| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2004: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2003: ¥800,000 (Direct Cost: ¥800,000)
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| Research Abstract |
A number of studies are conducted for a climate change over the North Pacific around 1998/99, as well as climate studies which may be a basis of understanding of such a rapid climate change. Here, some major results are described.
The principal investigator of this research proposed previously that climatic regime shifts over the North Pacific appeared to be caused as synchronization between a 20-year oscillation and 50-70-year oscillation. In order to understand some basic mechanism of such resonance, a simple delayed oscillator model with periodic modulation of nonlinear feedback and that with periodic forcing are investigated. The basic mechanism of the nonlinear resonance associated with a concept of threshold has been clarified.
It was found that substantial changes of sea-ice occurred around 1998/99 in marginal seas around the North Pacific. In the Bering Sea, spring sea-ice reduced around 1999 in the eastern Bering Sea. This change was likely to be caused by a low-pressure anomaly
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over Alaska. In the Okhotsk Sea, although long-term trend of sea-ice reduction continued until the mid-1990s, in the late 1990s and the early 2000s, sea-ice areas were larger than usual. It was found that for this long-term fluctuation of sea-ice, atmospheric conditions in autumn, not in winter previous studies focused, are important.
For large-scale oceanic frontal zones, SST changes including those associated with 1998/99 change were investigated using a newly gridded high-resolution SST data (The dataset is available through the internet. You can find via google with "Minobe Maeda 1dg SST"). It was found that the subtropical front exhibited a large change in 1998/99, but not in the subpolar front. This is in contrast to the 1970s climatic regime shift, when a signal is more prominent in the subpolar front.
Also, it is found that the winter strength of the Aleutian Low, which is a major atmospheric circulation changes associated with the regime shifts, exhibits bimodality after removal of a linear trend. This suggests that the nonlinear feedback is important in the climate feedback underlying the regime shifts. Less
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