Impacts of ENSO and Indian Ocean Dipole Events on the Southern Hemisphere Storm-Track Activity during Austral Winter
Impacts of ENSO and Indian Ocean Dipole Events on the Southern Hemisphere Storm-Track Activity during Austral Winter
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DOI：
10.1175/jcli4155.1
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发表时间：
2007-07
影响因子：
4.9
通讯作者：
K. Ashok;H. Nakamura;T. Yamagata
中科院分区：
文献类型：
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作者：
K. Ashok;H. Nakamura;T. Yamagata
利用1979-2003年的观测资料和再分析资料，分析了ENSO和印度洋偶极子（IOD）现象对南半球冬季风暴轴活动的影响。偏相关技术被用来区分一个现象的影响，从其他的。在厄尔尼诺事件期间，副热带急流往往会大大加强，加强射流分叉，从而减少中纬度南太平洋和澳大利亚南部的风暴轨迹活动。当IOD为正值时，澳大利亚南部和新西兰部分地区的西风带和风暴路径活动也趋于减弱。因此，无论是积极的IOD，并在较小程度上，厄尔尼诺事件的行为，以减少冬季降雨量显着超过部分南澳和新西兰。大陆东南部和新西兰两个主要岛屿的北方部分的降水对IOD更为敏感。在塔斯马尼亚岛，与厄尔尼诺事件相关的降水量显着减少。相反，在南美洲中纬度地区，西风带和风暴轴活动的增强在正IOD事件中往往比在厄尔尼诺事件中更显着。结果表明，尽管从半球的角度来看，南半球环形模的主导影响，远程ENSO和/或IOD对当地风暴轴活动的影响，可以检测到在冬季作为一个重要的信号，特别是中纬度地区，包括南澳和新西兰。
Impacts of the ENSO and Indian Ocean dipole (IOD) phenomena on winter storm-track activity over the Southern Hemisphere are examined on the basis of the observed and reanalysis data for 1979–2003. The partial correlation technique is utilized to distinguish the impact of one phenomenon from that of the other. During an El Nino event, the subtropical jet stream tends to strengthen substantially, enhancing the jet bifurcation and thereby reducing storm-track activity over the midlatitude South Pacific and to the south of Australia. During a positive IOD event, the westerlies and storm-track activity also tend to weaken over southern Australia and portions of New Zealand. Thus both the positive IOD and, to a lesser extent, El Nino events act to reduce winter rainfall significantly over some portions of South Australia and New Zealand. Precipitation over the southeastern portion of the continent and over the northern portions of the two main islands of New Zealand is more sensitive to IOD. Significant reduction in precipitation associated with an El Nino event is seen over Tasmania. Over midlatitude South America, in contrast, the enhancement of the westerlies and storm-track activity tends to be more significant in a positive IOD event than in an El Nino event. It is demonstrated that despite the dominant influence of the Southern Hemispheric Annular Mode from a hemispheric viewpoint, the remote influence of ENSO and/or IOD on local stormtrack activity can be detected in winter as a significant signal in particular midlatitude regions, including South Australia and New Zealand.