东亚水循环中水稳定同位素的GCM模拟和相互比较

GCM Simulation of Stable Water Isotopes in Water Cycle and Intercomparisons over East Asia

利用引入稳定同位素循环的ECHAM4、GISS E和HadCM3模式的模拟,对东亚降水中年平均δD和过量氘d的空间分布以及大气水线(MWL)进行了分析.根据模拟的空间分布,降水同位素在很大程度上反映不同气团的地理背景以及它们之间的相互作用,模拟结果很好地再现了由GNIP实测资料得到的降水稳定同位素的纬度效应、大陆效应和高度效应特征.在对降水d的模拟试验中,3个GCM的模拟均显示降水d具有较显著的纬度分布规律.在东亚地区,根据GCM模拟的MWL斜率与根据71个GNIP站点计算的MWL斜率之间的差值位在合理的估计范围之内.在对具有相对较长取样记录的12个GNIP站点局地大气水线(LMWL)的模拟试验中,LMWL的斜率和截距大致分布在一个合理的范围,但大多被高估.造成斜率和截距被高估可能原因与数据的覆盖范围和长度、模式中水循环过程的细节、模式的精度、降水量的模拟以及对云中冰面过饱和度的假设有关.

In this paper,the performance of three selected isotope incorporated GCMs,ECHAM4,GISS E and HadCM3 are examined by comparing the model results with GNIP observations.The spatial distribution of mean annual δD and mean annual deuterium excess d in precipitation,and the relationship between δ18O and δD in precipitation,are compared between GCMs and GNIP data over East Asia.Overall,the three GCMs reproduce major characteristics of δD in precipitation as observed by GNIP.The simulated d distributions are less consistent with the GNIP results.This may indicate that kinetic fractionation processes are not appropriately represented in the isotopic schemes of GCMs.The GCM modeled MWL slopes are close to the GNIP derived MWL,but the simulated MWL intercepts significantly overestimate the GNIP one.This supports that the three isotope incorporated GCMs may not represent the kinetic fractionation processes well.In term of LMWLs,the simulated LMWL slopes are similar to those from GNIP observations,but slightly overestimate for most locations.Some isotopic functions（especially those related to kinetic fractionation） and their parameterizations in GCMs may have caused the discrepancy between the simulated and GNIP observed results.Future work is recommended to improve isotopic function parameterization on the basis of the high-resolution isotope observations.