Monitoring of the MOC

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Monitoring of the MOC (MOVE) with
T. Kanzow C. Begler M. Lankhorst X.
Fan J. Haag
Monitoring of boundary currents
(CORC) with R. Davis P. Niiler
D. Roemmich B. Cornuelle D. Rudnick J.
Haag
The global timeseries system (OceanSITES)
with R. Weller and the
OceanSITES Teams
Uwe Send Scripps Institution of Oceanography
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• MOVE (Meridional Overturning
  Variability Experiment)
• Cost-effective concept to
• monitor transport of
• southward NADW between
• western boundary and
• Mid-Atlantic Ridge
• Assumptions
• Balances northwardthermocline transport(mass
  balance)
• Little transport east of MAR(reasonable based
  onCFC and model data,since 2006 full-basin
  coverage with German mooring in east)

Southward limb of MOC
MOVE array
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Initial array design (with added moorings from
M.McCartney GAGE) Integrate NADW flow over
1000km with geostrophic end-point moorings
NADW
Geostrophic Moorings

• Started in 2000 as German CLIVAR project, now
  fully NOAA funded.
• have demonstrated the accuracy
• learned how to achieve same with sparse array (2
  moorings epsilon)
• 8 ½ years of data now, 97 data return on
  internal and boundary transport

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NADW geostrophic transport rel. 4950db, and slope
transport from current meters
(large variability due to Rossby waves)
Absolute internal plus boundary transport (mean
-14.9Sv)
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The timeseries is about to become long enough now
to establish a trend
40 degrees of freedom, suggested transport
decrease 3Sv/10years (very similar to Bryden et
al 2005) The transport timeseries has a
significant decreasing trend with 80 certainty.
(Still need to test bias due to choice of
reference level and due to lacking eastern basin
component)
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• Lessons
• Have a large knowledge base now how to make such
  measurements accurately and efficiently
• Barotropic (reference pressure) transports
  currently have trend removed, nowstaggered/overla
  pping 4-year pressure timeseries are being
  collected
• Array now extended across entire Atlantic,
  expected to reduce Rossby-wavenoise ? more
  reliable transport estimates

• Outlook
• the timeseries will allow to establish an MOC
  trend at 16N within a few years
• merging observations from several latitudes (MOVE
  and RAPID) mayallow to isolate local vs.
  large-scale changes
• lessons/experience for MOC and boundary current
  monitoring at other places

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Boundary Current
monitoring Most of these current systems are
not covered at present...
CORC project develop and test methodologies for
sustained and real-time boundary current
observations (2 years completed now)
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• Existing SINGLE approaches fail in boundary
  currents
• ARGO and surface drifter density is too sparse
  in narrow and swift currents
• XBTs do not reach deep enough, miss salinity
  contribution, and sometimes are too manpower
  intensive (e.g. Gulf Stream), may alias transport
• end point moorings (as in MOVE) may capture mass
  transport but cannot resolve heat transport,
  are expensive and require annual turn if surface
  moored, miss non-geostrophic parts
• gliders are too slow (see Kessler presentation),
  not deep enough
• CORC objective
• Find optimal integration of above techniques to
  exploit their respective strengths

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CORC components currently being
implemented/tested
1) End-point moorings with bottom pressure High
temporal resolution of horizontal integral
(geostrophic MASS transport), full depth
2) Underwater gliders High horizontal resolution
of 0-1500m heat and average flow, every 1-2
weeks
3) Inverted echosounders plus bottom
pressure Limited horizontal sampling of 2
vertical integrals with good time resolution
? ? dz/c(z)
pbot g ? ?(z) dz
4) Data telemetry / near-real time products
Gliders as data relay for subsurface
instruments....
5) Additional elements - Surface drifters for
non-geostrophic flow, merging with ARGO and XBT
data - Assimilation of integrated data sets
together with altimetry and wind forcing
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Example sketch for Gulf Stream

• Moorings
• determine net mass transport, including eddies,
  recirculations,...
• For heat transport need
• vT dx dz
• Gliders
• provide regular upper layer T-weighting of v
  distribution in stream coordinates
• IESpressure
• when upper-layer flow and heat content is know,
  this provides lower-layer correlation of v and T.

