The Local Precipitation Isotope Composition Is Indicative Of EI Nino Events

The El Ni?o-Southern Oscillation?ENSO?is the strongest signal of the interannual change of the tropical sea-air system.It can not only directly affect the weather and climate in the tropical Pacific,but also can indirectly affect the atmospheric circulation and precipitation and the temperature in Taiyuan.Here are many factors causing global climate anomalies,and there are complex interactions between various factors.Each time the El Nino event brings about different meteorological disasters during its occurrence.Based on precipitation isotope data and meteorological data from 2012 to2017 in the Taiyuan region,the NCL language and the HYSPLIT air mass back trajectory model were used to explore the role of precipitation stable isotopes in the 2014 strongest El Ni?o event.Through the study,the following conclusions are drawn:1.During the El Nino period,the meteorological variables in Taiyuan changed significantly.Decrease in precipitation on the annual scale.The annual precipitation decreases in the summer,and the precipitation slightly increases in the winter;the relative humidity increases in the whole year scale.The relative humidity in summer is reduced,and the relative humidity in winter?represented by RH,refers to the ratio of the mass of water vapor contained in a humid air to the mass of water vapor contained in a saturated air at the same temperature and pressure?;On the scale,the annual temperature dropped in 2014 and the temperature increased in 2015.The average temperature in the summer of the first half of the year decreased,and the average temperature in the winter half year increased?warm winter?.The change of average vapor pressure in Taiyuan City is consistent with the precipitation,and the vapor pressure decreases at the annual scale.2.During the El Ni?o period,water vapor transmission in Taiyuan changed significantly.During the summer of the EI Nino events,the water vapor transmission from the southeast direction of taiyuan was weakened,and the water vapor transmission of the western Pacific and westerly wind belt in the southwest was enhanced.In winter,the water vapor transmission from the westerlies is obviously enhanced,and the water vapor transmission from the southeast is weakened.At the same time,the summer months are less than wet,and the winter is more than wet.According to the analysis of the trajectory model after HYSPLIT air mass,during EI Nino,the flow of water vapor from the west wind belt and southwest direction increased by 10.55%and 6.44%respectively compared with the normal years.The water vapor transmission from the southeast was reduced by 10.23%compared with the normal year.3.The stable isotopic composition of precipitation in Taiyuan area during EI Nino was obviously changed.Through comparative analysis of 218precipitation samples during the period from 2012 to 2017 in Taiyuan City,it was found that during the El Nino event,the?¹⁸O and?D in Taiyuan were higher than normal years due to the low humidity in the water vapor transport process.Isotope erosion reduces.the d_excess of the surplus is also large,mainly because during the El Ni?o event,water vapor from the southeastern region with relatively high relative humidity decreased,and water vapor from the western region with relatively low relative humidity increased.In addition,the isotope data were subjected to regression analysis to obtain the atmospheric waterline equation of Taiyuan City:?D=7.37?¹⁸O+5.18?R²=0.936,n=218?.This equation is related to the slope and intercept of the global and Chinese atmospheric waterlines.In contrast,both the slope and the intercept are smaller,reflecting that the precipitation in Taiyuan may be affected by secondary evaporation,and the water vapor transport in Taiyuan area is mainly related to the westerly belt transport.4.The stable isotope composition of local precipitation has certain indicative effects on EI Nino events.Comprehensive analysis of the correlation of?¹⁸O with precipitation,relative humidity,and temperature during the period from2012 to 2017 in Taiyuan shows that there are precipitation effect and temperature effect in Taiyuan,and the correlation coefficient between?¹⁸O and relative humidity and temperature during the El Nino event is biased.high.There is a certain negative correlation between?¹⁸O and relative humidity,which may be influenced by secondary evaporation in the cloud.Based on the above relationship,precipitation stable isotope composition can be used to indicate the impact of EI Nino events.