Comparison of the Stability of the Atlantic Thermohaline Circulation in Two Coupled Atmosphere–Ocean General Circulation Models

2007 ◽  
Vol 20 (17) ◽  
pp. 4293-4315 ◽  
Author(s):  
Jianjun Yin ◽  
Ronald J. Stouffer
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Large Scale ◽  
Thermohaline Circulation ◽  
General Circulation Models ◽  
Ocean General Circulation Models ◽  
Intercomparison Project ◽  
Ocean General Circulation ◽  
Atlantic Thermohaline Circulation ◽  
Atmospheric Feedback

Abstract Two coupled atmosphere–ocean general circulation models developed at GFDL show differing stability properties of the Atlantic thermohaline circulation (THC) in the Coupled Model Intercomparison Project/Paleoclimate Modeling Intercomparison Project (CMIP/PMIP) coordinated “water-hosing” experiment. In contrast to the R30 model in which the “off” state of the THC is stable, it is unstable in the CM2.1. This discrepancy has also been found among other climate models. Here a comprehensive analysis is performed to investigate the causes for the differing behaviors of the THC. In agreement with previous work, it is found that the different stability of the THC is closely related to the simulation of a reversed thermohaline circulation (RTHC) and the atmospheric feedback. After the shutdown of the THC, the RTHC is well developed and stable in R30. It transports freshwater into the subtropical North Atlantic, preventing the recovery of the salinity and stabilizing the off mode of the THC. The flux adjustment is a large term in the water budget of the Atlantic Ocean. In contrast, the RTHC is weak and unstable in CM2.1. The atmospheric feedback associated with the southward shift of the Atlantic ITCZ is much more significant. The oceanic freshwater convergence into the subtropical North Atlantic cannot completely compensate for the evaporation, leading to the recovery of the THC in CM2.1. The rapid salinity recovery in the subtropical North Atlantic excites large-scale baroclinic eddies, which propagate northward into the Nordic seas and Irminger Sea. As the large-scale eddies reach the high latitudes of the North Atlantic, the oceanic deep convection restarts. The differences in the southward propagation of the salinity and temperature anomalies from the hosing perturbation region in R30 and CM2.1, and associated different development of a reversed meridional density gradient in the upper South Atlantic, are the cause of the differences in the behavior of the RTHC. The present study sheds light on important physical and dynamical processes in simulating the dynamical behavior of the THC.

scholarly journals On the use of Schwarz–Christoffel conformal mappings to the grid generation for global ocean models

2015 ◽  
Vol 8 (10) ◽  
pp. 3471-3485 ◽  
Author(s):  
S. Xu ◽  
B. Wang ◽  
J. Liu
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Grid Cell ◽  
Grid Generation ◽  
General Circulation Models ◽  
Conformal Mappings ◽  
Ocean Modeling ◽  
Global Ocean ◽  
Ocean General Circulation Models ◽  
Ocean General Circulation

Abstract. In this article we propose two grid generation methods for global ocean general circulation models. Contrary to conventional dipolar or tripolar grids, the proposed methods are based on Schwarz–Christoffel conformal mappings that map areas with user-prescribed, irregular boundaries to those with regular boundaries (i.e., disks, slits, etc.). The first method aims at improving existing dipolar grids. Compared with existing grids, the sample grid achieves a better trade-off between the enlargement of the latitudinal–longitudinal portion and the overall smooth grid cell size transition. The second method addresses more modern and advanced grid design requirements arising from high-resolution and multi-scale ocean modeling. The generated grids could potentially achieve the alignment of grid lines to the large-scale coastlines, enhanced spatial resolution in coastal regions, and easier computational load balance. Since the grids are orthogonal curvilinear, they can be easily utilized by the majority of ocean general circulation models that are based on finite difference and require grid orthogonality. The proposed grid generation algorithms can also be applied to the grid generation for regional ocean modeling where complex land–sea distribution is present.

scholarly journals Investigating the Causes of the Response of the Thermohaline Circulation to Past and Future Climate Changes

