On the decoupling of the IODZM from southern Africa Summer rainfall variability
On the decoupling of the IODZM from southern Africa Summer rainfall variability
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DOI：
10.1002/joc.2306
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发表时间：
2012-04
期刊：
影响因子：
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通讯作者：
D. Manatsa;C. Reason;G. Mukwada
中科院分区：
文献类型：
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作者：
D. Manatsa;C. Reason;G. Mukwada
印度洋偶极子/纬向模式（IODZM）从南部非洲的主导模式的降雨变率自1997年以来的解耦进行了研究。采用了以变异性作为观测时间序列主要描述参数的方法。这种方法可以通过检查印度洋盆地气候数据中的低频信号来识别不同的时期。分析期间从1922年到2008年，重点是10月至12月的季节，以捕捉最活跃的组成部分的IODZM事件，恰逢初夏降雨。1997/1998年前后是印度洋气候系统中一个重要的气候体制转变时期，而众所周知的1976/1977年气候转变在该区域的意义似乎较小。IODZM的统计参数的时间表现与西亚热带南印度洋的基本大气变量的时间表现显著匹配，并始终确定1961年和1997年为印度洋气候系统的重要转折点。然而，虽然相对较高的大气变量的变率迅速下降后，1997年，降水和IODZM时间序列变率的相应下降并没有被发现。相反，突然减少的两个时间序列之间的相关性到微不足道的值发生后，1997年。巧合的是，在1997年前的正IODZM事件期间，观察到南印度洋西部的显着冷却，随后在1997年之后的事件期间，西、东副热带南印度洋分别出现同步异常变暖和冷却。这一变化与1997年后南印度洋反气旋的东移有关。因此，1997年是印度洋气候系统中的一个重要年份，当一个不连续性的作用，从区域降雨变率的主导模式解耦的IODZM。皇家气象学会
The decoupling of the Indian Ocean Dipole/zonal mode (IODZM) from southern Africa's dominant mode of rainfall variability since 1997 is investigated. An approach of using variability as the major descriptive parameter for the observational time series is adopted. This approach enables the identification of epochs differentiated by the examination of low‐frequency signals in the climate data of the Indian Ocean basin. The period of analysis stretches from 1922 to 2008 and focuses on the October to December season so as to capture the most active component of the IODZM events that coincide with the early summer rainfall. The period around 1997/1998 is noted as an important climate regime transition in the Indian Ocean climate system whereas the well known 1976/1977 climate shift appears to be of lesser significance in the region. The temporal manifestation of statistical parameters of the IODZM matches significantly with those of basic atmospheric variables in the western subtropical South Indian Ocean and consistently identifies 1961 and 1997 as important turning points in the Indian Ocean climate system. However, although the relatively high variability of the atmospheric variables quickly decreases after 1997, a corresponding fall in the rainfall and IODZM time series variability is not found. Instead, an abrupt reduction in the correlation between the two time series to insignificant values occurs after 1997. Coincidentally, notable cooling over the western South Indian Ocean is observed during the pre‐1997 positive IODZM events, followed by a synchronized anomalous warming and cooling over the respective western and eastern subtropical South Indian Ocean during the events after 1997. This change is associated with an eastward displacement of the South Indian Ocean anticyclone after 1997. Thus, 1997 is a significant year in the Indian Ocean climate system when a discontinuity acts to decouple the IODZM from the dominant mode of regional rainfall variability. Copyright © 2011 Royal Meteorological Society