中国北方干旱半干旱区降水的多年代际变化特征及其与太平洋年代际振荡的关系

基于最新版本的全球降水气候中心(Global Precipitation Climatology Centre Version 7,GPCC_V7)资料与欧洲中期数值预报中心20世纪再分析资料(ERA-20C)融合的百年尺度逐月降水资料(1901~2012年),运用集合经验模态分解方法(EEMD)、合成分析等方法系统分析了我国北方干旱半干旱区降水多年代际变化特征及与太平洋年代际振荡(PDO)之间的相互关系。结果表明:北方干旱半干旱区大多数区域降水都具有50~60年的平均变化周期,而PDO对大多数地区降水多年代际变化特征具有明显的调制作用;其中新疆北部和内蒙古北部的降水与PDO呈现出显著的正相关,而河套东西部地区的降水则与PDO的变化呈现显著负相关。进一步分析表明,当PDO为暖相位时,径向环流增强使得北冰洋水汽南下,当遇到低空北上的阿拉伯海域暖湿气流时,会造成新疆中南部的降水增多;另一方面,PDO暖相位时赤道西太平洋及印度洋区域通过对流加热的作用激发了太平洋—日本/东亚—太平洋(PJ/EAP)遥相关型的产生,这有利于渤海湾暖湿水汽输送至干旱半干旱区北部区域,增大降水概率;同时,当偏北和偏西气流在河套北部区域相遇时会形成降水中心。当PDO位于冷位相时,结论则反之。

Multi-decadal Variability of Precipitation in Arid and Semi-Arid Region of Northern China and Its Relationship with Pacific Decadal Oscillation Index

Based on GPCC_V7 (Global Precipitation Climatology Centre Version 7) and ERA-20C (European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the 20th century) monthly precipitation data, multi-decadal variability (MDV) of precipitation in arid and semi-arid region of northern China and the relationship between MDV and Pacific Decade Oscillation (PDO) are analyzed using ensemble empirical mode decomposition (EEMD) and composition analysis methods. The result shows that precipitation in arid and semi-arid region of northern China has a multi-decadal variability with an average period of about 50-60 years, which may be modulated by PDO. Precipitation in northern Xinjiang and the Inner Mongolia are significantly positively correlated with PDO, while that in eastern and western Ordos Loop region is significantly negatively correlated with PDO. Further study shows that meridional circulation intensifies during positive PDO phase, leading to more southward water vapor transport from the Arctic Ocean. As a result, precipitation in Xinjiang increases due to the convergence of cold, moist northwesterly flow from the Arctic Ocean and warm, moust southwesterly flow from Arabian Sea in southern Xinjiang. On the other hand, convective heating over the equatorial western Pacific Ocean and Indian Ocean leads to the Pacific Japan/East Asia-Pacific(PJ/EAP) pattern of teleconnection. It is favorable for the transport of moist airmass from Bohai Sea to its northern area and increases precipitation there during positive PDO phrase. Besides, the moist northerly flow from Bohai and westerly flow converges in the northern Ordos Loop area, where a maximum precipitation center forms. The situation is opposite during negative PDO phrase.