rapid-watch/mocha atlantic meridional overturning circulation and heat flux monitoring array at...
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RAPID-WATCH/MOCHAAtlantic Meridional Overturning Circulation and
Heat Flux Monitoring Array at 26.5°N
Chris Atkinson, Molly Baringer, Lisa Beal, Harry Bryden, Maria-Paz Chidichimo, Julie Collins, Stuart Cunningham, Aurélie
Duchez, Joel Hirschi, William Johns, Helen Johnson, Torsten Kanzow, Jochem Marotzke, David Marshall, Gerard McCarthy, Chris Meinen, Aazani Mujahid, Darren Rayner,
Zoltan Szuts, Eleanor Frajka-Williams
Gerard McCarthy and
Stuart Cunningham
National Oceanography Centre
Outline
1. How do we estimate the MOC at 26.5°N?
2. Basinwide transports in an Eddy-filled Ocean
3. Seasonal Variability at 26.5°N
4. Atlantic Ocean Heat Transport at 26.5°N
5. Recent Changes in the MOC at 26.5°N
How do we estimate the MOC at 26.5°N?
Western Boundary Wedge Currents and the mid-ocean Dynamic Height and Bottom Pressure Array
Rayner, D., et al. (2011), Monitoring the Atlantic Meridional Overturning Circulation, Deep Sea Research II, in press.
Johns, W. E., L. M. Beal, M. O. Baringer, J. Molina, D. Rayner, S. A. Cunningham, and T. O. Kanzow (2008), Variability of shallow and deep western boundary currents off the Bahamas during 2004-2005: First results from the 26°N RAPID-MOC array, J. Phys. Oceanog., 38(3), 605-623.
Overturning stream function
red dots
Zero Nett Mass transport as observed e.g. Bryden, H. L., et al.(2009) Ocean Science, 6, 871-908.
Ekman transports from ECMWF ERA-Interim winds since demise of QuickScat
Gulf Stream transports from Florida Straits Cable measurements
Mean [Sv]
GS
31.8±3.1
MOC
18.1±4.3
Ekman
2.9±3.0
UMO
-16.6±3.4
• MOC timeseries and related data products are available from www.noc.soton.ac.uk/rpdmoc• Data from individual instruments are available from www.bodc.ac.uk
Gulf Stream, MOC, Ekman & Upper Mid-Ocean Transports (10-day & 3-month, low-pass filtered)
April 2004 to April 2009
Mean [Sv]
GS
31.6±3.1
MOC
17.2±4.9
Ekman
2.6±3.3
UMO
-16.9±3.5
Gulf Stream, MOC, Ekman & Upper Mid-Ocean Transports (10-day & 3-month, low-pass filtered)
April 2004 to Dec 22nd 2010
• MOC timeseries and related data products are available from www.noc.soton.ac.uk/rpdmoc• Data from individual instruments are available from www.bodc.ac.uk
Basinwide Transports in an Eddy-filled Ocean
RMS amplitude of SSH and dynamic height along 26.5°N
See also:Bryden, H. L., A. Mujahid, S. A. Cunningham, and T. Kanzow (2009), Adjustment of the basin-scale circulation at 26°N to variations in Gulf Stream, deep western boundary current and Ekman transports as observed by the Rapid array, Ocean Science, 6, 871-908.0 (km)
1000
Kanzow, T., H. Johnson, D. Marshall, S. A. Cunningham, J. J.-M. Hirschi, A. Mujahid, H. L. Bryden, and W. E. Johns (2009), Basin-wide integrated volume transports in an eddy-filled ocean, J. Phys. Oceanog., 39(12), 3091–3110.
• The eddy field at 26.5°N does not dominate MOC variability on
interannual to decadal timescales, and does not pose as large a
signal-to-noise problem for detection of secular trends.
• SSH fluctuations increase from east to west, but decrease sharply
within 100 km from Abaco shelf, in agreement with upper ocean
transports.
Basin wide transports in an eddy-filled oceanConclusions
Seasonal Variability at 26.5°N
±1.8 Sv,SE=1.0 Sv
±2.6 Sv, SE=0.5 Sv
SD 3.5 Sv, Range 7.0 Sv
SD 3.1 Sv, Range 6.2 Sv
Contribution of the upper mid-ocean western and eastern boundaries to the UMO seasonal cycle
Kanzow, T., et al. (2010), Seasonal variability of the Atlantic meridional overturning circulation at 26.5°N, J. Clim., 23(21), doi: 10.1175/2010JCLI3389.1171.
