Descriptions and mechanisms for 1998/99 regime shift over the North Pacific

对1998/99年左右北太平洋的气候变化进行了一些研究，并进行了气候研究，这可能是理解如此迅速的气候变化的基础。这项研究的主要研究人员先前提出，北太平洋气候系统的变化似乎是由20年振荡和50-70年振荡之间的同步引起的。为了理解这种共振的一些基本机制，我们研究了一个简单的具有周期调制的非线性反馈和周期强迫的延迟振子模型。阐明了与阈值概念相关的非线性共振的基本机制，发现1998/99年前后北太平洋边缘海冰发生了显著的变化。在白令海，大约在1999年，白令海东部的春季海冰减少。这种变化很可能是由低气压异常…引起的在阿拉斯加上空。在鄂霍次克海，虽然海冰减少的长期趋势一直持续到1990年代中期，但在1990年代末和2000年代初，海冰面积比平时大。研究发现，对于这种海冰的长期波动，秋季的大气条件而不是以前的研究重点是冬季的大气条件是重要的。对于大尺度海洋锋区，利用新格式化的高分辨率海温数据(数据集可以通过互联网获得)，研究了海温的变化，包括与1998/99年变化相关的海温变化。你可以通过谷歌找到“Minobe Maeda 1DG SST”)。结果表明，1998/99年副热带锋变化较大，而副极锋变化不大。这与20世纪70年代气候系统的变化形成了鲜明对比，当时一个信号在次极锋区更为突出。此外，我们还发现，冬季阿留申低压的强度在去除线性趋势后呈现出双峰性。阿留申低压是与气候系统变化相关的主要大气环流变化。这表明非线性反馈在气候反馈中是重要的，气候反馈是气候变化的基础。较少

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 … More 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