Forced and internal modes of variability of the East Asian summer monsoon
Forced and internal modes of variability of the East Asian summer monsoon
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DOI：
10.5194/cp-4-225-2008
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发表时间：
2008-11
影响因子：
4.3
通讯作者：
Jian Liu;Bin Wang;Jing Yang
中科院分区：
文献类型：
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作者：
Jian Liu;Bin Wang;Jing Yang
抽象的。利用现代观测资料（1979-2006），分析了东亚夏季风年际变化主要模态的动力结构和成因，并阐明了其与季节变化主要模态的根本区别。这些差异有助于理解东亚夏季风的强迫（比如轨道）和内部（比如年际）变率模式。我们发现，占总方差的39%左右的主导模态的年际变化，主要与主要厄尔尼诺的衰减阶段，而第二个模式，占总方差的11.3%，与发展阶段的厄尔尼诺/拉尼娜。东亚夏季风对ENSO的响应与厄尔尼诺的发展和衰减阶段呈非线性关系。这两种模态是由厄尔尼诺/拉尼娜强迫和季风-暖海洋相互作用决定的，或者基本上是由耦合气候系统内的内部反馈过程驱动的。在这种内部模态下，热带辐合带和东亚夏季风降水呈现出异相变化，长江流域梅雨与华北中部降水也呈现出异相变化。与此相反，太阳辐射强迫的年周期表现出ITCZ和副热带东亚夏季风降水之间的同相变化。此外，降水的季节性推进显示了从5月中旬到7月底的西南-东北倾斜雨带的大陆尺度北推进。印度季风和东亚季风之间的这种连贯的季节推进表明，华北中部夏季季风北方边缘的位置可能是强迫模式季风强度的足够测量。考虑到年模态与轨道变率具有相似的外部强迫，年周期和年际变化之间的差异可能有助于理解东亚夏季风变率在轨道时间尺度上和现代记录中的差异。
Abstract. The modern instrumental record (1979–2006) is analyzed in an attempt to reveal the dynamical structure and origins of the major modes of interannual variability of East Asian summer monsoon (EASM) and to elucidate their fundamental differences with the major modes of seasonal variability. These differences are instrumental in understanding of the forced (say orbital) and internal (say interannual) modes of variability in EASM. We show that the leading mode of interannual variation, which accounts for about 39% of the total variance, is primarily associated with decaying phases of major El Nino, whereas the second mode, which accounts for 11.3% of the total variance, is associated with the developing phase of El Nino/La Nina. The EASM responds to ENSO in a nonlinear fashion with regard to the developing and decay phases of El Nino. The two modes are determined by El Nino/La Nina forcing and monsoon-warm ocean interaction, or essentially driven by internal feedback processes within the coupled climate system. For this internal mode, the intertropical convergence zone (ITCZ) and subtropical EASM precipitations exhibit an out-of-phase variations; further, the Meiyu in Yangtze River Valley is also out-of-phase with the precipitation in the central North China. In contrast, the annual cycle forced by the solar radiation shows an in-phase variation between the ITCZ and the subtropical EASM precipitation. Further, the seasonal march of precipitation displays a continental-scale northward advance of a southwest-northeastward tilted rainband from mid-May toward the end of July. This coherent seasonal advance between Indian and East Asian monsoons suggests that the position of the northern edge of the summer monsoon over the central North China may be an adequate measure of the monsoon intensity for the forced mode. Given the fact that the annual modes share the similar external forcing with orbital variability, the difference between the annual cycle and interannual variation may help to understand the differences in the EASM variability on the orbital time scale and in the modern records.