Chidichimo, M. P., T. Kanzow, S. A. Cunningham, W. E. Johns, and J. Marotzke (2010), The contribution of eastern-boundary density variations to the Atlantic meridional overturning circulation at 26.5 N, Ocean Science, 6,
Atkinson, C. P., H. L. Bryden, J. J.-M. Hirschi, and T. Kanzow (2010), On the seasonal cycles and variability of Florida Straits, Ekman and Sverdrup transports at 26° N in the Atlantic Ocean, Ocean Science, 6(4), 10.5194/os-5196-5837-2010.
Seasonal variabilityConclusions
• MOC seasonal cycle is 6.7 Sv peak-to-peak.
• UMO contributes the most pronounced seasonal
cycle of 5.9 Sv.
• Seasonal cycle in UMO is caused by vertical density
fluctuations at the Eastern Boundary forced by
seasonal anomalies in the wind stress curl.
Atlantic Ocean Heat Transport at 26.5°N
Meridional Heat/Temperature Transport Variability
Contribution to the net heat transport variance (relative to the mid-ocean temperature)
FC=20%
EK=46%WBW=8%Gyre/eddy=1%
Mid-ocean=25%
Mer
idiona
l Hea
t Tra
nspo
rt (P
W)
Tem
pera
ture
tran
spor
t (re
lativ
e to
0°C
)Net Heat Flux = 1.27 ± 0.30 PW (uncertainty 0.14 PW)
Johns, W. et al. (2011), Continuous, Array-based Estimates of Atlantic Heat Transport at 26.5°N, J. Clim., 24, pp. 2429–2449.
Meridional Heat TransportConclusions
•The mean MHT (2004 to 2007) is 1.27 ± 0.3 PW.
•Ekman contributes 46% of heat flux variability; Mid-ocean geostrophic fluctuations 25%.
•Seasonal cycle 0.9 PW, dominated by the mid-ocean geostrophic variability. Maximum in summer/fall and minimum in March.
•MHT is highly correlated with changes in strength of the MOC. The overturning accounts for 90% of the total MHT.
Recent Changes in the MOC at 26.5°N
Mean [Sv]
GS
31.6±3.1
MOC
17.2±4.9
Ekman
2.6±3.3
UMO
-16.9±3.5
Gulf Stream, MOC, Ekman & Upper Mid-Ocean Transports (10-day & 3-month, low-pass filtered)
April 2004 to Dec 22nd 2010
• MOC timeseries and related data products are available from www.noc.soton.ac.uk/rpdmoc• Data from individual instruments are available from www.bodc.ac.uk
Gulf Stream, MOC, Ekman & Upper Mid-Ocean Transports (10-day & 3-month, low-pass filtered)
April 2004 to Dec 22nd 2010
NAO Index
Extreme Lows in NAO, Winter 09/10 and 10/11
Jung, T. et al. (2011), Origin and predictability of the extreme negative NAO winter of 2009/10, Geophysical Res. Lett., 38, L07701.
Wang, C. et al. (2010), The record-breaking cold temperatures during the winter of 2009/2010 in the Northern Hemisphere, Atmoshperic Sci. Lett., 11, 161-168.
Component Transports and Layer Transports April 2004 to Dec 22nd 2010
Lower NADW (Blue line, Lower panel) declines in winter 2009/2010 at the same time as MOC and Ekman event (Red and Black lines, Upper panel)
Decline in the Lower NADW evident from historical hydrography (Bryden et al. [2005]) and it is a water mass expected to decline first with MOC decline (Doshcher et al. [1994])
CONCLUSIONS• The RAPID array is delivering twice daily estimates of the strength
and structure of the AMOC since 2004.
• AMOC mean is 17.2±4.9 Sv, but in the year of 2009/10 was only 12.0 Sv, and during the winter was southward on occasion due to extremely negative NAO.
• Variability due to eddies diminishes towards the boundaries where the RAPID measurements are made
• Seasonal variability in the AMOC is nearly 7 Sv. Wind stress curl at the eastern boundary drives the anomalies.
• Heat Flux is 1.35 PW, of which 90% is carried in the AMOC.