1998 Fiscal Year Final Research Report Summary
A Study of Decadal Variations in the Atmosphere and Oceans
| Project/Area Number |
08454130
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KIMOTO Masahide Center for Climate System Research, University of Tokyo, Associate Professor, 気候システム研究センター, 助教授 (30262166)
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| Co-Investigator(Kenkyū-buntansha) |
SHEN Xueshun Center for Climate System Research, The University of Tokyo, Research Associate, 気候システム研究センター, 助手 (40272538)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Decadal Variations / Coupled Ocean-Atmosphere Model / Ocean Subsurface Temperature |
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| Research Abstract |
This project used both observational and numerical approaches to study decadal to inerdecadal variations in the ocean-atmosphere system.
First, 30-50 year long observational data are used to describe global scale structures of ocean-atmosphere decadal variations. Coherent variations between the equatorial and extratropical Pacific regions are conspicuous. in addition, another decadal mode has been identified. This mode is related to an abrupt shift of the atmospheric general circulation and is characterized by a see-saw like oscillation between the arctic and mid-latitude regions in the Northern Hemisphere. A numerical experimentation showed that the significant delay of the snow season observed in the fall of 1989 in the eastern Eurasian continent contributed to the shift.
Oceanic variations are the key to the understanding of the decadal to interdecadal climate variability. However, the shortage of ocean subsurface data is serious. In this project, we produced a monthly ocean subsurfac
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e (0-500m) data set on a 1x1 deg. global grid, based on datasets collected by U.S.researchers combined with those from Japan Meteorological Agency, TOGA-TAO array, etc.
Observational data alone are not sufficient to elucidate the dynamics of decadal-interdecadal oscillations. Thereby, long-term integrations of coupled ocean-atmosphere numerical models are investigated. Pacific and Atlantic decadal oscillations that are similar to obsearvations have been identified. The Pacific oscillation is characterized by coherent variations between the tropics and extratropics as in observations. In the model, the pace maker of the decadal oscillation is the slow adjustment of the subtropical gyre and the extratropical-tropical interactions work to boost the decadal variance. A comparison shows that the principal processes responsible for the oscillations differ between the model and data. This is due to inadequacy of the model to resolve vertical structure of upper ocean currents. However, this excercise has lead us to propose mean-current advection and gyre adjustment as two possiblities that produce decadal oscillations. Less
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