青藏高原冬春积雪异常对中国东部夏季降水频次和强度变化的影响

Impacts of Winter and Spring Snow Anomalies over the Tibetan Plateau on Summer Precipitation Frequency and Intensity in Eastern China

基于多种大气再分析和降水资料、青藏高原台站、卫星观测等高原冬春积雪资料,采用合成分析、相关分析、回归分析等多种数理统计以及理想数值模拟试验等方法,分析了青藏高原冬春积雪异常与中国东部夏季降水频次和强度变化的关联及可能原因。分析表明:(1)基于站点观测的高原积雪年际变化特征显著,大气再分析数据、卫星反演资料分析呈现出一致性变化趋势。(2)高原积雪异常对中国夏季降水频次与强度分布的影响具有显著的空间差异。高原冬春积雪偏多,使得我国华北、长江中下游地区夏季降水发生频次增加,但华北中雨和小雨类型的增加占比较大,而长江中下游地区则主要表现为大雨和暴雨发生频次增加的贡献。(3)积雪异常偏多年,高原热源作用减弱,500 hPa位势呈现清晰的“负—正—负”异常波列结构,西风急流位置偏南并加强,副高脊线偏南。在上述环流条件下,西北太平洋异常反气旋北侧的气旋性环流使得水汽输送停滞在长江中下游流域,伴随大气垂直运动增强,导致该区域强降水的强度增强、频次偏多;华北地区受“鞍型”场环流结构控制,虽然较小量级降水频次增加,但水汽输送较弱,降水强度变化不显著。上述研究结果,可为高原积雪异常相关的中国夏季降水变化及其短期预测提供预示性信号。

Based on various atmospheric reanalyses and precipitations,as well as the winter and spring snow data over the Tibetan Plateau obtained using gauged stations and satellites,this study first compares and validates the consistency of changes in different snow data sets on the interannual scale.Then,the impact of winter and spring snow anomalies on the frequency and intensity of summer precipitation over eastern China are further explored.Moreover,combined with the atmospheric physical diagnosis and numerical simulation,the possible causes of spatial differences in the impact of snow anomalies on summer precipitation in China are investigated.The results of this study show the following:(1)The variation in the snow depth observed by gauged stations is consistent with that derived from the satellite data on the interannual variation scale.(2)The impact of Plateau snow anomalies on the frequency and intensity of summer precipitation in China exhibit significant spatial differences.During heavier snow during winter and spring in the Tibetan Plateau,the frequency of summer precipitation increases significantly in North China,the middle and lower reaches of the Yangtze River,and Northeast China.In contrast,the increase in the rainfall frequency in North China is mainly dominated by moderate and light rain in contrast with the increase in the heavy rain frequency in the middle and lower reaches of the Yangtze River.(3)In the years with heavier snow cover,the heat source over the Tibetan Plateau is weakened,resulting in the“negative–positive–negative”abnormal wave train structure on the 500 hPa potential height,the strengthened and southward westerly jet,and the southward subtropical high ridge.Under the influence of the above circulation background,the anomalous cyclonic circulation in the north of the anomalous anticyclone in the northwestern Pacific enhances the water vapor transport in the middle and lower reaches of the Yangtze River basin.With the strengthened atmospheric vertical movement,the intensity and frequency of heavy precipitation are increased in this region.However,North China is controlled by the circulation structure of the“saddle”field;the occurrence frequency of small precipitation increases significantly,whereas the water vapor transport is weak,and changes in the precipitation intensity are not significant.