Haese, Barbara; Werner, Martin; Lohmann, Gerrit (2013): Results of the coupled atmosphere-land surface model ECHAM5-JSBACH in NetCDF format. PANGAEA, https://doi.org/10.1594/PANGAEA.828264, Supplement to: Haese, B et al. (2013): Stable water isotopes in the coupled atmosphere–land surface model ECHAM5-JSBACH. Geoscientific Model Development, 6(5), 1463-1480, https://doi.org/10.5194/gmd-6-1463-2013
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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.
All simulations are run under present day conditions with a prescribed vegetation distribution over a simulation period of 10 years after a spin-up period of 2 years. The simulations are performed with AMIP-conform boundary conditions. The lower oceanic boundary condition for the atmospheric 18O isotopic composition is based on the dataset described by LeGrande and Schmidt (2006). The lower oceanic boundary condition for the atmospheric HDO is calculated via the observed relation for meteoric water on a global scale (Craig and Gordon, 1965). It is distinguished between the two resolutions: horizontal 3.8° x 3.8°, 19 vertical level (T31_xxx.nc) and horizontal 1.8° x 1.8°, 31 vertical level (T63_xxx.nc).
The implementation of fractionation processes over land surface varies between the experiments:
- xxx_noF_xxx.nc - no fractionation occurring during evapotranspiration
- xxx_FE_xxx.nc - fractionation occurring during evaporation only
- xxx_FET_xxx.nc - idealized setup where fractionation occurring during both evaporation and transpiration
- xxx_FEKxxx.nc - fractionation occurring during evaporation only, with different calculation of the kineticfractionation factor
The Experiments run with the coupled atmosphere-land surface model ECHAM5-JSBACH-wiso or with the atmosphere model ECHAM5-wiso (noF only).
- precipitation (aprt)
- isotopic composition of precipitation (wisoaprt_d)
- soil water depth (ws)
- isotopic composition of soil water (wisows_d)
- surface temperature (tsurf)
- temperature 2 m above surface (temp2),
- evapotranspiration (evap)
LeGrande, A. N. and Schmidt, G. A. (2006) Global gridded data set of the oxygen isotopic composition in seawater, Geophysical Research Letters, 33(12), L12604, doi:10.1029/2006GL026011
Craig, H. and Gordon, L. I. (1965) Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In: Stable Isotopes in Oceanographic Studies and Paleotemperature, edited by: Tongiorgi, E., 9-130, V. Lishi e F., Pisa, Italy, http://climate.colorado.edu/research/CG/
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