Results of the coupled atmosphere-land surface model ECHAM5-JSBACH in NetCDF format

In this study we present first results of a new model development, ECHAM5-JSBACH-wiso, where we have incorporated the stable water isotopes H218O and HDO as tracers in the hydrological cycle of the coupled atmosphere-land surface model ECHAM5-JSBACH. The ECHAM5-JSBACH-wiso model was run under present-day climate conditions at two different resolutions (T31L19, T63L31). A comparison between ECHAM5-JSBACH-wiso and ECHAM5-wiso shows that the coupling has a strong impact on the simulated temperature and soil wetness. Caused by these changes of temperature and the hydrological cycle, the d18O in precipitation also shows variations from -4 permil up to 4 permil. One of the strongest anomalies is shown over northeast Asia where, due to an increase of temperature, the d18O in precipitation increases as well. In order to analyze the sensitivity of the fractionation processes over land, we compare a set of simulations with various implementations of these processes over the land surface. The simulations allow us to distinguish between no fractionation, fractionation included in the evaporation flux (from bare soil) and also fractionation included in both evaporation and transpiration (from water transport through plants) fluxes. While the isotopic composition of the soil water may change for d18O by up to +8 permil:, the simulated d18O in precipitation shows only slight differences on the order of ±1 permil. The simulated isotopic composition of precipitation fits well with the available observations from the GNIP (Global Network of Isotopes in Precipitation) database.本研究报道了新型耦合模式ECHAM5-JSBACH-wiso的首批研发成果。该模式在耦合大气-陆面模式ECHAM5-JSBACH的水文循环中，引入了稳定水同位素H₂¹⁸O与HDO作为示踪剂。本研究采用当代气候背景条件，在两种不同分辨率（T31L19、T63L31）下运行ECHAM5-JSBACH-wiso模式。通过对比ECHAM5-JSBACH-wiso与ECHAM5-wiso的模拟结果，发现该耦合过程对模拟气温与土壤湿度均存在显著影响。受气温与水文循环变化的驱动，降水中的δ¹⁸O出现了-4‰至4‰的波动。其中东亚东北地区的同位素异常最为显著：受区域气温升高影响，该区域降水中的δ¹⁸O亦同步升高。为分析陆面同位素分馏过程的敏感性，本研究开展了多组采用不同陆面分馏过程参数化方案的模拟试验并开展对比。通过这些模拟，我们可区分三种情景：无分馏过程、仅裸土蒸发通量包含分馏效应，以及蒸发与植物蒸腾（经植物输水过程）通量均包含分馏效应。尽管土壤水的δ¹⁸O可出现最高达+8‰的变化，但模拟得到的降水中δ¹⁸O仅存在±1‰量级的微小差异。模拟得到的降水同位素组成与全球降水同位素观测网（Global Network of Isotopes in Precipitation, GNIP）的实测观测数据吻合良好。