黄河中下游地区降水变化的周期分析

根据利用清代雨雪档案重建的黄河中下游及其4个子区域1736～2000年的逐年降水序列,采用小波变换方法,分析了该区降水变化的周期特征,探讨了影响降水周期变化的可能驱动因子.结果表明:黄河中下游地区的降水,具有2～4年、准22年及70～80年等年际与年代际的振荡周期.其中,2～4年周期与El Nino事件关联,在El Nino事件发生的当年或第二年,黄河中下游地区的降水比常年偏少;而准22年及70～80年的周期,与wolf太阳黑子相对数的周期变化及太平洋年代际振荡(PDO)信号有关.但在70～80年的周期尺度上,太阳活动与降水变化的对应关系在1830年以前表现为太阳活动偏强(弱)时,降水偏少(多);1830年以后,太阳活动的周期演变为80～100年的更长周期,因这一阶段可能受到由于人类活动加强而致的温室气体浓度升高等因素的干扰,太阳活动与降水之间的关系明显减弱;而PDO与降水的对应关系则表现在全时域上,且在近100多年,PDO与降水之间的相关关系逐渐加强,特别是在1940s以后达到最大.

Pr ecipitation Cycles in the Middle and Lower Yellow River

Based on the long-term precipitation series with annual time resolution in the middle and lower Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty,the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings,which drive the precipitation changes,are explored. The results show that the precipitation in the middle and lower Yellow River has inter-annual and inter-decadal oscillations like 2-4a,quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events,and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and 70-80a cycles,Wolf Sun Spot Numbers and Pacific Decadal Oscillation (PDO) coincide with the two cycle signals. However,on 70-80a time scale,the coincidence between solar activity and precipitation is identified before 1830,and strong (weak) solar activity is generally correlated to the dry (wet) periods; after 1830,the solar activity changes to 80-100a quasi-century long oscillation,and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover,in recent 100 years,PDO is becoming a pace-maker of the precipitation on 70-80a time scale.