Active/break cycles: diagnosis of the intraseasonal variability of the Asian Summer Monsoon
Active/break cycles: diagnosis of the intraseasonal variability of the Asian Summer Monsoon
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DOI：
10.1007/s003820100161
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发表时间：
2001-11-01
期刊：
影响因子：
4.6
通讯作者：
Slingo, JM
中科院分区：
文献类型：
--
作者：
Annamalai, H;Slingo, JM
在这项研究中，各种诊断已应用于日常观测的出射长波辐射 (OLR) 和 ECMWF 再分析 (ERA) 产品，以提供与亚洲夏季季风相关的活跃/中断周期的全面描述，并解决季节内变化的两个主要时间尺度（10-20 天和 30-60 天）的不同行为。基于40天（30-60天）季内模式的全印度过滤日降雨量（AIR）的OLR综合分析表明，在活跃期，印度大陆上空对流显着增强，延伸到孟加拉湾、海洋大陆和赤道西太平洋，而赤道印度洋和西北热带太平洋上空对流受到抑制，导致印度洋上空形成“四极”结构。 亚洲季风域。为了响应这种加热模式，大规模哈德利（横向）和两个西偏（横向）热带环流得到增强。罗斯贝波的激发和传播也对温带环流产生重大影响。相比之下，15 天模式对于季风域来说更具区域性，并且对流具有显着的西偏方向。只有季风区上空的局地哈德利环流受此模态的调节。 POP（主振荡模式）分析揭示了这两种模式的演变，表明40天模式起源于赤道印度洋上空。一旦形成，它就会在赤道两侧向极地传播，并向东传播到赤道西太平洋。从赤道西太平洋开始，向北传播越过西太平洋和向西传播进入印度经线是突出的。传播特征是复杂且相互作用的，是复合材料中对流中“四极”结构的原因。根据 POP 系数时间序列评估的年际变化表明，40 天模式在所有年份的季风爆发阶段都很强，但整个季节的系统传播主要取决于海洋 TCZ（热带辐合带）的活动。 15天模式的POP分析表明，该事件起源于赤道西太平洋，与向西传播的罗斯贝波相关，在西北热带太平洋上空放大，同时调节印度经度上的大陆和海洋TCZ。这种模式在季风建立阶段很明显。由于两种季节内模式传播特征的复杂性，得出的结论是，要了解亚洲夏季季风（ASM）一个区域组成部分的次季节变化，需要了解整个 ASM 系统。
In this study, various diagnostics have been applied to daily observed outgoing longwave radiation (OLR) and ECMWF ReAnalysis (ERA) products to provide a comprehensive description of the active/break cycles associated with the Asian Summer Monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability, 10-20 days and 30-60 days. Composite analysis of OLR based on filtered daily All-India rainfall (AIR) for the 40 day (30-60 days) intraseasonal mode indicates that during active phases, convection is significantly enhanced over the Indian continent, extending over the Bay of Bengal, Maritime continent and equatorial west Pacific, while convection is suppressed over the equatorial Indian Ocean and northwest tropical Pacific, resulting in a 'quadrapole' structure over the Asian monsoon domain. In response to this heating pattern, the large-scale Hadley (lateral) and the two cast-west (transverse) tropical circulations are enhanced. There is also a significant impact on the extra-tropical circulation through excitation and propagation of Rossby waves. In contrast, the 15-day mode is more regional to the monsoon domain and has a prominent cast-west orientation in convection. Only the local Hadley circulation over the monsoon region is modulated by this mode. The evolution of these two modes as revealed by POP (principal oscillation pattern) analysis, shows that the 40-day mode originates over the equatorial Indian Ocean. Once formed it has poleward propagation on either side of the equator, and eastward propagation into the equatorial west Pacific. From the equatorial west Pacific, northward propagation over the west Pacific and westward propagation into the Indian longitudes are prominent. The propagative features are complex and interactive and are responsible for the 'quadrapole' structure in convection seen from the composites. The interannual variability, assessed from the POP coefficient time series, indicates that the 40-day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic TCZ (tropical convergence zone). The POP analysis of the 15-day mode indicates that this event originates over the equatorial west Pacific, associated with westward propagating Rossby waves, amplifies over the northwest tropical Pacific and modulates both the continental and oceanic TCZs over Indian longitudes simultaneously. This mode is pronounced during the established phase of the monsoon. Due to the complexity in the propagational features of both the intraseasonal modes, it is concluded that understanding the subseasonal variability of one regional component of the Asian Summer Monsoon (ASM), requires understanding the entire ASM system.