Key role of internal thermohaline ocean dynamics in Atlantic Multidecadal Variability: multiple lines of evidence from both observations and simulations
Abstract
This study presents multiple lines of evidence from observations and model simulations that support a key role for ocean thermohaline dynamics, rather than external forcings, in Atlantic multidecadal variability (AMV). Observed AMV fingerprints considered here include the low-frequency spatiotemporal evolution of sea surface temperature, surface heat fluxes, and deep ocean hydrography. While largely absent in the forced response of the Community Earth System Model (CESM) Large Ensemble (LENS) historical simulations, these fingerprints are clearly discernible in the regression analysis using the long control simulation of LENS where the variability is purely internal, and in the perturbed ensemble experiments where surface heat flux anomalies are imposed only in the Labrador Sea in order to perturb deep water formation there and, thereby, thermohaline circulation only. Further evidence derives from initialized decadal prediction simulations (CESM Decadal Prediction Large Ensemble), which exhibit much higher skill at predicting the observed AMV of the past 50 years than LENS. The high correlation between the observed AMV and the externally-forced version derived from LENS, which has been invoked as evidence for externally driven AMV, is shown to be largely an artifact of concurrent warming since the 1990s.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A23S3037K
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 4504 Air/sea interactions;
- OCEANOGRAPHY: PHYSICAL