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Robust and Nonrobust Aspects of AMOC Variability and Mechanisms in CESM

Robust and nonrobust aspects of Atlantic meridional overturning circulation (AMOC) variability and mechanisms are analyzed in several 600-yr simulations with the Community Earth System Model. The simulations consist of a set of cases where a few loosely constrained ocean model parameter values are changed, a pair of cases where round-off level perturbations are applied to the initial atmospheric temperature field, and a millennium-scale integration. The time scales of variability differ among the cases with the dominant periods ranging from decadal to centennial. These dominant periods are not stationary in time, indicating that a robust characterization of AMOC temporal variability requires long, multimillennium-scale simulations. A robust aspect is that positive anomalies of the Labrador Sea (LS) upper-ocean density and boundary layer depth and the positive phase of the North Atlantic Oscillation lead AMOC strengthening by 2–3 years. Respective contributions of temperature and salinity to these density anomalies vary across the simulations, but in a majority of the cases temperature contributions dominate. Following an AMOC intensification, all cases show that advection of warm and salty waters into the LS region results in near-neutral density anomalies. Analysis of the LS heat budget indicates that temperature acts to increase density in all cases prior to an AMOC intensification, primarily due to losses by sensible and latent heat fluxes. The accompanying salt budget analysis reveals that the salt contribution to density anomalies varies across the cases, taking both positive and negative values.

This dataset contains an ensemble of fully coupled CESM1 sensitivity experiments where select ocean model parameter are changed within acceptable ranges to investigate their impact on AMOC. All simulations are 600 years long, and monthly means are available over the North Atlantic region (80W-60E ; 40N-75N).
Frederic Castruccio
Gokhan Danabasoglu
Laura Landrum
Stephen G. Yeager
Peter R. Gent

Related Activities
Project - CCSM

Child Datasets

Vertical background diffusivity is reduced from 0.17×10−4 to 0.10×10−4 m2s−1
Length scale (width) of the mixed layer fronts in the submesoscale mixing parameterization is reduced from 5 to 3.3 km
Minimum isopycnal and thickness diffusivity value in the deep / abyssal ocean is increased from 300 to 600 m2s−1
Interior horizontal viscosity is reduced from 600 to 300 m2s−1
Isopycnal and thickness diffusivity value in the surface boundary layer is reduced from 3000 to 2000 m2s−1
Round-off level perturbations are applied to the initial air temperature field
Round-off level perturbations are applied to the initial air temperature field
Date Created
2023-03-09 08:10:41
Date Last Updated
2023-03-13 10:46:10
Version Date Publisher Published State Source
1.0 2023-03-09 08:10:41 Teagan King Published
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