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Geophysical Fluid Dynamics Laboratory Review June 30 - July 2, 2009 Atlantic Meridional Overturning Circulation and Climate Presented by Rong Zhang Introduction Atlantic Meridional Overturning Circulation (AMOC) Global Scale Impact in Paleo Climate

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Presentation Transcript
slide3

Introduction

Atlantic Meridional Overturning Circulation (AMOC)

  • Global Scale Impact in Paleo Climate
  • Global Scale Impact in Modern Climate
  • AMOC Fingerprints
slide4

Modeled responses due to the weakening of AMOC

Precipitation (shading) and SLP

Drying

Precipitation (shading) and Surface Wind

Drying

Global Synchronization of Abrupt Climate Change in Response to AMOC Collapse

Schematic diagram of global synchronization of abrupt climate change indicated bypaleo records

  • A substantial weakening of the AMOC is linked to:
  • Southward shift of ITCZ in Atlantic and Pacific
  • Weaker East Asia and Indian Summer Monsoons

(Zhang and Delworth 2005)

slide5

Regression of Summer Rainfall on AMO Index

Wetting

OBS

MODEL

Regression of vertical shear on AMO index

OBS

MODEL

Reduction

Atmospheric Impact of Atlantic Multidecadal Oscillation (AMO)

  • The AMO (area averaged detrended SST anomalies over the North Atlantic) can lead to:
  • Multidecadal variations in Sahel and India summer rainfall, and vertical shear over the Atlantic Hurricane MDR (Zhang and Delworth 2006)
  • Northern Hemispheric mean surface temperature fluctuations (Zhang et al. 2007)
  • Multidecadal variations in the Northern Pacific (Zhang and Delworth 2007)
slide6

Warming

Cooling

Ocean temperature anomaly due to the weakening of AMOC

MODEL

MODEL

Cooling

Warming

Surface

Subsurface (z=400m)

Tropical Fingerprint of AMOC Variability

The link between AMO and AMOC is highly debated. Developing AMOC fingerprints is crucial for understanding the origin and the attribution of observed SST variations.

Observed Tropical North Atlantic (TNA) SST is anticorrelated with TNA subsurface ocean temperature. The anticorrelation is a fingerprint of AMOC variations in coupled model simulations, indicating observed TNA SST fluctuations may be AMOC-related (Zhang 2007).

slide7

Observed SSH PC1 and subsurface temperature (Tsub) PC1

Observed SSH PC1

r(SSH,Tsub) = 0.98

Modeled SSH PC1, Tsub PC1, AMOC Index

r(SSH,Tsub) = 0.85

Extra-tropical Fingerprint of AMOC Variability

The leading modes of SSH and subsurface temperature constitute a fingerprint of AMOC variations, and might be used as AMOC proxies. It indicates that during the 60’s and the recent decade, the AMOC was stronger, and the recent slowdown of the subpolar gyre is a multidecadal variation (Zhang 2008).

summary
Simulated global synchronization of abrupt climate change due to the AMOC collapse is consistent with that indicated by paleo records.

The AMO can lead to multidecadal variations in Sahel and India summer rainfall, Atlantic Hurricane activity, northern hemispheric surface temperature, and Northern Pacific SST.

AMOC fingerprints are developed and could be used for AMOC reconstruction in the past. They suggest that the observed AMO is linked to AMOC variations.

Observations of SSH and subsurface temperature could be used to monitor AMOC variations.

Summary