2000年后中国北方东部地区夏季极端降水减少及水汽输送特征

本文研究了1961～2016年中国北方东部地区夏季极端降水日数和极端降水贡献率的年代际变化特征,并进一步分析了该地区极端降水和普通降水的大气环流和水汽输送的差异。主要的研究结果表明:1961～2016年中国北方东部地区夏季极端降水日数和极端降水贡献率在2000年前后发生显著年代际变化,2000年后夏季极端降水天数和极端降水贡献率显著减少。与1984～1999年相比,2000～2016年在对流层高层从欧洲大陆、中亚到东北—蒙古地区,位势高度异常呈现出“正—负—正”的大气波列,从而造成北方东部地区上空为正压的位势高度正异常控制,伴随着下沉运动,大气层结趋于稳定,这些环流条件不利于极端降水发生。2000年后负位相的太平洋年代际振荡（PDO）和正位相的北大西洋多年代际振荡（AMO）共同加强了北方东部地区上空的正位势高度异常。进一步研究表明,极端降水与普通降水的水汽输送和收支以及关键的局地大气系统存在着显著差异,较普通降水而言,极端降水在南北向水汽输送和收支上更强;北方东部地区低空为较强的闭合低压控制,并不断受到高层高位涡空气下传的影响。

Decrease in Extreme Precipitation in Summer over East Northern China and the Water-Vapor Transport Characteristics after Year 2000

In this study, the authors investigated the interdecadal change characteristics of the extreme precipitation (days of extreme precipitation: R95p; contribution rate of extreme precipitation: R95t) in summer in ENC (East northern China) during the period 1961-2016, as well as the differences in the atmospheric circulation and transport of water vapor for extreme and ordinary precipitation. The results show that both R95p and R95t have decreased significantly since 2000. Compared with the period 1984-1999, in 2000-2016, there were three circulation anomaly centers located in the Eurasian, Central Asian, and Northeast China-Mongolian areas, which exhibited a “positive-negative-positive” wavelike structure that caused a predominant and positive barotropic anomaly over ENC. A positive high geopotential anomaly with a sinking movement is unfavorable for the occurrence of extreme precipitation in ENC. The negative phase of the Pacific Decadal Oscillation (PDO) and the positive phase of the Atlantic Multidecadal Oscillation (AMO) have jointly reinforced positive anomalies in the geopotential height over ENC. The research results further reveal that there have been significant differences in the water-vapor transport and the key local circulation systems of extreme and ordinary precipitation events. Compared with ordinary precipitation, the water-vapor transport and budget for extreme precipitation from south to north were stronger. In addition, the ENC area was controlled by a stronger closed low-pressure system, which could have been enhanced by descending air with high potential vorticity during the occurrence of extreme precipitation.