measuring the eastern boundary inflow to the labrador sea outline 1. insights on the overturning...
TRANSCRIPT
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Measuring the eastern boundary inflow Measuring the eastern boundary inflow to the Labrador Sea to the Labrador Sea
Measuring the eastern boundary inflow Measuring the eastern boundary inflow to the Labrador Sea to the Labrador Sea
Outline
1. Insights on the overturning circulation of the Labrador Sea
2. Challenges associated with measuring the eastern boundary current
3. Strawman array design and remaining questions
Greenland coast viewed from R/V Knorr , Oct 2008 Greenland coast viewed from R/V Knorr , Oct 2008
(Photo by Ben Harden)(Photo by Ben Harden)
Robert S. Pickart (WHOI)
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Labrador Sea general circulation
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Wintertime storm tracks (from 45 years of ECMWF re-analysis data) Wintertime storm tracks (from 45 years of ECMWF re-analysis data)
VVååge et al. (2009) ge et al. (2009)
Mean storm track
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Heat loss from wintertime cold-air outbreaks Heat loss from wintertime cold-air outbreaks
Color = heat loss in Watts/mColor = heat loss in Watts/m22 (from NCEP reanalysis) (from NCEP reanalysis) Ice
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Heat loss from wintertime cold-air outbreaks Heat loss from wintertime cold-air outbreaks
Color = heat loss in Watts/mColor = heat loss in Watts/m22 (from NCEP reanalysis) (from NCEP reanalysis)
Contours = Absolute geostrophic Contours = Absolute geostrophic pressure (Lavender et al. (2000) pressure (Lavender et al. (2000)
Ice
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Surface eddy speed Surface eddy speed
After Lilly et al. (2003) After Lilly et al. (2003)
Color = surface eddy Color = surface eddy speed (cm/s) speed (cm/s)
Contours = Absolute geostrophic Contours = Absolute geostrophic pressure (Lavender et al. (2000) pressure (Lavender et al. (2000)
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Surface eddy speed and regions of deep convection Surface eddy speed and regions of deep convection
Color = surface eddy Color = surface eddy speed (cm/s) speed (cm/s)
Contours = Absolute geostrophic Contours = Absolute geostrophic pressure (Lavender et al. (2000) pressure (Lavender et al. (2000)
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Surface eddy speed and regions of deep convection Surface eddy speed and regions of deep convection
Color = surface eddy Color = surface eddy speed (cm/s) speed (cm/s)
Contours = Absolute geostrophic Contours = Absolute geostrophic pressure (Lavender et al. (2000) pressure (Lavender et al. (2000)
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Mixed-layer depth in winter 1997 Mixed-layer depth in winter 1997
Color = mixed layer depth (m) Color = mixed layer depth (m)
Contours = Absolute geostrophic Contours = Absolute geostrophic pressure (Lavender et al. (2000) pressure (Lavender et al. (2000)
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WOCE AR7W lineInverse calculation
AR7W AR7W
Time period of high NAO in the early to mid 1990s
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Float data
Mean circulation at 700m 1995Mean circulation at 700m 1995–19–1999 99
Lavendar et al. (2000) Lavendar et al. (2000)
AR7WAR7W
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Referencing the geostrophic velocity section
Mean velocity at 700m from PALACE Mean velocity at 700m from PALACE
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Referencing the geostrophic velocity section
Mean velocity at 700m from PALACE Mean velocity at 700m from PALACE
Mean temperature/density section Mean temperature/density section
X
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Referencing the geostrophic velocity section
Mean velocity at 700m from PALACE Mean velocity at 700m from PALACE
Mean temperature/density section Mean temperature/density section
X
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Referencing the geostrophic velocity section
Mean velocity at 700m from PALACE Mean velocity at 700m from PALACE
Mean temperature/density section Mean temperature/density section
X
Total transport in: 35.4 SvTotal transport in: 35.4 SvTotal transport out: 35.5 SvTotal transport out: 35.5 Sv
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Absolute geostrophic velocity
AR7W AR7W
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Absolute geostrophic velocity
Total Boundary Current transport = 28.5 Sv Total Boundary Current transport = 28.5 Sv
Recirculation transport = 2.5 Sv Recirculation transport = 2.5 Sv
Overflow water transport = 12.4 Sv Overflow water transport = 12.4 Sv Throughput
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Absolute geostrophic velocity
Total Boundary Current transport = 28.5 Sv Total Boundary Current transport = 28.5 Sv
Recirculation transport = 2.5 Sv Recirculation transport = 2.5 Sv
Overflow water transport = 12.4 Sv Overflow water transport = 12.4 Sv Throughput
Near zeroNear zerovelocity! velocity!
