Atlantic Multidecadal Variability and Its Climate Impacts in CMIP3
Models and Observations
Mingfang TingWith
Yochanan Kushnir, Richard Seager, Cuihua Li
June 8, 20102010 U.S. AMOC Annual Meeting
Miami, FL
Observed AMO (AMV) Indices
North Atlantic SST Index (7.5W-75W, 0-60N, ocean only) for Models and Observations
Linear de-trending
Global mean SST as forced signal
Signal to noise EOF PC1 as forced signal (Ting et al, 2009)
Forced Atlantic SST in models
Observed AMV
Climate Impacts of Forced versus Internal NASST Variability (Regression based on Annual
Mean) InternalForced
T sPre
cip
.
(Stippled regions are for values significant at or above 95% confidence level)
What are the spatial and temporal characteristics and climate impacts of AMV in CMIP3 models for both the 20th and 21st Centuries?
Hoe do they compare to 20th Century observations?
Is the signal to noise maximizing EOF method successfully separating AMV from the externally forced component?
Questions to be Addressed:
In this study… Apply signal-to-Noise Maximizing EOF Analysis to
IPCC multiple model, multi-ensemble members of the 20th and 21st simulations
First apply EOF analysis to deviations from multi-model average to determine the spatial structure of the internal modes of variability (noise)
Apply a spatial pre-whitening transformation based on the internal EOFs to remove the spatial correlations in the internal atmospheric variability (i.e., “climate noise”) contained in the multi-model average
Apply EOF analysis to the signal to get forced component
S/N Maximizing EOF 1 for 19 IPCC Model Simulations
20th Century 21st Century
Obs.
Comparison of 20th and 21st Century AMV in CMIP3 Models
20th Century 21st Century
(Stippled regions indicate at least 15 out of 19 models have the same sign regression)
Forced Internal
Regression of Ts and Precip on Forced versus Internal NASST Variability (Annual Mean 20th Century)
Ts
Precip Precip
Ts
(Stippled regions indicate at least 15 out of 19 models have the same sign regression)
Forced Internal
Regression of Ts and Precip on Forced versus Internal NASST Variability (Annual Mean 21st Century)
Ts
Precip Precip
Ts
Ts Regression (Annual)Forced Internal (AMV)
Obs.
20th
21st
Obs.
20th
21st
Precip Regression (Annual)Forced Internal (AMV)
Obs.
20th
21st
Obs.
20th
21st
AMV in Pre-Industrial CMIP3 Runs Can we reproduce AMV spatial patterns
and climate impacts in a model without radiatively forced changes?
If so, what are the typical time scales and amplitude of the AMV?
What are the circulation features associated with the AMV?
AMV Amplitude
Pre-Industrial
20th Century
21st Century
AMV Surface Temperature Regression(Annual Mean)
Stippling indicates sign agreement for 15 out of the 20 models or 5% significance (obs.)
Pre-Industrial 21st Century
20th Century Observations
AMV Precipitation Regression(Annual Mean)
Stippling indicates sign agreement for 15 out of the 20 models or 5% significance (obs.)
Pre-Industrial 21st Century
20th Century Observations
AMV and AMOC
Atlantic Meridional Overturning Streamfunction
Summary A robust spatial pattern of AMV is identified for
observations, CMIP3 models’ pre-industrial, 20th and 21st Century simulations, despite the differing temporal scales between models and observations.
The AMV spatial pattern is characterized by a comma-shaped SST pattern over the North Atlantic with the largest amplitude in the sub-polar region which extends to the tropical Atlantic along the east side of the basin.
The precipitation patterns associated with AMV are remarkably similar for the pre-industrial and 20th Century model simulations, and to some extent for the 21st Century simulations and observations. The positive phase of AMV (warm North Atlantic) is associated with northward shifted Atlantic ITCZ, increased rainfall over Sahel and eastern tropical Pacific, and dry condition over tropical south Atlantic, North America and Australia.
Top Related