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Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science.

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Presentation on theme: "Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science."— Presentation transcript:

1 Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science Christopher D. Roberts 3, Eleanor Frajka-Williams 2, William E. Johns 4, Will Hobbs 5, Matthew D. Palmer 3, Darren Rayner 1, David A. Smeed 1, Gerard McCarthy 1 1 National Oceanography Centre Southampton, 2 University of Southampton, 3 Met Office, Exeter, 4 RSMAS, University of Miami, 5 IMAS, Hobart.

2 OHC error ~=0.2x10 22 J A cold subtropical North Atlantic

3 Spatial and Temporal Pattern of Ocean Heat Content in the North Atlantic ( seasonal cycle removed & 0 to 2000 m) Enhanced Ocean Data Assimilation and Climate Prediction EN3 v2a gridded objective analysis of quality-controlled sub-surface temperature observations (Ingleby and Huddleston 2007,

4 OHC (10 22 J) : Feb 2004

5 OHC (10 22 J) : Aug 2004

6 OHC (10 22 J) : April 2005

7 OHC (10 22 J) : Aug 2005

8 OHC (10 22 J) : Sept 2006

9 OHC (10 22 J) : May 2007

10 OHC (10 22 J) : Oct 2009

11 OHC (10 22 J) : March 2010

12 OHC (10 22 J) : Jan 2011

13 OHC (10 22 J) : Sept 2011

14 Observing the AMOC and Associated Heat Flux 41°N Johns, W. E., et al., (2011). "Continuous, array-based estimates of Atlantic Ocean heat transport at 26.5°N." J. Clim. 24(10): Hobbs, W. R. and J. K. Willis (2012). "Midlatitude North Atlantic heat transport: A time series based on satellite and drifter data." J. Geophys. Res. 117(C01008): doi: /2011JC

15 Subtropical Atlantic Heat Budget (0-2000m) S’ 26.5°N N’ 41.0°N F’ surface flux 0 m 2000 m

16 Meridional Heat Transport and Divergence 1/4/04 to 31/3/09MeanSD 26.5°N °N °N /4/08 to 31/3/10MeanSD 26.5°N °N °N

17 Ocean Heat Content

18 ERA-Interim surface flux anomalies

19 Relative Heat Content Change Palmer & Haines (2009): Estimating oceanic heat content change using isotherms, J.Clim, 22,

20 What generates the MLD (  >14°C) temperature anomalies?

21 Summary 1.Sustained cooling in upper 2 km of subtropical Atlantic between OHC change partitioned equally between the seasonal mixed layer >14°C and deep ocean. 3.Reduced AMOC at 26.5°N is the largest contributor to reduced MHT divergence. 4.In seasonal mixed layer heat loss is due to atmospheric heat loss (60%) and MHT divergence (40%). 5.Results emphasise the role for the ocean in the North Atlantic climate system on seasonal to interannual timescales and suggest a role for the AMOC in setting sub- surface temperature anomalies. 6.These anomalies have previously been linked to re-emerging SST patterns and subsequent NAO anomalies.

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23 Need to do a bit about re-emergence/SST patterns and link to NAO (Taws). Then say we identify the OHC change due to divergence as responsible.

24 OHC Errors

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26 Ekman and Geostrophic Heat Transport Variability

27 Interannual Variability What happened to the MOC in ? Table of annual changes (Std of annual means): Layer (change) Mean [Sv]Std [Sv]Mean [Sv] MOC (-5.9) Gulf Stream (-1.1) Ekman (-1.8) Upper mid-ocean (-3.2) UNADW ( m) (1.2) LNADW ( m) (4.0)

28 RAPID MOC: , Ekman constant What happened to the MOC in , not directly due to Ekman? Table of annual changes (Ekman fixed): Layer (change) Mean [Sv]Std [Sv]Mean [Sv] MOC (-4.4) Gulf Stream (-1.1) Ekman (0) Upper mid-ocean (+3.2) UNADW ( m) (-0.7) LNADW ( m) (-3.3) Longer duration (18-month) slowdown of the MOC: seen in the Gulf Stream, upper mid-ocean and LNADW.

29 MOC timeseries and related data products are available from Data from individual instruments are available from Gulf Stream, MOC, Ekman & Upper Mid-Ocean Transports (10-day & 3-month, low-pass filtered) Gulf Stream MOC Ekman Upper Mid-Ocean LNADW (3-5km) UNADW (1.1-3km)

30 Meridional Heat Transport Time Series Johns, et al. (2011), Continuous array-based estimates of Atlantic Ocean Heat Transport at 26.5N, JClim

31 Meridional Heat Transport at 26.5°N Contribution to Q net by spatially correlated v,T variability across interior from argo data.. Q GS → Cable voltage calibrated for temperature transport, (Shoosmith et al., 2005) r = 0.94, σ = 0.1 PW Q Ek → ECMWF ERA Interim wind stress (daily) Reynolds SST (weekly) Q WBW → Directly calculated from moored CM’s/thermistors in Abaco WB array Q INT → Zonally-averaged interior transport profile from endpoint geostrophic moorings Seasonally-varying interior hyrdographic climatology (Hydrobase, R. Curry) merged with argo data.

32 Ocean Heat Content

33 26.5°N 1.26±0.11 PW Hobbs & 41°N 0.48±0.11 PW TF08 error bars Coupled models (CM2.1, CCSM4) Radiation balance residual (NCEP,ECMWF,TF08)l Global hydro inverse (Ganachaud) Air-sea flux climatology (Large) RAPID & 41N: Direct Residual Radiation Balance, Climatologies and Direct Estimates Atlantic Ocean Heat Transport Estimates

34 Overturning and Gyre Heat Transport

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38 Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science, Oban Christopher D. Roberts 3, Eleanor Frajka-Williams 2, William E. Johns 4, Will Hobbs 5, Matthew D. Palmer 3, Darren Rayner 1, David A. Smeed 1, Gerard McCarthy 1 1 National Oceanography Centre Southampton, 2 University of Southampton, 3 Met Office, Exeter, 4 RSMAS, University of Miami, 5 IMAS, Hobart.


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