S. Murakami

Japan Agency for Marine-Earth Science Technology, Yokohama, Kanagawa, Japan

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Publications (6)10.21 Total impact

  • Shigenori Murakami, Rumi Ohgaito, Ayako Abe-Ouchi
    Journal of the Atmospheric Sciences 03/2011; 68(3):533-552. · 2.67 Impact Factor
  • Journal of Climate - J CLIMATE. 01/2008; 21(19).
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    ABSTRACT: The ocean thermohaline circulation is important for transports of heat and the carbon cycle. We present results from PMIP2 coupled atmosphere-ocean simulations with four climate models that are also being used for future assessments. These models give very different glacial thermohaline circulations even with comparable circulations for present. An integrated approach using results from these simulations for Last Glacial Maximum (LGM) with proxies of the state of the glacial surface and deep Atlantic supports the interpretation from nutrient tracers that the boundary between North Atlantic Deep Water and Antarctic Bottom Water was much shallower during this period. There is less constraint from this integrated reconstruction regarding the strength of the LGM North Atlantic overturning circulation, although together they suggest that it was neither appreciably stronger nor weaker than modern. Two model simulations identify a role for sea ice in both hemispheres in driving the ocean response to glacial forcing.
    Geophysical Research Letters - GEOPHYS RES LETT. 01/2007; 341(12).
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    ABSTRACT: The simulation of the Atlantic thermohaline circulation (THC) during the Last Glacial Maximum (LGM) provides an important benchmark for models used to predict future climatic changes. This study analyses the THC response to LGM forcings and boundary conditions in nine PMIP simulations, including both GCMs and Earth system Models of Intermediate Complexity. It is examined whether the mechanism put forward in the literature for a glacial THC reduction in one model also plays a dominant role in other models. In five models the THC reduces during the LGM (by 5?40%), whereas four models show an increase (by 10?40%). In all models but one a reduced (enhanced) THC goes with a stronger (weaker) reversed deep overturning cell associated with the formation of Antarctic Bottom Water (AABW). It is found that a major controlling factor for the THC response is the density contrast between AABW and North Atlantic Deep Water (NADW) during the LGM as compared to the modern climate. More saline AABW is consistently found in all simulations, while all models but one show less cooling of AABW as compared to NADW. In five out of nine models a reduced (enhanced) THC during the LGM is associated with more (less) dense AABW at its source region, which in turn is determined by the balance between the opposing effects of salinity and temperature on the density of AABW versus that of NADW. The response in net evaporation over the Atlantic basin is relatively small in most models, so that changes in the freshwater budget are dominated by ocean transports. In only two models is the THC response during the LGM directly related to the response in net evaporation.
    Climate of the Past 01/2006; · 3.56 Impact Factor
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    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 equivalent to 10(6) ms(3) s(-1)) freshwater input in the northern North Atlantic, the multimodel ensemble mean THC weakens by 30% after 100 yr. All models simulate sonic 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.
    01/2006;
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    ABSTRACT: As part of the Coupled Model Intercomparison Project, integrations with a common design have been undertaken with eleven different climate models to compare the response of the Atlantic thermohaline circulation (THC) to time-dependent climate change caused by increasing atmospheric CO2 concentration. Over 140 years, during which the CO2 concentration quadruples, the circulation strength declines gradually in all models, by between 10 and 50%. No model shows a rapid or complete collapse, despite the fairly rapid increase and high final concentration of CO2. The models having the strongest overturning in the control climate tend to show the largest THC reductions. In all models, the THC weakening is caused more by changes in surface heat flux than by changes in surface water flux. No model shows a cooling anywhere, because the greenhouse warming is dominant.
    Geophysical Research Letters 01/2005; · 3.98 Impact Factor