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Possible, cost-effective configuration
Example total 4 gliders, 2 at the end points, 2
on a 500km section ? 1 trip each 2 weeks
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Initial implementation across the California
Current (later in Solomon Sea, see Kessler
presentation)

• Current status
• test mooring and IES near San Diego
• 1 glider with modem incorporated
• 2 short test glider missions
• downloaded 1 year of daily IES data
• 2 more gliders under construction
• auto-release drifters under construction
• 2 end point moorings, 5 IES to be deployed
  across California Current in Sep08 (trial phase)
• full deployment (less sparse) Sep09

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CORC Summary develop a capacity and start to
routinely observe
climate signatures in boundary currents

• Technology developments
• mooring and IES communication with gliders
• autonomous glider underwater acoustic navigation
• programmed releases of parked surface drifters
• tests of 2000m XBTs

• Methodological
• merge and exploit strengths of individual
  observing techniques
• connect to interior observing system
• test consistency/redundancy/accuracy of single
  elements
• assimilation of in-situ data, altimetry, winds,
  large-scale data to refine relevant quantities

• Climate applications
• interannual and decadal changes in the
  California Current
• relate circulation changes to climate phenomena
• impact on ecosystem and mechanisms (advection,
  propagation, local forcing)
• monitor source of EUC for variability in heat
  transport

• Sustained operation
• develop cost-effective procedures and operating
  facilities
• routine production of indices for circulation
  system

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a global network of FIXED open-ocean sites,
which

• collect timeseries of atmospheric, physical,
  biogeochemical, or ecosystem variables
• are sustained or planned to be sustained
• use mooring or ship-board (min. monthly) or
  cable or glider observations
• share data freely and in real-time/with minimum
  delay
• want to cooperate to be part of the network

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Recent OceanSITES developments and current
activities

• A) Assure data are useful and used by providing
  easy access
• 2 GDACs now exist and cooperate
  Coriolis/France and NDBC/USA
• national/regional DACs have been defined and
  their roles agreed
• a unified data format (NetCDF) is under
  revision and test
• data from 12 timeseries site operators will
  flow routinely within 12 months, from ONE
  place in ONE format
• 2 working groups established to agree on
  unified QC and best practices

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• B) Develop/provide products to a variety of users
  via www.oceanSITES.org, e.g.
• air-sea flux data from all flux sites for
  model validation
• 15m currents for validation of drifter and
  satellite current products
• sea surface salinities for remote sensing
  validation
• wave data measured by surface moorings for
  wave products/validation
• column integrated chlorophyll estimates for
  remote sensing/model validation
• more.

• C) Provide global ocean timeseries indicators on
  www.oceanSITES.org, e.g.
• pCO2 and pH from all the sites in the network
  measuring this
• boundary current transports
• assembled heat and freshwater content
  timeseries
• eddy energy timeseries where available
• geostrophic transports between pairs measuring
  dynamic height
• work towards ocean acidification and
  ecosystem indices

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• D) Make sites more similar and measurements more
  comparable
• Minimum set of sensors to have global impact for
  all disciplines
• met sensors
• Surface T/S and thermistors for mixed-layer depth
  resolution
• 0-1500m T/S sensors for dynamic height ?
  transport estimates
• Near-surface currents, minimum one at 15m
• Surface pCO2 for flux calculations
• Dissolved O2 at 5 depths for productivity and gas
  exchange estimates (with PCO2)
• Nitrate at 2 depths for mechanisms of
  forcing/limitation
• Downwelling radiometer at 20-30m and at surface
  for total biomass estimates

Choose 10-20 sites that can be enhanced by adding
some/all above sensors
Typical cost 200k per site
need about 2Mio to make
(initial) quantum leap
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Strawman set of sites that have the potential to
become a truly integrated core timeseries system
USA Europe Japan
Australia India OceanSITES
DART
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Activities in the future facilitated by 1)
Re-invigorated Steering and Data Management
Committees 2) Project Office support (started
and 50 funded by NOAA) at JCOMMOPS 3)
OceanSITES now is an official component of the
global ocean observing system, part of
JCOMM, and a pilot project of the Data Buoy
Coordination Panel (DBCP).
www.oceanSITES.org