Spectral Characteristics of the Response of the Meridional Overturning Circulation to Deep-Water Formation

Deshayes, Julie; Frankignoul, Claude

doi:10.1175/jpo2793.1

Cited by 17 publications

(17 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence variability in barotropic boundary current forcing induces an increase in the variability of T P , especially at interannual to decadal time scales, with respect to variability induced by changes in buoyancy forcing alone. The flattening of the spectrum at high frequency is consistent with the MOC spectrum in AOGCMs as shown by Deshayes and Frankignoul (2005) and Zhu et al (2006). Indeed, in these studies, the MOC is defined in depth coordinates, hence its fluctuations are represented by changes in the dense water transport in the DWBC, that is to say T P in our simple model.…”

Section: Numerical Experimentssupporting

confidence: 86%

Mechanisms of variability in a convective basin

Deshayes¹,

Straneo²,

Spall³

2009

J Mar Res

Self Cite

View full text Add to dashboard Cite

An idealized model for a convective basin is used to investigate the mechanisms of variability of the formation and export of dense water. In this model, which consists of two isopycnic layers, dense water formation is induced by surface buoyancy loss in the interior, which is at rest. Newly formed dense water is transmitted to the surrounding boundary current through parameterized eddy fluxes. Variability in the formation and export of dense water is due to changes in the two main drivers: variations in the surface buoyancy fluxes and variations in the large-scale wind via a barotropic boundary current. Numerical integrations of the nonlinear model, with parameters and forcings corresponding to the Labrador Sea, show that the rate of dense water formation in the interior of the basin is strongly affected by changes in the buoyancy forcing, but not significantly affected by seasonal to interannual changes in the wind-driven barotropic boundary current. The basin tends to integrate the buoyancy forcing variability with a memory time scale set by eddies, which is decadal for the Labrador Sea. Variability in dense water export, on the contrary, is strongly affected by changes in the wind-driven barotropic boundary current but hardly affected by changes in buoyancy forcing. Indeed changes in the transport of dense water at the basin outflow are dominated by those at the basin inflow, which, in this model, are directly related to fluctuations in the wind-driven barotropic boundary current. These results, which are consistent with analytical solutions of the linear model, suggest that fluctuations in the surface buoyancy fluxes in the interior Labrador Sea have little impact on the interannual variability of the dense water transport by the Deep Western Boundary Current at the outflow of the Labrador Sea, which is dominated by fluctuations in the wind-driven North Atlantic subpolar gyre, but influence the formation and export of recently ventilated waters.

show abstract

Section: Numerical Experimentssupporting

confidence: 86%

Mechanisms of variability in a convective basin

Deshayes¹,

Straneo²,

Spall³

2009

J Mar Res

Self Cite

View full text Add to dashboard Cite

show abstract

“…This is consistent with Yeager and Danabasoglu (2014), who found that late-twentieth-century interannual-todecadal Atlantic circulation variability as simulated in an ocean-sea ice hindcast configuration of CCSM4 was almost entirely explained by subpolar forcing. It may reflect that the equator acts as a low-pass filter (buffering effect) for overturning circulation anomalies driven at high southern (or northern) latitudes (Johnson and Marshall 2002; see also Deshayes and Frankignoul 2005).…”

Section: Atmospheric Forcing Of the Amocmentioning

confidence: 99%

Wintertime Atmospheric Response to North Atlantic Ocean Circulation Variability in a Climate Model

2015

Self Cite

View full text Add to dashboard Cite

Maximum covariance analysis of a preindustrial control simulation of the NCAR Community Climate System Model, version 4 (CCSM4), shows that a barotropic signal in winter broadly resembling a negative phase of the North Atlantic Oscillation (NAO) follows an intensification of the Atlantic meridional overturning circulation (AMOC) by about 7 yr. The delay is due to the cyclonic propagation along the North Atlantic Current (NAC) and the subpolar gyre of a SST warming linked to a northward shift and intensification of the NAC, together with an increasing SST cooling linked to increasing southward advection of subpolar water along the western boundary and a southward shift of the Gulf Stream (GS). These changes result in a meridional SST dipole, which follows the AMOC intensification after 6 or 7 yr. The SST changes were initiated by the strengthening of the western subpolar gyre and by bottom torque at the crossover of the deep branches of the AMOC with the NAC on the western flank of the Mid-Atlantic Ridge and the GS near the Tail of the Grand Banks, respectively. The heat flux damping of the SST dipole shifts the region of maximum atmospheric transient eddy growth southward, leading to a negative NAO-like response. No significant atmospheric response is found to the Atlantic multidecadal oscillation (AMO), which is broadly realistic but shifted south and associated with a much weaker meridional SST gradient than the AMOC fingerprint. Nonetheless, the wintertime atmospheric response to the AMOC shows some similarity with the observed response to the AMO, suggesting that the ocean-atmosphere interactions are broadly realistic in CCSM4.

show abstract

“…Less complex models can help elucidate how anomalies of the MOC propagate throughout the global oceans (see, e.g., Wajsowicz and Gill 1986;Kawase 1987;Huang et al 2000;Johnson andMarshall 2002a,b, 2004;Cessi et al 2004;Deshayes and Frankignoul 2005;Liu and Alexander 2007;and references therein). Of particular relevance to the present study is the equatorial buffer mechanism identified by Johnson and Marshall (2002a), which restricts abrupt changes of the MOC to a hemispheric basin at high frequencies.…”

Section: Introductionmentioning

confidence: 99%

Eddy Formation in the Tropical Atlantic Induced by Abrupt Changes in the Meridional Overturning Circulation

Góes

Marshall

Wainer

2009

Journal of Physical Oceanography

View full text Add to dashboard Cite

The variability of the meridional overturning circulation (MOC) in the upper tropical Atlantic basin is investigated using a reduced-gravity model in a simplified domain. Four sets of idealized numerical experiments are performed: (i) switch-on of the MOC until a fixed value when a constant northward flow is applied along the western boundary; (ii) MOC with a variable flow; (iii) MOC in a quasi-steady flow; and (iv) shutdown of the MOC in the Northern Hemisphere. Results from experiments (i) show that eddies are generated at the equatorial region by shear instability and detached northward; eddies are responsible for an enhancement of the mean flow and the variability of the MOC. Results from experiments (ii) show a transitional behavior of the MOC related to the eddy generation in interannual-decadal time scales as the Reynolds number varies due to the variations in the MOC. In experiments (iii), a critical Reynolds number Re c around 30 is found, above which eddies are generated. Experiments (iv) demonstrate that even after the collapse of MOC in the Northern Hemisphere, eddies can still be generated and carry energy across the equator into the Northern Hemisphere; these eddies act to attenuate the impact of the MOC shutdown on short time scales. The results described here may be particularly pertinent to ocean general circulation models in which the Reynolds number lies close to the bifurcation point separating the laminar and turbulent regimes.

show abstract

Spectral Characteristics of the Response of the Meridional Overturning Circulation to Deep-Water Formation

Cited by 17 publications

References 36 publications

Mechanisms of variability in a convective basin

Mechanisms of variability in a convective basin

Wintertime Atmospheric Response to North Atlantic Ocean Circulation Variability in a Climate Model

Eddy Formation in the Tropical Atlantic Induced by Abrupt Changes in the Meridional Overturning Circulation

Contact Info

Product

Resources

About