Intraseasonal and seasonally persisting patterns of Indian monsoon rainfall
Intraseasonal and seasonally persisting patterns of Indian monsoon rainfall
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DOI：
10.1175/jcli3981.1
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发表时间：
2007-01-01
影响因子：
4.9
通讯作者：
Shukla, J.
中科院分区：
文献类型：
--
作者：
Krishnamurthy, V.;Shukla, J.
利用印度70年的高分辨率网格化日降水资料，研究了印度季风活跃期和间断期的时空结构。对降水异常的滞后合成进行了分析，结果表明：降水异常的活跃（中断）周期以正周期开始，平均寿命为16天;西高止山脉和印度中部东部的降雨异常，并在高峰期加强和扩大到覆盖印度中部和印度北部部分地区的地区，而负（正）异常覆盖喜马拉雅山以南地区和印度东南部。在活动（中断）期的最后阶段，正（负）降水异常向喜马拉雅山麓移动，而印度半岛则被相反的符号异常所覆盖。在活跃期和间歇期，该地区出现低压和低气压的天数与降雨分析一致。对日降水异常的多通道奇异谱分析表明，季风降水主要由两个周期分别为45和20天的季节内振荡和三个季节持续分量组成。45天和20天的振荡是活跃期和间歇期的表现，但对季节平均降水的贡献很小。季节性持续的组件与异常的相同的符号，并覆盖整个印度，有一个非常高的年际相关性与总的季节平均降雨量。这些结果支持季风降水年际变化的概念模型，包括季节平均分量和季节内变化的统计平均。季节平均降水量的预报成功与否取决于季节持续分量和季节内振荡的相对强弱。
The space-time structure of the active and break periods of the Indian monsoon has been studied using 70-yr-long high-resolution gridded daily rainfall data over India. The analysis of lagged composites of rainfall anomalies based on an objective categorization of active and break phases shows that the active (break) cycle, with an average life of 16 days, starts with positive (negative) rainfall anomalies over the Western Ghats and eastern part of central India and intensifies and expands to a region covering central India and parts of north India during the peak phase, while negative (positive) anomalies cover the sub-Himalayan region and southeast India. During the final stage of the active (break) period, the positive (negative) rainfall anomalies move toward the foothills of the Himalayas while peninsular India is covered with opposite sign anomalies. The number of days on which lows and depressions are present in the region during active and break periods is consistent with the rainfall analysis. The number of depressions during the active phase is about 7 times that during the break phase.Using multichannel singular spectrum analysis of the daily rainfall anomalies, the seasonal monsoon rainfall is found to consist of two dominant intraseasonal oscillations with periods of 45 and 20 days and three seasonally persisting components. The 45- and 20-day oscillations are manifestations of the active and break periods but contribute very little to the seasonal mean rainfall. The seasonally persisting components with anomalies of the same sign, and covering all of India, have a very high interannual correlation with the total seasonal mean rainfall. These results support a conceptual model of the interannual variability of the monsoon rainfall consisting of seasonal mean components and a statistical average of the intraseasonal variations. The success in the prediction of seasonal mean rainfall depends on the relative strengths of the seasonally persisting components and intraseasonal oscillations.