利用统计方法对印度洋偶极子(Indian Ocean Dipole, IOD)与华西秋雨的关系进行分析。结果发现:(1)相对于IOD的季节锁相特征, 华西秋雨与印度洋偶极子指数(Indian Ocean Dipole Index, IODI)相关性也呈现相应的变化特征:春、夏季正相关发展、范围扩大;秋季稳定且正相关性较高, 与夏季时滞相关较为一致;前期冬季减弱并呈反相关关系。(2)对印度洋偶极子时期异常环流场、水汽场以及射出长波辐射(Outgoing Longwave Radiation, OLR)场特征分析发现, IOD正位相年, 500 hPa高度场距平在冬、春季为负异常, 春、秋季西太平洋副热带高压偏强、偏北, 且夏季华西区域受中层异常浅槽的西南气流影响, 850 hPa经向风合成在冬、春季以负异常为主, 夏、秋季转为正异常, 且华西区域秋季为异常气旋性环流控制, 赤道印度洋低空东风异常, 这些异常环流都利于华西区域降水偏多, 并对偶极子的延续起到作用。(3)正位相年, 冬、春季华西大部区域为水汽辐散区, 夏、秋季四川东北部及黔渝大部为水汽辐合区, 水汽输送依靠孟湾西南气流和西太平洋副热带高压外围的偏东气流完成。(4)对应于印度洋海温正(负)异常, 秋季华西区域上空的热状况异常分布将使其大气对流增强(减弱)。因此, 夏季IOD异常位相为华西秋雨预报提供了一个有用的前期信号, 而秋季IOD正位相则对华西秋雨的发生发展起到较好的延续作用。
The relationship between the Indian Ocean Dipole(IOD) and autumn rainfall in West China was examined statistically. The results show as the seasonal lock of IOD, there is a significantly correlation between the Indian Ocean Dipole and the autumn rainfall in West China: positive correlation develops in spring and summer, and stable in autumn, it is consistent with the delays associated in summer, but the correlation weakens and inverse in early winter. During the occurrence of positive IOD episode, the southwest(cyclonic) anomalies in the middle(lower) troposphere over West China, and the equatorial easterly wind anomaly. These circulation anomalies are related to the above normal precipitation in West China. Moreover, during the occurrence of positive IOD episode, most areas of Huaxi are moisture divergence in winter and spring, but northeastern Sichuan, Guizhou and Chongqing are moisture convergence in summer and autumn, and the water vapor transport relying on the southwest air in Bay of Bengal and easterlies outside the Western Pacific subtropical. In positive IOD episode, OLR increased. The positive phase of the summer IOD provides a potential valuable signal for predicting the autumn precipitation in West China, and the positive phase of the autumn IOD play the role of continuation of development in autumn rainfall.
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