下垫面蒸发和云中凝结分馏对降水稳定同位素影响的数值试验——空间分布的比较

利用稳定同位素大气水平衡模式（iAWBM），在一个水平衡和水稳定同位素平衡的框架下以及在相同的气象驱动下，模拟在不同的下垫面蒸发和不同的云中凝结分馏条件下降水中稳定同位素效应的空间分布特征，并通过与GNIP实测数据的比较以及模拟试验结果之间的相互比较，揭示云中的稳定同位素分馏和从下垫面蒸发的水汽同位素δ_e对降水中稳定同位素变化的可能影响，增进对全球水循环中稳定同位素效应的理解和认识。结果显示：iAWBM的4个模拟试验均很好地再现了全球降水中平均δ¹⁸O和平均δ¹⁸O季节差的空间分布特征；很好地模拟了降水同位素的温度效应、降水量效应的分布特点以及全球的大气水线MWL；比较而言，平衡分馏假设下模拟的全球降水中平均δ¹⁸O的空间分布与根据GNIP数据得到的实际空间分布以及模拟的全球MWL与实际MWL最接近，且模拟效果亦最好；动力分馏假设下模拟的降水中δ¹⁸O平均季节差的空间分布与根据GNIP数据得到的实际分布之间的相关程度较好，且拟合水平明显提高；在动力分馏和δ_e季节性的假设下，iAWBM再现全球δ¹⁸O-T和δ¹⁸O-P相关关系空间分布的能力较强。

Numerical tests on the impacts of surface evaporation and condensation fractionation on stable isotopes in precipitation:a comparison of spatial distribution

Using the isotope enabled atmospheric water balance model (iAWBM), the spatial variations of stable isotopic effects in precipitation is simulated under different condensation fractionation nature and surface evaporation inputs with the same weather forcing, in the framework of the water balance and stable water isotope balance, in order to reveal the impact mechanism of the in-cloud isotopic fractionation and vapor isotopic composition from surface evaporation on simulated precipitation isotopic characteristics, improve the understanding of the stable water isotope cycle in the globe, through the comparison between simulations and GNIP observations and intercomparisons among simulations. Results show that the distributional situations of mean δ¹⁸O and δ¹⁸O seasonality in precipitation simulated by four simulation tests are in good agreement with GNIP observations. The distributional characteristics of temperature effect and amount effect, as well as global MWL are well simulated. Comparatively, under the assumptions of equilibrium fractionation, simulated spatial distribution of mean annual δ¹⁸O and simulated global MWL are closer to GNIP observations, with the best fitting level. Under the assumption of kinetic fractionation, the correlation degree between simulated and observed spatial series of δ¹⁸O seasonality in precipitation is significantly enhanced, and the fitting level of simulation relative to observation improved. As the kinetic fractionation and δ_e seasonality are considered together, the ability of iAWBM reproducing global spatial distribution of δ¹⁸O-T and δ¹⁸O-P correlations is significantly enhanced.