2006 ◽  
Vol 19 (8) ◽  
pp. 1365-1387 ◽  
Author(s):  
R. J. Stouffer ◽  
J. Yin ◽  
J. M. Gregory ◽  
K. W. Dixon ◽  
M. J. Spelman ◽  
...  
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Climate Changes ◽  
Thermohaline Circulation ◽  
General Circulation Models ◽  
Freshwater Input ◽  
Multimodel Ensemble ◽  
Critical System ◽  
Intercomparison Project ◽  
Atlantic Itcz

Abstract The Atlantic thermohaline circulation (THC) is an important part of the earth's climate system. Previous research has shown large uncertainties in simulating future changes in this critical system. The simulated THC response to idealized freshwater perturbations and the associated climate changes have been intercompared as an activity of World Climate Research Program (WCRP) Coupled Model Intercomparison Project/Paleo-Modeling Intercomparison Project (CMIP/PMIP) committees. This intercomparison among models ranging from the earth system models of intermediate complexity (EMICs) to the fully coupled atmosphere–ocean general circulation models (AOGCMs) seeks to document and improve understanding of the causes of the wide variations in the modeled THC response. The robustness of particular simulation features has been evaluated across the model results. In response to 0.1-Sv (1 Sv ≡ 106 m3 s−1) freshwater input in the northern North Atlantic, the multimodel ensemble mean THC weakens by 30% after 100 yr. All models simulate some weakening of the THC, but no model simulates a complete shutdown of the THC. The multimodel ensemble indicates that the surface air temperature could present a complex anomaly pattern with cooling south of Greenland and warming over the Barents and Nordic Seas. The Atlantic ITCZ tends to shift southward. In response to 1.0-Sv freshwater input, the THC switches off rapidly in all model simulations. A large cooling occurs over the North Atlantic. The annual mean Atlantic ITCZ moves into the Southern Hemisphere. Models disagree in terms of the reversibility of the THC after its shutdown. In general, the EMICs and AOGCMs obtain similar THC responses and climate changes with more pronounced and sharper patterns in the AOGCMs.

scholarly journals Sea-air CO2fluxes and carbon transport: A comparison of three ocean general circulation models

2000 ◽  
Vol 14 (4) ◽  
pp. 1267-1281 ◽  
Author(s):  
J. L. Sarmiento ◽  
P. Monfray ◽  
E. Maier-Reimer ◽  
O. Aumont ◽  
R. J. Murnane ◽  
...  
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Ocean General Circulation Models ◽  
Ocean General Circulation ◽  
Carbon Transport

A Series of Zonal Jets Embedded in the Broad Zonal Flows in the Pacific Obtained in Eddy-Permitting Ocean General Circulation Models

2005 ◽  
Vol 35 (4) ◽  
pp. 474-488 ◽  
Author(s):  
Hideyuki Nakano ◽  
Hiroyasu Hasumi
Keyword(s):  
General Circulation ◽  
Bottom Topography ◽  
Zonal Flow ◽  
General Circulation Models ◽  
Wind Forcing ◽  
Zonal Flows ◽  
Zonal Jets ◽  
The Pacific ◽  
Ocean General Circulation Models ◽  
Ocean General Circulation

Abstract A series of zonal currents in the Pacific Ocean is investigated using eddy-permitting ocean general circulation models. The zonal currents in the subsurface are classified into two parts: one is a series of broad zonal flows that has the meridional pattern slanting poleward with increasing depth and the other is finescale zonal jets with the meridional scale of 3°–5° formed in each broad zonal flow. The basic pattern for the broad zonal flows is similar between the coarse-resolution model and the eddy-permitting model and is thought to be the response to the wind forcing. A part of the zonal jets embedded in each zonal flow is explained by the anomalous local wind forcing. Most of them, however, seem to be mainly created by the rectification of turbulent processes on a β plane (the Rhines effect), and zonal jets in this study have common features with the zonally elongated flows obtained in previous modeling studies conducted in idealized basins. The position of zonal jets is not stable when the ocean floor is flat, whereas it oscillates only within a few degrees under realistic bottom topography.

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