| Water vapor is one of the most active atmospheric components and is the material basis in forming precipitation.Using the stable isotopes in atmospheric water vapor,one can more comprehensively analyze the origins of water vapor as well as its transport path,condensation and recharge forms in the water cycle,and more in-depth understand the water cycle process and its feedback mechanism.This paper analyzes the variational characteristics of the stable isotopes in the integrated atmospheric water vapor between 825hPa and 464hPa,in atmospheric water vapor of near surface in Changsha station and their influencing factors,and investigates the interaction of the stable isotopes in atmospheric water vapor with in precipitation,based on the global HDO and H2O data in atmospheric water vapor retrieved by the Tropospheric Emission Spectrometer(TES)from September,2004 to December,2009,and stable vapor isotopic data in atmospheric water vapor of near surface in Changsha station located in the monsoon zone derived from the real-time monitoring activities of water vapor isotope analyzers using Off-Axis Integrated Cavity Output Spectrometer(OA-ICOS)from October,2014 to September,2016.In the mean while,the corresponding stable isotopic data in precipitation is also included.The results show that:(1)The spatial distribution of mean annual ?vD with its mean annual seasonality in the global atmospheric water vapor presents the obvious zonal distribution and the land-sea difference.On the average,from the low latitudes to the high latitudes,?vD gradually decreases,and along the same latitudes,the ?vD in the continental regions are higher than the oceanic areas.In terms of the seasonality of ?vD,in general,there are above zero in the areas from 20° to 30°N and the southern hemisphere,and below zero in the other regions.Along the same latitudes,the absolute values of the seasonal difference of ?vD in the continental regions are higher than that in the oceanic areas.Overall,comparing with other regions,the variations of the mean annual ?vD and its seasonal difference with the latitude and underlying surface are distinct in the low latitudes.(2)The spatial distribution of the global mean annual ?vD is coincident with the spatial distribution of the mean annual ?pD observed by the Global Netwok of Isotopes in Precipitation(GNIP),with a linear correlation coefficient 0.51.15 typical stations is chosen in order to contrast the temporal variations of ?vD and ?pD,10 of them have a consistent trend,and the linear correlation coefficient is significant at the 0.1 level,but the linear relationship between the temporal variations of ?eD and ?vD is not significant or absent in other stations.(3)Affected by distinctive moisture sources,the ?D and ?18O in atmospheric water vapor of near surface in Changsha station exhibit obvious seasonal variability.More specifically,the average value of ?vD and ?v18O in the summer half year(April to September)is-97.78‰,-14.14‰,respectively,while the average value is-80.00‰,-12.49‰ in the winter half year(October to March),respectively.In the diurnal cycle,owing to the surface evapotranspiration and atmospheric turbulence etc,the results show that the stable vapor isotopes have distinct diurnal variations with higher ?v18O in night than in daytime.(4)Under synoptic scale,there are marked negative correlation between ?v18O and ambient temperature,precipitation amount and absolute humidity in Changsha station,and the linear correlation coefficients are-0.23,-024 and-0.30,respectively.However,in the diurnal cycle,the relationships between ?v18O and meteorological elements is distinct in precipitation days and no-precipitation days.In precipitation days,the diurnal variation of ?v18O is opposed to that of temperature and absolute humidity,whereas in no precipitation days,although the diurnal variation of ?v18O remains in contrast with that of temperature,it is almost in accordance with the changes of absolute humidity.(5)Affected by recycling of new precipitation and the falling raindrops,the ?18O in atmospheric water vapor is always lower than that in precipitation at Changsha station,and their difference ?? varies from 1.24‰ to 15.55‰,the average value is about 8.70‰.Furtherly,by modeling under equilibrium fractionation between liquid and vapor phase,stable vapor isotopes and precipitation isotopes are in or near the equilibrium state in precipitation days throughout the sampling periods,except for the periods from December,2014 to March,2015.(6)The Meteoric Water Line(MWL)in Changsha station is:?pD = 8.45?p18O+16.06,has a higher slope and intercept than Global Meteoric Water Line(GMWL),which indicated that it had the climatic characteristic of humid and rainy in Changsha.The Meteoric Vapor Line(MVL)is:?vD = 7.64?18O + 12.77,the slope and the intercept of this equation reflect the influence of the recycling of the local Furtherly,both the slope of the MVL and the MWL have some relevance with the local meteorological elements.On the average,along with the increase of the precipitation amount,the slope of the MVL and the MWL increase as well.Yet with the increase of the temperature and the relative humidity,the slope of the MVL still increases,contrast with the decreasing trend in the MWL. |
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