1995 Fiscal Year Final Research Report Summary
Geometrical Structure of Atmospheric Models and the Dynamical Basis of Weather Regimes and Blocking
| Project/Area Number |
06640560
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | Wakayama University |
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Principal Investigator |
ITOH Hisanori Wakayama Univ., Faculty of Education Associate Professor, 教育学部, 助教授 (80112100)
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| Co-Investigator(Kenkyū-buntansha) |
KIMOTO Masahide Univ.of Tokyo, Center for Climate System Research, Associate Professor, 気候システム研究センター, 助教授 (30262166)
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| Project Period (FY) |
1994 – 1995
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| Keywords | low-frequency / weather regime / blocking / low-frequency oscillation / chaotic itinerancy |
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| Research Abstract |
Using a quasi-geostrophic model with realistic topography, we had shown that chaotic itinerancy is the dynamical basis of weather regimes. Furthermore, long-period oscillations exist in each attractor or attractor ruin, which is the dynamical basis of low-frequency oscillations. This year, we have made these phenomena more realistic and have clarified another kind of low-frequency variability.
Changing a parameter in the model to unstable side, one regime (one attractor ruin, hereafter referred to as X) enlarges, while other regimes become obscure. These latter regimes are considered to correspond to real weather regimes. Amplitudes of low-frequency oscillations in X become large, which well explains real low-frequency oscillations.
EOFs 1 and 2 have dominant low-frequency variabilities. These correspond to real teleconnection patterns. The reason why these modes are dominant is as follows. Spatial patterns of EOF1 well coincide with those of the first eigenfunctions of the equation system linearized with respect to the time-mean state. The corresponding eigenvalues are very small. In other words, these patterns strongly respond to forcing, and the time changes are small.Thus, EOF1 is selected among many other patterns. This characteristic is guaranteed by the fact that geometrical structure around the time-mean state is "flat". It is also shown that this characteristic is not accidental but necessary.
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