A Mechanism of the Onset of the South Asian Summer Monsoon
A Mechanism of the Onset of the South Asian Summer Monsoon
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DOI：
10.2151/jmsj.81.563
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发表时间：
2003-06
影响因子：
3.1
通讯作者：
D. Minoura;R. Kawamura;Tomonori Matsuura
中科院分区：
文献类型：
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作者：
D. Minoura;R. Kawamura;Tomonori Matsuura
利用欧洲中期天气预报中心的再分析资料，我们检验了Kawamura等人提出的包含可能的海-气反馈过程的澳大利亚夏季风爆发机制是否也适用于南亚夏季风系统。在它们的机制中，海洋表面温度的升高和对大陆赤道一侧大洋附近600-850百帕水平层的干燥入侵，在加强爆发前潜在的对流不稳定方面发挥了至关重要的作用。结果表明，这种爆发机制适用于6月初印度夏季风的突然爆发，而不适用于5月中旬中南半岛最早爆发的夏季风。这与季风爆发的突发性在印度次大陆沿海地区最为明显的观测事实相一致。印度支那半岛的特点是起病相对较慢，尽管它的日期是最早的。起退机制之间过渡速度的不对称性也具有相似的区域特征。如果这一机制在印度次大陆和邻近海洋有效运作，预计印度夏季风的爆发将比东南亚夏季风的爆发延迟，因为由于陆地-海洋热对比增强导致的次大陆尺度热低外围的下沉抑制了对流。这可能是南亚夏季风系统中的两个主要起点明显不同的可能原因之一。
Using the European Centre for Medium-Range Weather Forecasts reanalysis data, we examine whether an onset mechanism of the Australian summer monsoon proposed by Kawamura et al., which incorporates possible air-sea feedback processes, can apply to the South Asian summer monsoon system as well. In their mechanism, a combination of the increase in sea surface temperatures and dry intrusion into the layer at 600-850 hPa level over the ocean off, the equatorial side of a continent, plays a crucial role in enhancing potentially convective instability prior to the onset. It is found that the onset mechanism is able to apply to the abrupt onset of the Indian summer monsoon at the beginning of June, rather than the earliest onset over the Indochina peninsula in middle May. This is consistent with the observational fact that abruptness of the monsoon onset is most evident over the coastal regions of the Indian subcontinent. The Indochina peninsula is characterized by a relatively slow onset, although its date is earliest. The asymmetry of the transition speed between the onset and retreat regimes also has similar regional features. If the mechanism operates efficiently on the Indian subcontinent and adjacent oceans, it is anticipated that the onset of the Indian summer monsoon is delayed, as compared to that over Southeast Asia because subsidence in the periphery of a sub-continental scale thermal low, resulting from intensification of land-ocean thermal contrast, inhibits convection. This may be one of the possible reasons why the two major onsets seen in the South Asian summer monsoon system are clearly distinguished from each other.