the ACC south of the SAF in the south central Argentine Basin. 1.

Geophysical Research Letters, 2004

Geophysical Research Letters, 2006

Geophysical Research Letters, 2003

Deep Sea Research Part II: Topical Studies in Oceanography, 2002

Current meters moored for 19.5 months at Lat. 201S in the deep water of the western Mascarene Bas... more Current meters moored for 19.5 months at Lat. 201S in the deep water of the western Mascarene Basin recorded a distinct, large-amplitude ½Oð10 cm s À1 Þ undulation of bimonthly period, propagating westward at 7 cm s À1 : Its characteristics demonstrate that it was a barotropic Rossby wave of relatively large meridional scale. Simple theory accounts for it as having been forced by local wind-stress curl at one of the resonant frequencies of the Mascarene Basin. A sharp bimonthly peak is also prominent in spectra of TOPEX/POSEIDON sea-surface height in the Mascarene Basin, but is not seen to the eastward, as is consistent with the local generation. Fluctuations of 45-day period reported earlier in the upper ocean just northeast of Madagascar might have been generated through a similar process, but with frequency shifted by the South Equatorial Current. r

Deep Sea Research Part I: Oceanographic Research Papers, 1993

The availability of new, high-quality, hydrographic data has prompted a re-examination of the cir... more The availability of new, high-quality, hydrographic data has prompted a re-examination of the circulation in the Atlantic sector of the Southern Ocean. Dynamic topography maps and tracer distributions on selected isopycnal surfaces show that the Weddell

Deep Sea Research Part I: Oceanographic Research Papers, 1994

Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science... more Pergamon Deep-Sea Research I, Vol. 41, No. 5/6, pp. 953-956, 1994 Copyright 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0967-0637/94 $7.00 + 0.00 NOTE Slight northwestward inflow to the deep South Fiji Basin BRUCE A. WARREN,* THOMAS ...