春季青藏高原感热对中国东部夏季降水的影响和预测作用

Impact of the spring sensible heat flux over the Tibetan Plateau on summer rainfall over EastChina and its role in rainfall prediction

利用1980—2012年青藏高原中、东部71个站点观测资料、全中国756站的月降水资料、哈得来中心提供的HadISST v1.1海温资料以及ERA-Interim再分析资料,综合青藏高原的感热加热以及全球海温,研究了春季青藏高原感热对中国东部夏季降水的影响,并建立预报方程,探讨了青藏高原春季感热对中国降水的预报作用。结果表明,青藏高原春季感热与中国东部降水关系密切,青藏高原春季感热异常增强伴随着长江流域中下游同期降水增多,后期夏季长江流域整流域降水也持续偏多,华南东部降水偏少。春季青藏高原感热的增强与环北半球中高纬度的罗斯贝波列密切相关,扰动在北太平洋形成的反气旋环流向西南方向延伸至西北太平洋,为长江流域输送大量的水汽,有利于降水的发生。夏季,伴随着前期青藏高原感热的增强,南亚高压位置偏东,西北太平洋副热带高压(西太副高)位置偏西偏南,西太副高北侧为气旋式环流异常。在西太副高的控制下,华南东部降水减少;西太副高西侧的偏南气流为长江流域带来大量水汽,并与来自北部气旋式环流异常西侧的偏北风发生辐合,降水增多。青藏高原春季感热异常是华南和长江流域夏季降水异常的重要前兆信号。加入青藏高原春季感热后,利用海温预报的华南、长江流域夏季降水量与观测值的相关系数有所提高,预报方程对区域降水的解释方差提高约15%。

By using observational data from71 stations over the central and eastern Tibetan Plateau,monthly rainfall data from756 rain gauges throughout China,HadISST v1.1 and ERA-Interim reanalysis data,impacts of the spring sensible heat flux over the Tibetan Plateau along with the global SST on rainfall over East China were investigated.The present study aims to improve the prediction skill of summer rainfall over China by using the sensible heat observations over the Tibetan Plateau in the preceding spring.Results show that there is a close relationship between the spring sensible heat flux over the Tibetan Plateau and rainfall over East China.When the upward sensible heat flux over the Tibetan Plateau increases in the spring,rainfall increases over the middle and lower Yangtze River valley in the spring and throughout the Yangtze River valley in the subsequent summer,whereas rainfall over Southeast China decreases.The increase of the sensible heat flux over the Tibetan Plateau concurs with a Rossby wave train along the middle-high latitudes of the northern hemisphere.The anticyclone robe over the North Pacific extends southwestward to the western North Pacific and transports abundant moisture to the Yangtze River valley.In the subsequent summer,the South Asian high shifts eastward and the western Pacific subtropical high shifts westward in the lower and middle troposphere,while a cyclonic anomaly occurs to the north.Under the control of the subtropical high,rainfall over Southeast China is inhibited;however,rainfall over the Yangtze River valley increases as abundant moisture is transported to this region by southerly flow to the west of the subtropical high.The southerly flow converges with the northerly flow to west of the cyclonic anomaly over the Yangtze River valley.The sensible heat flux over the Tibetan Plateau in the spring couldbe a key precursor of summer rainfall over Southeast China and the Yangtze River valley.With its impact considered,the rainfall predictions are highly consistent with observations,and the prediction skill of the summer rainfall increases by nearly 15%.