SEASONAL MARCH OF THE EAST-ASIAN SUMMER MONSOON
SEASONAL MARCH OF THE EAST-ASIAN SUMMER MONSOON
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DOI：
10.1142/9789812701411_0001
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发表时间：
2004-11
期刊：
影响因子：
--
通讯作者：
Yihui Ding
中科院分区：
文献类型：
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作者：
Yihui Ding
本章对东亚夏季风的季节推进进行了全面的回顾。首先，从低层风场、高层风场、OLR场和降水场等方面讨论了南海和中南半岛夏季风爆发的最早期在5月中旬前后甚至更早。在发病前后，这些领域的突然变化被揭示出来。其特点是低层东风、高层西风向低层西风、高层东风转换，对流迅速发展，降水增多，副热带高压东移。中南半岛和南海夏季风爆发前，热带东印度洋和孟加拉湾的环流特征和对流活动发展。这些特征表现为一对穿越赤道的气旋的发展，低空西风带的迅速加速，对流的范围和强度都显著增强。气候上，夏季风的季节推进表现出明显的阶梯式向北和东北推进。在东亚地区，夏季风爆发和推进过程中存在两次突然的北跳和三个稳定期，而在西北太平洋地区，夏季风爆发和推进过程中存在三个阶段。东亚季风雨季，包括华南的前夏雨季、中国东部和日本的梅雨/白乌和朝鲜的昌马，通常都发生在夏季风北移的平稳期内，讨论了影响东亚季风雨季爆发和季节推进的主要物理过程和机制，着重讨论了三个控制因子及其相关的物理机制。海陆热力对比和青藏高原热源升高的影响是南海和中南半岛亚洲夏季风通过纬向温度梯度的快速逆转而突然爆发的先决条件。季节内振荡（ISO）的到来提供了一个触发机制，沿着几个锁相湿ISO阶段。南海北方、中南半岛半岛中部和北方的中纬度低槽入侵也是另一种触发机制，通过释放潜在不稳定度诱发对流活动，从而通过中尺度对流系统的反馈过程增强那里的季风槽。
This chapter presents a comprehensive review of the seasonal march of the East Asian summer monsoon. First, the earliest onset of the summer monsoon over the South China Sea (SCS) and the Indo-China Peninsula occurring around mid-May or even earlier, is discussed in terms of low-level and upper-level wind, OLR and rainfall fields. A sudden change in these fields before and after the onset is revealed. This is characterized by a wind switch from low-level easterlies and high-level westerlies to low-level westerlies and high-level easterlies, the rapid growth of convection and increase in rainfall, and the eastward retreat of the subtropical high. The onset of the summer monsoon over the Indo-China Peninsula and the SCS is preceded by the development of circulation features and convective activity in the tropical East Indian Ocean and the Bay of Bengal. These are characterized by the development of a twin cyclone crossing the equator, the rapid acceleration of low-level westerlies, and a significant increase in both the areal extent and the intensity of convection.Climatologically, the seasonal march of the summer monsoon displays distinct stepwise northward and northeastward advances. Over East Asia, two abrupt northward jumps and three stationary periods have been identified while over the western North Pacific three stages in the onset and advance of the summer monsoon have been identified. The noted East Asian monsoon rainy seasons, including the pre-summer rainy season over South China, Meiyu/Baiu over eastern China and Japan, and Changma over Korea occur normally during the stationary periods that are imbedded in the northward advance of the summer monsoon.Major physical processes and mechanisms responsible for the onset and seasonal progress are discussed with special emphasis on three controlling factors and related physical mechanisms. The land-sea thermal contrast and the effect of the elevated heat source of the Tibetan Plateau are identified as pre-conditions for the abrupt onset of the Asian summer monsoon over the SCS and Indo-China Peninsula through the rapid reversal of the meridional temperature gradient. The arrival of the intra-seasonal oscillations (ISO) provides a triggering mechanism, along with the several phase-locking wet ISO phases. The intrusion of mid-latitude troughs into the northern SCS and central and northern Indo-China Peninsula is also seen to be another triggering mechanism that induces the convective activity through the release of potential instability, thus enhancing the monsoon trough there through the feedback process of meso-scale convective systems.