Intra-event Characteristics Of Stable Hydrogen And Oxygen Isotopes In Precipitation And The Relationship With Water Vapor Isotopes In Lanzhou City

Stable isotopes in precipitation record and preserve a large amount of information about environmental changes.The study of stable isotopes of precipitation in different time scales is an important basis for the application of stable isotopes to the study of water cycle,global climate change and atmospheric circulation.The intra-event scale can reflect the stable isotope changes in a short time more precisely.With the improvement of sampling technology,it is possible to conduct high-frequency continuous sampling for a single precipitation event.The study of stable isotopes of hydrogen and oxygen in precipitation on the event scale is helpful to explore their variation characteristics more precisely.In this study,a single continuous precipitation event in Lanzhou from June to October in the period of 2019to 2020 was collected with multiple frequency within event scale(10 min and 30min).Based on the precipitation isotope data and water vapor isotope data obtained during the sampling period,combined with the meteorological data,the precipitation isotope variation characteristics of Lanzhou events were studied in detail.The results show:(1)Through the variation of?¹⁸O in a single precipitation event,it is found that the?¹⁸O in the whole precipitation event presents regular patterns(“V”,“L”,descending and ascending patterns)and some cases without obvious rules.For the long-time weak precipitation event from June 26 to 27,2019,the change of?¹⁸O shows a typical“L”pattern,which does not follow the precipitation effect.For the short-time strong precipitation event on July 28,2019,the change of?¹⁸O is a typical downward trend,which shows a significant precipitation effect.In addition,the combined effects of westward water vapor,high latitude continental water vapor and local water vapor cycle lead to the isotopic changes of two typical precipitation events.(2)The slope and intercept of the meteoric water line obtained by collecting continuous precipitation samples are both smaller than the global meteoric water line,indicating that the raindrops are affected by secondary evaporation during the precipitation process and the local arid climate.Compared with the event-scale meteoric water line equation,the slope and intercept of the meteoric water line of continuous precipitation in intra-event are significantly higher.This is mainly because each set of data on the event scale is a mixture of different stages of a single precipitation,so each set of data on the intra-event scale is closely related to the change of a single precipitation process.(3)There are temperature effect and humidity effect on?¹⁸O in precipitation at event scale and intra-event scale.There is no precipitation effect in the intra-event scale precipitation.The d-excess is negatively correlated with temperature,positively correlated with precipitation amount and relative humidity in precipitation.(4)Through the study of the?¹⁸O of water vapor and precipitation in Lanzhou,it is found that they are positively correlated on a daily scale.The isotope exchange between atmospheric water vapor and raindrops can lead to a significant depletion of the isotope composition of water vapor,which in turn leads to the enrichment of isotopes in precipitation.In addition,the isotope control of atmospheric water vapor by the moisture source may be one of the reasons for the difference in observations,which in turn affects the isotope changes of precipitation.