North Atlantic Simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II): Inter-Annual to Decadal Variability
North Atlantic Simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II): Inter-Annual to Decadal Variability
Abstract:
Simulated inter-annual to decadal variability and trends in the North Atlantic for the
1958-2007 period from twenty global ocean - sea-ice coupled models are presented.
These simulations are performed as contributions to the second phase of the Coordinated
Ocean-ice Reference Experiments (CORE-II). A major focus of the present study is the representation of Atlantic
meridional overturning circulation (AMOC) variability in the participating models.
Relationships between AMOC variability and those of some other related variables, such
as subpolar mixed layer depths, the North Atlantic Oscillation (NAO), and the Labrador
Sea upper-ocean hydrographic properties, are also investigated. In general, AMOC
variability shows three distinct stages. During the first stage that lasts until the mid-
to late-1970s, AMOC is relatively steady, remaining lower than its long-term
(1958-2007) mean. Thereafter, AMOC intensifies with maximum transports achieved in the mid- to late-1990s. This enhancement is
then followed by a weakening trend until the end of our integration period. This
sequence of low frequency AMOC variability is consistent with previous studies.
Regarding strengthening of AMOC between about the mid-1970s and the mid-1990s, our results
support a previously identified variability mechanism where AMOC intensification is
connected to increased deep water formation in the subpolar North Atlantic, driven
by NAO-related surface fluxes. The simulations tend to show general agreement in their
representations of, for example, AMOC, sea surface temperature (SST), and subpolar mixed layer
depth variabilities. In particular, the observed variability of the North Atlantic SSTs is
captured well by all models. These findings indicate that simulated variability and
trends are primarily dictated by the atmospheric datasets which include the influence
of ocean dynamics from nature superimposed onto anthropogenic effects. Despite these
general agreements, there are many differences among the model solutions, particularly in the spatial structures of variability
patterns. For example, the location of the maximum AMOC variability differs among the
models between Northern and Southern Hemispheres.
1958-2007 period from twenty global ocean - sea-ice coupled models are presented.
These simulations are performed as contributions to the second phase of the Coordinated
Ocean-ice Reference Experiments (CORE-II). A major focus of the present study is the representation of Atlantic
meridional overturning circulation (AMOC) variability in the participating models.
Relationships between AMOC variability and those of some other related variables, such
as subpolar mixed layer depths, the North Atlantic Oscillation (NAO), and the Labrador
Sea upper-ocean hydrographic properties, are also investigated. In general, AMOC
variability shows three distinct stages. During the first stage that lasts until the mid-
to late-1970s, AMOC is relatively steady, remaining lower than its long-term
(1958-2007) mean. Thereafter, AMOC intensifies with maximum transports achieved in the mid- to late-1990s. This enhancement is
then followed by a weakening trend until the end of our integration period. This
sequence of low frequency AMOC variability is consistent with previous studies.
Regarding strengthening of AMOC between about the mid-1970s and the mid-1990s, our results
support a previously identified variability mechanism where AMOC intensification is
connected to increased deep water formation in the subpolar North Atlantic, driven
by NAO-related surface fluxes. The simulations tend to show general agreement in their
representations of, for example, AMOC, sea surface temperature (SST), and subpolar mixed layer
depth variabilities. In particular, the observed variability of the North Atlantic SSTs is
captured well by all models. These findings indicate that simulated variability and
trends are primarily dictated by the atmospheric datasets which include the influence
of ocean dynamics from nature superimposed onto anthropogenic effects. Despite these
general agreements, there are many differences among the model solutions, particularly in the spatial structures of variability
patterns. For example, the location of the maximum AMOC variability differs among the
models between Northern and Southern Hemispheres.