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H. A. Dijkstra - One of the best experts on this subject based on the ideXlab platform.
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Multiple states in the late Eocene Ocean Circulation
Global and Planetary Change, 2018Co-Authors: Michiel Baatsen, A.s. Von Der Heydt, M. A. Kliphuis, Jan Viebahn, H. A. DijkstraAbstract:The Eocene-Oligocene Transition (EOT) marks a major step within the Cenozoic climate in going from a greenhouse into an icehouse state, with the formation of a continental-scale Antarctic ice sheet. The roles of steadily decreasing CO2 concentrations versus changes in Ocean Circulation at the EOT are still debated and the threshold for Antarctic glaciation is obscured by uncertainties in global geometry. Here, a detailed study of the late Eocene Ocean Circulation is carried out using an Ocean general Circulation model under two slightly different geography reconstructions of the middle-to-late Eocene (38 Ma). Using the same atmospheric forcing, both geographies give a profoundly different equilibrium Ocean Circulation state. The underlying reason for this sensitivity is the presence of multiple equilibria characterised by either North or South Pacific deep water formation. A possible shift from a southern towards a northern overturning Circulation would result in significant changes in the global heat distribution and consequently make the Southern Hemisphere climate more susceptible for significant cooling and ice sheet formation on Antarctica.
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The global Ocean Circulation on a retrograde rotating earth
Climate of The Past, 2011Co-Authors: V. Kamphuis, S. E. Huisman, H. A. DijkstraAbstract:Abstract. To understand the three-dimensional Ocean Circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global Ocean Circulation. This Circulation, often referred to as the Conveyor state, is characterised by an Atlantic Meridional Overturning Circulation (MOC) with a deep water formation at northern latitudes and the absence of such a deep water formation in the North Pacific. This MOC asymmetry is often attributed to the difference in surface freshwater flux: the Atlantic as a whole is a basin with net evaporation, while the Pacific receives net precipitation. This issue is revisited in this paper by considering the global Ocean Circulation on a retrograde rotating earth, computing an equilibrium state of the coupled atmosphere-Ocean-land surface-sea ice model CCSM3. The Atlantic-Pacific asymmetry in surface freshwater flux is indeed reversed, but the Ocean Circulation pattern is not an Inverse Conveyor state (with deep water formation in the North Pacific) as there is relatively weak but intermittently strong deep water formation in the North Atlantic. Using a fully-implicit, global Ocean-only model the stability properties of the Atlantic MOC on a retrograde rotating earth are also investigated, showing a similar regime of multiple equilibria as in the present-day case. These results indicate that the present-day asymmetry in surface freshwater flux is not the most important factor setting the Atlantic-Pacific salinity difference and, thereby, the asymmetry in the global MOC.
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The global Ocean Circulation on a retrograde rotating earth
Climate of the Past Discussions, 2010Co-Authors: V. Kamphuis, S. E. Huisman, H. A. DijkstraAbstract:Abstract. To understand the three-dimensional Ocean Circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global Ocean Circulation. This Circulation, often referred to as the Conveyor state, is characterized by an Atlantic Meridional Overturning Circulation (MOC) with deep water formation at northern latitudes and the absence of such deep water formation in the North Pacific. This MOC asymmetry is often attributed to the difference in surface freshwater flux: the North Atlantic is a basin with net evaporation, while the North Pacific receives net precipitation. This issue is revisited in this paper by considering the global Ocean Circulation on a retrograde rotating earth, computing an equilibrium state of the coupled atmosphere-Ocean-land surface-sea ice model CCSM3. The Atlantic-Pacific asymmetry in surface freshwater flux is indeed reversed but the Ocean Circulation pattern is not an Inverse Conveyor state (with deep water formation in the North Pacific) as there is strong and highly variable deep water formation in the North Atlantic. Using a fully-implicit, global Ocean-only model also the stability properties of the Atlantic MOC on a retrograde rotating earth are investigated, showing a similar regime of multiple equilibria as in the present-day case. These results demonstrate that the present-day asymmetry in surface freshwater flux is not a crucial factor for the Atlantic-Pacific asymmetry in the global MOC.
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Stability of the Global Ocean Circulation: Basic Bifurcation Diagrams
Journal of Physical Oceanography, 2005Co-Authors: H. A. Dijkstra, Wilbert WeijerAbstract:Abstract A study of the stability of the global Ocean Circulation is performed within a coarse-resolution general Circulation model. Using techniques of numerical bifurcation theory, steady states of the global Ocean Circulation are explicitly calculated as parameters are varied. Under a freshwater flux forcing that is diagnosed from a reference Circulation with Levitus surface salinity fields, the global Ocean Circulation has no multiple equilibria. It is shown how this unique-state regime transforms into a regime with multiple equilibria as the pattern of the freshwater flux is changed in the northern North Atlantic Ocean. In the multiple-equilibria regime, there are two branches of stable steady solutions: one with a strong northern overturning in the Atlantic and one with hardly any northern overturning. Along the unstable branch that connects both stable solution branches (here for the first time computed for a global Ocean model), the strength of the southern sinking in the South Atlantic changes su...
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A fully-implicit model of the global Ocean Circulation
Journal of Computational Physics, 2003Co-Authors: Wilbert Weijer, H. A. Dijkstra, Hakan Öksüzoǧlu, Fred Wubs, Arie C. De NietAbstract:With the recent developments in the solution methods for large-dimensional nonlinear algebraic systems, fully-implicit Ocean Circulation models are now becoming feasible. In this paper, the formulation of such a three-dimensional global Ocean model is presented. With this implicit model, the sensitivity of steady states to parameters can be investigated efficiently using continuation methods. In addition, the implicit formulation allows for much larger time steps than can be used with explicit models. To demonstrate current capabilities of the implicit global Ocean model, we use a relatively low-resolution (4° horizontally and 12 levels vertically) version. For this configuration, we present: (i) an explicit calculation of the bifurcation diagram associated with hysteresis behavior of the Ocean Circulation and (ii) the scaling behavior of the Atlantic meridional overturning versus the magnitude of the vertical mixing coefficient of heat and salt.
