Studies on Continental Hydrological Cycle Using Water Isotope Global Circulation Model

在CCSR/NIES大气环流模式（AGCM）的基础上，发展了一个水同位素全球环流模式（WI-GCM），该模式包括混合相云、降水滴蒸发和海洋蒸发的修正处理后的氢氧同位素全球环流。模拟的同位素比值与GNIP观测结果一致。在此基础上，用通量型半拉格朗日处理的网格基平流方案代替了大气中水分输送的数值计算方案。结果表明，这种替代方案不仅改善了极区水循环，而且改善了同位素比值的模拟，并将模拟结果与西藏、西伯利亚等地区的降水同位素比值观测结果进行了比较，表明同位素在研究水循环机制和变化规律方面具有一定的实用价值。在西藏地区，对流云的降水滴蒸发产生的水汽是重要的。在西伯利亚，观测到的同位素年际变化表明，陆-气循环过程的年际变化。在南极洲，通过对土壤和植物水同位素比值的观测结果与模式结果的比较，指出了土壤水同位素比值的年际变化与ENSO变化有关，并提出了进一步改进土壤水同位素比值的处理方法和利用地表蒸发进行土壤水分馏的重要性。结果表明，我们已经成功地建立了一个有效的土壤水同位素比值的定量分析工具利用水同位素研究水文循环。

A Water Isotope Global Circulation Model (WI-GCM) is developed based on CCSR/NIES Atmospheric General Circulation Model (AGCM) including global circulation of oxygen and hydrogen isotope with revised treatment of mixed-phase cloud, evaporation of precipitating drop, and evaporation from ocean. The simulated isotope ratio is found to be consistent with the results of GNIP observations. Further, thenumerical scheme of transport of water in the atmosphere is replaced by newly developed grid-base advection scheme with flux-form semi-Lagrangean treatment. It is found that this replacement of transport scheme improves not only the hydrological cycle of polar region but also the simulation of isotope ratio.Comparing the model results with observed isotope ratio in precipitation in Tibet, Siberia, and other regions, some utility of isotope for the study of mechanisms and variability of the hydrological cycle. In Tibet, an importance of water vapor which is originated from evaporation of precipitating drop from convective cloud is suggested. In Siberia, interannual variation of recycling process between land and atmosphere is suggested by observed interannual variation of isotope. In Antarctica, an interannualvariation of isotope ratio related with the interannual change of transport route connected with ENSO variation is identified.Comparing the observed water isotope ratio in the soil and plant with model results it is suggested that the improved treatment of soil water and fractionation by evaporation from land surface is important future study.It is concluded that we have succeeded in building a useful tool for the quantitative studies on hydrological cycle by using water isotope.