过去1500年典型暖期东亚夏季风年代际变化特征对比及其可能成因

利用通用地球系统模式开展的过去1500年气候模拟全强迫试验和对照试验结果,在验证模式模拟性能的基础上,采用多变量经验正交函数分解等方法,对比分析了典型暖期东亚夏季风年代际变化特征及其成因机制。结果表明,两个典型暖期东亚夏季风变化的主周期均为准10 a和准20 a。中世纪暖期黄河流域至日本南部一带降水偏多,长江流域以南和西北太平洋一带降水偏少;现代暖期东亚夏季风降水表现为“南涝北旱”型分布特征。内部变率是影响典型暖期东亚夏季风变化的主控因子之一,其中太平洋年代际振荡起决定性作用。当太平洋年代际振荡处于正位相时,热带西太平洋（东亚大陆）变暖（变冷）,东亚地区海、陆热力差减小,对应弱的东亚夏季风。另外,中世纪暖期海平面气压的动态变化对应850 hPa风场在西北太平洋（日本海）一带均出现了经向排列的异常反气旋（气旋）,从而导致中国南部（北部）降水偏多（偏少）。 

Comparison of the EASM interdecadal variability and possible causes between typical warm periods during the past 1500 years

The characteristics and causes of the East Asian summer monsoon (EASM) interdecadal variability during the Medieval Warm Period (MWP, 1001—1100 ) and Present Warm Period (PWP, 1901—2000) are examined by using results of all-forcing and control experiments over the past 1500 years of the Community Earth System Model version 1.0 (CESM1). Results show that the interdecadal variability of the EASM is characterized by a north-south dipole rainfall pattern in eastern China and the significant interdecadal periods of the EASM are around 10 and 20 years during both periods. These changes are mainly attributed to the internal variability, which is preliminarily dominated by the Pacific Decadal Oscillation. The positive phase of PDO induces warming (cooling) over the tropical western Pacific (East Asia continent), featuring a "colder land-warmer ocean" pattern, which favors a weak EASM. Besides, the meridionally arranged anomalous low-level anticyclone (cyclone) occurs over the northwestern Pacific (Sea of Japan) during MWP. These are dynamically in accordance with the sea level pressure, thus resulting in increased (reduced) precipitation over the southern China (northern China).