东北亚地区初夏、盛夏和传统夏季降水特征及环流型的异同性研究

A Study on Characteristics of Precipitation and Circulation Pattern in Early Summer, Midsummer and Conventional Summer in Northeast Asia

本文利用1979~2015年GPCP(Global Precipitation Climatology Project)逐月降水资料,采用经验正交函数(EOF)分解和Morlet小波分析方法,对东北亚地区初夏、盛夏和传统夏季降水的时空分布特征以及环流型开展了系统性的研究,揭示了东北亚地区传统夏季降水表现为盛夏降水贡献占主导,其年际和年代际特征以及环流特征同盛夏降水特征相一致,而初夏降水和盛夏降水特征及形成机制则具有显著差异。空间分布上,初夏的降水EOF第一模态表现为"+-+"的三极型分布,而盛夏和传统夏季则表现为南北相反的偶极型特征;时间演变方面,初夏降水表现为5~6 a振荡周期,盛夏为2~3 a为主的振荡周期,传统夏季则兼具上述两类振荡周期;在年代际调整方面,在1990年代末,盛夏降水和传统夏季降水在华北和东北地区发生了显著的年代际转折。此外,分析降水与环流的联系发现:初夏,由于西太平洋上空异常反气旋将西太平洋等地的水汽向北方地区输送,且受欧亚II型(EUII)遥相关的作用,东北亚地区初夏降水异常具有明显纬向特征。盛夏,东北亚地区降水主要受到西太平洋副热带高压西伸北进、孟加拉湾和南海等地水汽加强的影响。欧亚I型(EUI)遥相关和亚洲太平洋型(EAP)遥相关与我国东北以西和沿海地区的降水具有显著相关性。EU型遥相关的作用使东北亚夏季降水的异常中心存在西北—东南向的波列特征,EAP型遥相关的作用则使夏季降水存在经向三极型或偶极型特征。

Based on monthly Global Precipitation Climatology Project （GPCP） data from 1079 to 2015, temporal and spatial characteristics of precipitation and circulation patterns in early summer, midsummer and conventional summer in Northeast Asia are systematically investigated using empirical orthogonal function （EOF） analysis and Morlet wavelet methods. Results indicate that the conventional summer precipitation is dominated by midsummer precipitation. The interannual and interdecadal circulation variations are consistent with the characteristics of midsummer precipitation, while the mechanisms for early summer and midsummer precipitation are significantly different. Looking at the spatial distribution of precipitation, it is found that the first leading mode of early summer precipitation exhibits a ＂＋ -- ＋＂ tripole pattern along the meridional direction, while an opposite pattern is found in the first leading modes of midsummer and conventional summer precipitation. Early summer precipitation demonstrates a 5~5-a period and midsummer precipitation shows a 2-3-a period. In the late 1990s, midsummer precipitation and conventional summer precipitation experienced a significant decadal change in North China and Northeast China. Further analysis indicates that early summer precipitation anomalies are mainly zonally distributed, which is partly attributed to the water vapor transport to Northeast Asia by anomalous anticyclonic circulation over the Western Pacific and partly attributed to the effects of the Eurasian II teleconnection （EUII）. In midsummer, precipitation is mainly affected by the northward extension of western Pacific subtropical high and the strengthening of water vapor transport from the Bay of Bengal and the South China Sea. Eurasia I （EUI） teleconnection pattern and East Asia-Pacific （EAP） teleconnection pattern both are significantly correlated with midsummer precipitation in western China and the coastal area of China. Summer precipitation anomalies extend from northwest to southeast due to the effects of EUII teleeonnection pattern. The effect of EAP teleconnection pattern leads to the tripole or dipole patterns of summer precipitation distribution along the meridional direction.