Presentation on theme: "Atlantic Meridional Overturning Circulation Slowdown Causes Widespread Cooling In The Atlantic Stuart A. Cunningham Scottish Association for Marine Science."— Presentation transcript:
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.
OHC error ~=0.2x10 22 J A cold subtropical North Atlantic
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,
OHC (10 22 J) : Feb 2004
OHC (10 22 J) : Aug 2004
OHC (10 22 J) : April 2005
OHC (10 22 J) : Aug 2005
OHC (10 22 J) : Sept 2006
OHC (10 22 J) : May 2007
OHC (10 22 J) : Oct 2009
OHC (10 22 J) : March 2010
OHC (10 22 J) : Jan 2011
OHC (10 22 J) : Sept 2011
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
Subtropical Atlantic Heat Budget (0-2000m) S’ 26.5°N N’ 41.0°N F’ surface flux 0 m 2000 m
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
What generates the MLD ( >14°C) temperature anomalies?
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.
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.
Ekman and Geostrophic Heat Transport Variability
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)
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.
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)
Meridional Heat Transport Time Series Johns, et al. (2011), Continuous array-based estimates of Atlantic Ocean Heat Transport at 26.5N, JClim
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.
Ocean Heat Content
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
Overturning and Gyre Heat Transport
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.