scholarly journals Impacts of the ocean lateral diffusion on the El Niño/Southern Oscillation-like variability of a global coupled general circulation model

2000 ◽  
Vol 27 (19) ◽  
pp. 3041-3044 ◽  
Author(s):  
S. Raynaud ◽  
S. Speich ◽  
E. Guilyardi ◽  
G. Madec
2007 ◽  
Vol 20 (5) ◽  
pp. 788-800 ◽  
Author(s):  
Andrew B. G. Bush

Abstract A sequence of numerical simulations with a coupled atmosphere–ocean general circulation model configured for particular times during the late Quaternary shows that simulated El Niño–Southern Oscillation (ENSO) events decrease in frequency from the Last Glacial Maximum (LGM) to today, in accord with linear stability theory, but increase in amplitude. Diagnostic analyses indicate that altered momentum fluxes from midlatitude eddy activity caused by changes in orbital forcing (in the Holocene) and topographic forcing (at the LGM) regulate the strength of climatological easterlies and therefore affect both the tropical mean state and the characteristics of interannual variability. The fact that climatic teleconnections associated with paleo-ENSO are fundamentally different during these times suggests a way in which to reconcile some of the existing discrepancies amongst interpretations of proxy records and numerical paleoclimate simulations.


2007 ◽  
Vol 20 (11) ◽  
pp. 2484-2499 ◽  
Author(s):  
Akio Kitoh ◽  
Tatsuo Motoi ◽  
Shigenori Murakami

Abstract Modulation of El Niño–Southern Oscillation at the mid-Holocene [6000 yr before present (6 ka)] is investigated with a coupled ocean–atmosphere general circulation model. The model is integrated for 300 yr with 6-ka and present (0 ka) insolation both with and without flux adjustment, and the effect of flux adjustment on the simulation of El Niño is investigated. The response in the equatorial Pacific Ocean in 6 ka is in favor of weaker El Niño variability resulting from lowered sea surface temperature (SST) and a more diffuse thermocline. Atmospheric sensitivity in 6 ka is larger than that in 0 ka because of increased trade winds, while oceanic sensitivity in 6 ka is weaker than that in 0 ka, resulting from destabilization of the upper ocean, both in the flux- and non-flux-adjusted experiments. However, the use of flux adjustment causes a difference in the total response. El Niño variability in 6 ka does not change much from that in 0 ka with the flux-adjusted case, while the 6-ka El Niño variability is weaker without flux adjustment. Because the observed proxy data suggest weaker El Niño variability in the mid-Holocene, the non-flux-adjusted version gives a more reasonable response despite a larger bias in its basic states, implying that nondistortion of sensitivity to forcing is more important.


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