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Depth space: Overturning and horizontal components of the flow
Decompose the full velocity: Decompose the full velocity:
Then decompose the deviation velocity: Then decompose the deviation velocity:
),(')(),( zxvzvzxv x
),(~)('),(' zxvxvzxv z
Overturning Overturning Deviation Deviation
Horizontal gyre
Horizontal gyre
Baroclinic gyre
Baroclinic gyre
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Transport components
Overturning Cell Overturning Cell
Horizontal cell Horizontal cell
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Transport components
95% of sinking happens 95% of sinking happens
in boundary current in boundary current
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Density space: Overturning transport
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Density space: Overturning transport
> 95% of the transport imbalance > 95% of the transport imbalance occurs in the boundary current occurs in the boundary current
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What are the important points for OSNAP? What are the important points for OSNAP?
Seaward of the 700m isobath there is mass balance across Seaward of the 700m isobath there is mass balance across the section (i.e. excluding the shallow shelf-edge flows). the section (i.e. excluding the shallow shelf-edge flows).
The horizontal cell is significantly larger than the overturning cell. The horizontal cell is significantly larger than the overturning cell.
Nearly all of the overturning, in depth space and density space,Nearly all of the overturning, in depth space and density space,occurs along the rim of the basin. Flows in the middle of theoccurs along the rim of the basin. Flows in the middle of theBasin are weak.Basin are weak.
There is substantial mesoscale variability, so low-passing will be There is substantial mesoscale variability, so low-passing will be necessary. necessary.
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Ongoing Timeseries in the Labrador Sea Ongoing Timeseries in the Labrador Sea
OSNAP-east moorings
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Ongoing Timeseries in the Labrador Sea Ongoing Timeseries in the Labrador Sea
OSNAP-east moorings
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
1997 hydrographicSections
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Two eastern boundary Two eastern boundary crossings in Feb 1997crossings in Feb 1997
Salinity (color) overlain Salinity (color) overlain by density (contours) by density (contours)
North North
South South
16 Feb 16 Feb
26 Feb 26 Feb
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
2001 hydrographic Section
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Eastern boundary crossing Eastern boundary crossing in Aug 2001 in Aug 2001
Salinity (color) overlain bySalinity (color) overlain bydensity (contours) density (contours)
Absolute geostrophic velocity (color) Absolute geostrophic velocity (color) overlain by density (contours) overlain by density (contours)
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Eastern boundary crossing Eastern boundary crossing in Aug 2001 in Aug 2001
Salinity (color) overlain bySalinity (color) overlain bydensity (contours) density (contours)
Absolute geostrophic velocity (color) Absolute geostrophic velocity (color) overlain by density (contours) overlain by density (contours)
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Eastern boundary crossing in Aug 2001 Eastern boundary crossing in Aug 2001
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Eastern boundary crossing in Aug 2001 Eastern boundary crossing in Aug 2001
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
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Eastern boundary crossing in Aug 2001 Eastern boundary crossing in Aug 2001
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Eastern boundary crossing in Aug 2001 Eastern boundary crossing in Aug 2001
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Eastern boundary crossing in Aug 2001 Eastern boundary crossing in Aug 2001
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Eastern boundary crossing in Aug 2001 Eastern boundary crossing in Aug 2001
Use of current meters and Microcats is safer and allows for 2-year deployments
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Strawman OSNAP-West Boundary Arrays Strawman OSNAP-West Boundary Arrays
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Remaining issues: shelf, near-surface, recirculation Remaining issues: shelf, near-surface, recirculation
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Remaining issues: shelf, near-surface, recirculation Remaining issues: shelf, near-surface, recirculation
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Considerations for OSNAP eastern boundary array Considerations for OSNAP eastern boundary array
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Positive aspects of eastern array location Positive aspects of eastern array location
Bottom topography is gentle enough to effectively resolve Bottom topography is gentle enough to effectively resolve the boundary current. the boundary current.
Array will coincide with an altimeter line (providing additional Array will coincide with an altimeter line (providing additional surface velocity information). surface velocity information).
By moving south, the array is a true input boundary condition forBy moving south, the array is a true input boundary condition forthe Labrador Sea (to compare to the western export array). the Labrador Sea (to compare to the western export array).
The offshore recirculation is geographically confined, which The offshore recirculation is geographically confined, which means it can be effectively sampled with floats. means it can be effectively sampled with floats.
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Negative aspects of eastern array location Negative aspects of eastern array location
It is not the AR7W line! (which provides a wonderful context). It is not the AR7W line! (which provides a wonderful context).
Logistically more difficult to service the array.Logistically more difficult to service the array.
Closer to OSNAP Cape Farewell array (less contrast). Closer to OSNAP Cape Farewell array (less contrast).