Jacques Verron - One of the best experts on this subject based on the ideXlab platform.
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the southwest pacific Ocean Circulation and climate experiment spice
Journal of Geophysical Research, 2014Co-Authors: Alexandre Ganachaud, Melissa Bowen, Sophie Cravatte, Neil J. Holbrook, Angelique Melet, Andreas Schiller, Bernadette M Sloyan, Matthew J Widlansky, Jacques VerronAbstract:The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean Circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin-scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua-New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Nino-Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ Oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter-intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions.
Angelique Melet - One of the best experts on this subject based on the ideXlab platform.
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the southwest pacific Ocean Circulation and climate experiment spice
Journal of Geophysical Research, 2014Co-Authors: Alexandre Ganachaud, Melissa Bowen, Sophie Cravatte, Neil J. Holbrook, Angelique Melet, Andreas Schiller, Bernadette M Sloyan, Matthew J Widlansky, Jacques VerronAbstract:The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean Circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin-scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua-New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Nino-Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ Oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter-intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions.
Alexandre Ganachaud - One of the best experts on this subject based on the ideXlab platform.
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the southwest pacific Ocean Circulation and climate experiment spice
Journal of Geophysical Research, 2014Co-Authors: Alexandre Ganachaud, Melissa Bowen, Sophie Cravatte, Neil J. Holbrook, Angelique Melet, Andreas Schiller, Bernadette M Sloyan, Matthew J Widlansky, Jacques VerronAbstract:The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean Circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin-scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua-New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Nino-Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ Oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter-intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions.
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Advances from the Southwest Pacific Ocean Circulation and climate experiment (SPICE)
2013Co-Authors: Alexandre Ganachaud, Melissa Bowen, Gary Brassington, Wenju Cai, Sophie Cravatte, Russ E. Davis, Lionel Gourdeau, Toshihiro Hasegawa, K Hill, Neil J. HolbrookAbstract:Endorsed by CLIVAR in 2008, the Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research project which aims to understand the southwest Pacific Ocean Circulation, as well as its direct and indirect influence on both regional and basin-scale climate, and the South Pacific Convergence Zone (SPCZ). SPICE was designed to measure and monitor the Ocean Circulation, and to validate and improve numerical models.
V. Kamphuis - One of the best experts on this subject based on the ideXlab platform.
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The global Ocean Circulation on a retrograde rotating earth
Climate of The Past, 2011Co-Authors: V. Kamphuis, S. E. Huisman, H. A. DijkstraAbstract:Abstract. To understand the three-dimensional Ocean Circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global Ocean Circulation. This Circulation, often referred to as the Conveyor state, is characterised by an Atlantic Meridional Overturning Circulation (MOC) with a deep water formation at northern latitudes and the absence of such a deep water formation in the North Pacific. This MOC asymmetry is often attributed to the difference in surface freshwater flux: the Atlantic as a whole is a basin with net evaporation, while the Pacific receives net precipitation. This issue is revisited in this paper by considering the global Ocean Circulation on a retrograde rotating earth, computing an equilibrium state of the coupled atmosphere-Ocean-land surface-sea ice model CCSM3. The Atlantic-Pacific asymmetry in surface freshwater flux is indeed reversed, but the Ocean Circulation pattern is not an Inverse Conveyor state (with deep water formation in the North Pacific) as there is relatively weak but intermittently strong deep water formation in the North Atlantic. Using a fully-implicit, global Ocean-only model the stability properties of the Atlantic MOC on a retrograde rotating earth are also investigated, showing a similar regime of multiple equilibria as in the present-day case. These results indicate that the present-day asymmetry in surface freshwater flux is not the most important factor setting the Atlantic-Pacific salinity difference and, thereby, the asymmetry in the global MOC.
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The global Ocean Circulation on a retrograde rotating earth
Climate of the Past Discussions, 2010Co-Authors: V. Kamphuis, S. E. Huisman, H. A. DijkstraAbstract:Abstract. To understand the three-dimensional Ocean Circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global Ocean Circulation. This Circulation, often referred to as the Conveyor state, is characterized by an Atlantic Meridional Overturning Circulation (MOC) with deep water formation at northern latitudes and the absence of such deep water formation in the North Pacific. This MOC asymmetry is often attributed to the difference in surface freshwater flux: the North Atlantic is a basin with net evaporation, while the North Pacific receives net precipitation. This issue is revisited in this paper by considering the global Ocean Circulation on a retrograde rotating earth, computing an equilibrium state of the coupled atmosphere-Ocean-land surface-sea ice model CCSM3. The Atlantic-Pacific asymmetry in surface freshwater flux is indeed reversed but the Ocean Circulation pattern is not an Inverse Conveyor state (with deep water formation in the North Pacific) as there is strong and highly variable deep water formation in the North Atlantic. Using a fully-implicit, global Ocean-only model also the stability properties of the Atlantic MOC on a retrograde rotating earth are investigated, showing a similar regime of multiple equilibria as in the present-day case. These results demonstrate that the present-day asymmetry in surface freshwater flux is not a crucial factor for the Atlantic-Pacific asymmetry in the global MOC.
