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热带印度洋次表层偶极子模态及其1997/1998年过程诊断分析研究
TROPICAL INDIAN OCEAN SUBSURFACE DIPOLE MODE AND DIAGNOSTIC ANALYSIS OF DIPOLE EVENT IN 1997/ 1998
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摘要: 利用EOF分解及相关统计方法研究了热带印度洋400m以上的次表层海温异常并对1997/1998年热带印度洋偶极子事件过程进行诊断分析研究。结果表明:热带印度洋次表层400m以上的部分海温距平最大是在100m左右的深度, 就整个热带印度洋而言, 自20世纪80年代以来, 次表层60m以上出现了变暖的趋势, 而80m以下则出现了降温的趋势。同时在热带印度洋次表层80m深度存在着比海表更强的偶极子模态。1997/1998年发生在印度洋海表东冷西暖型的偶极子事件, 是东印度洋次表层的海温正距平西传的结果, 而海温正距平的西传与热带印度洋上东风异常有关, 其物理机制是东风异常激发的Rossby波的作用。Abstract: The tropical Indian Ocean subsurface temperature anomaly above 400 m is studied by using the method of EOF and other statistic methods, and the 1997/98 tropical Indian Ocean dipole event is analyzed.The results show that the largest temperature anomaly in the tropical Indian Ocean subsurface layer above 400 m is around the depth of 100 m.As for the whole tropical Indian Ocean, the subsurface layer above 60 m appears to have a warming trend since the 1980' s, while the subsurface layer below 80 m to have a cooling trend.The subsurface layer of 80 m has an obvious dipole mode, which is much stronger than that of the sea surface.In 1997/98, the dipole event of the sea surface in the Indian Ocean was resulted from the westward ex tension of the temperature anomaly over the eastern Indian Ocean.The westward ex tension of the temperature anomaly was related to the easterly anomaly over the tropical Indian Ocean, where the easterly anomaly might trigger the Rossby wave and induce the temperature anomaly to ex tend westward.
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Key words:
- Tropical Indian Ocean;
- Subsurface layer;
- Dipole mode;
- Temperature anomaly
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图 2 各海域区域平均后的次表层温度距平的均方差沿深度的垂直剖面图 (单位:℃)
(a) 热带印度洋地区:10°S~15°N, 50°E~110°E, (b) Nino3区:5°S~5°N, 150°E~90°W, (c) DMI
图 4 热带印度洋次表层温度距平作EOF分解得到的第一空间模 (EOF1) 和对应的时间序列 (图中阴影区为主分量PC1和海温异常相关达到95%显著性水平的区域)
(a)0m的EOF1, (b)0m对应的时间序列PC1, (c)80m的EOF1, (d)80m对应的时间序列PC1
图 6 不同月份的热带印度洋沿赤道海温距平的垂直剖面图 (阴影部分的区域海温距平绝对值超过了0.5℃)
(a)1996年11月, (b)1997年6月, (c)1997年12月, (d)1998年3月
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