Seasonal persistence and propagation of intraseasonal patterns over the Indian monsoon region
Seasonal persistence and propagation of intraseasonal patterns over the Indian monsoon region
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DOI：
10.1007/s00382-007-0300-7
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发表时间：
2008-03-01
期刊：
影响因子：
4.6
通讯作者：
Shukla, J.
中科院分区：
文献类型：
--
作者：
Krishnamurthy, V.;Shukla, J.
研究了印度次大陆、印度洋和西太平洋季风区对流的时空演化。对每日出射长波辐射的多通道奇异频谱分析得出了两种季节内振荡模式和两种大规模站立模式，作为季节内变化的最主要模式。振荡模式在大约 45 天和 28 天的时间尺度上变化，其平均变化周期与印度季风降雨活跃期和间歇期的生命周期相对应。在活跃（中断）周期期间，对流（干）异常带首先出现在赤道印度洋，随后扩大覆盖印度次大陆，最后在印度北部收缩消失。一些向东和向北的运动被发现与两种振荡模式相关，而向西的运动也可能与 28 天模式相关。振荡模式显示出具有延伸至西太平洋的大空间尺度。其中一种常备模态具有覆盖整个区域的统一符号异常，与厄尔尼诺和南方涛动（ENSO）模式有关。另一种常驻模态在赤道印度洋有一个偶极子结构，与印度上空的大规模异常相关，其符号与偶极子西部的异常符号相同。这两种站立模式在整个季风季节持续存在，每种模式都保持着各自的模式。季节平均季风主要由两种固定模式决定，振荡模态的贡献不大。站立模式（ENSO 模式和偶极模式）的相对作用似乎对于确定某些年份的季节平均值很重要。
The space-time evolution of convection over the monsoon region containing the Indian subcontinent, the Indian Ocean and the West Pacific has been studied. A multi-channel singular spectrum analysis of the daily outgoing longwave radiation has yielded two intraseasonal oscillatory patterns and two large-scale standing patterns as the most dominant modes of intraseasonal variability. The oscillatory modes vary on time scales of about 45 and 28 days and their average cycles of variability are shown to correspond to the life cycles of active and break periods of monsoon rainfall over India. During an active (break) cycle, a convection (dry) anomaly zone first appears in the equatorial Indian Ocean, subsequently expands to cover the Indian subcontinent and finally contracts to disappear in the northern part of India. Some eastward and northward movements are found to be associated with both oscillatory modes, while westward movement may also be associated with the 28-day mode. The oscillatory modes are shown to have a large spatial scale extending to the West Pacific. One of the standing modes has anomalies of uniform sign covering the entire region and is related to El Nino and southern oscillation (ENSO) pattern. The other standing mode has a dipole structure in the equatorial Indian Ocean associated with large-scale anomalies over India with the same sign as those over the western part of the dipole. These two standing modes persist throughout the monsoon season, each maintaining its respective pattern. The seasonal mean monsoon is mainly determined by the two standing patterns, without much contribution from the oscillatory modes. The relative role of the standing patterns (ENSO mode and dipole mode) seems to be important in determining the seasonal mean during certain years.