基于卫星降水产品的华北北纬38°带降水氢氧同位素时空特征及水汽来源

Spatial and temporal variations of hydrogen and oxygen isotopes and sources of water vapour indicated from satellite precipitation products along the transection of 38°north latitude in North China

降水氢氧同位素的变化程度对反演降水水汽来源和认识蒸发作用的强弱有重要作用;结合高时间分辨率的卫星降水产品能够提高反演水汽来源的准确性,更清晰地说明水汽团的运移路径。本研究以位于华北北纬38°带的中国科学院太行山站(山区)、栾城站(山前平原)和南皮站(滨海低平原)2015—2018年降水氢氧同位素为对象,分析该区域降水水汽来源和极端降水对氢氧同位素的影响。结果表明:华北北纬38°带降水氢氧同位素在年内呈雨季富集、旱季贫化的特征,雨季降水氢氧同位素表现出随降水量增加而贫化的趋势;华北山前平原大气降水氢氧同位素拟合关系斜率和截距最小,说明山前平原降水受二次蒸发作用的影响最显著,蒸发作用也使得平原区枯水年同位素变幅最大,而山区雨量效应造成丰水年同位素变幅最大。利用卫星产品揭示降水的水汽来源,华北北纬38°带全年主导水汽为西北和内陆方向水汽,而雨季为西南和近缘海洋性水汽。由于水汽来源的变化,同时,山区和平原区分别受雨量效应和二次蒸发的影响,使得降水氢氧同位素在丰水年(2016)存在显著差异。用HYSPLIT模型模拟2016年"7·19"极端降水的路径,西南水汽是山区和平原区极端降水的主要水汽来源,而低平原区混合了东南向水汽。说明水汽源的差异及蒸发过程主导华北北纬38°带极端降水氢氧同位素的时空分布特征。

The variations of hydrogen and oxygen isotopes in rainfall are critical for understanding the sources of rainfall and the influence of local evaporation.Satellite precipitation products with high time resolution(for instance 1 h)could be helpful for testifying the accuracy of water sources,as it can clearly illustrate the route of cloud movement.In this study,we analyzed the composition of hydrogen and oxygen isotopes in different rainfall events in three stations from 2015 to 2018 along the transection of 38°N latitude from Taihang Mountains to the coastal region in North China,Taihang Mountain Station(mountainous area),Luancheng Station(pre-mountain plain)and Nanpi Station(coastal low plain).By selecting typical rainfall events,water vapor sources and its influence rainfall on hydrogen and oxygen isotopes were analyzed with hourly available CMORPH satellite precipitation products.Results showed that the hydrogen and oxygen isotopes of precipitation were cha-racterized by enrichment in the rainy season and depletion in the dry season.The hydrogen and oxygen isotopes in the rainy season showed a tendency of depletion with the increases of precipitation.The slope and intercept of the fitted relationship of hydrogen and oxygen isotopes in the piedmont region of the mountains were the lowest,indicating that precipitation in the piedmont plain was significantly affected by secondary evaporation fractionation.The effect of evaporation resulted in the largest variations of isotope ratio in the dry year.In the mountainous station,due to the heavy rainfall,large isotopic variation was found in rich precipitation year.Based on the route analysis of sate-llite precipitation products,dominant water vapor in the region was inland and northwest-oriented water vapor,while water vapor in the rainy season was from southwest and from the Pacific Ocean.There was a significant difference in the hydrogen and oxygen isotopes of precipitation in the mountainous and plain stations in 2016,owing to water vapor sources and effects of rainfall for the mountainous and evaporation for plain.The results from HYSPLIT model showed that during the rainstorm on 19 th July in 2016,water vapor at the mountainous station was mainly from the southwest,while that in the coastal plain was a mixture of southwest and southeast sources.Overall,our results showed that spatial and temporal variations of hydrogen and oxygen isotopes were controlled by both water sources and evaporation processes along the transection of 38°north latitude in North China.