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CR 16:203-223 (2001)  -  doi:10.3354/cr016203

Impact of horizontal resolution on the simulation of seasonal climate in the Atlantic/European area for present and future times

Wilhelm May*

Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark

ABSTRACT: The climate response to increasing levels of atmospheric greenhouse gases, prescribed according to the Intergovernmental Panel on Climate Change (IPCC) scenario IS92a, is studied in 2 model simulations. One is a transient response experiment performed with a medium resolution (T42) coupled general circulation model of the atmosphere and ocean (ECHAM4/OPYC) developed at the Max Planck Institute for Meteorology. The other one is a time-slice experiment with the high resolution (T106) ECHAM4 model forced with monthly sea-surface temperatures and sea-ice from the coupled model. For two 30 yr time-slices, representing the present-day climate (1970-1999) and the future climate with an effective doubling of carbon dioxide (2060-2099), the seasonal mean climate statistics obtained from the 2 experiments in the Atlantic/European area are compared with each other and, for the simulations of the present-day climate, with observational data in order to evaluate the impact of the model¹s horizontal resolution on the simulation of regional climate change as well as on the quality of the simulation of regional climate. As the region of special interest, the Atlantic/European area is chosen. The model¹s horizontal resolution has a noticeable impact on the assessment of anthropogenic climate change as well as on the quality of the climate simulation at a local level, while at a regional level, that is considering the entire Atlantic/European area, the effect of the horizontal resolution is considerably reduced. The level of uncertainty related to the horizontal resolution actually falls with the range of uncertainty caused by the internal model variability obtained from ensembles of climate predictions. The level of uncertainty at a given location is very small for the near-surface temperature but somewhat higher for the sea-level pressure, in particular in autumn and winter, and relatively high for precipitation, with a marked maximum in summer. While the uncertainties in autumn and winter are mainly accounted for by the marked impact of the horizontal resolution on the dynamical aspects of the model, the high level of uncertainty in summer is related to the pronounced effect of the horizontal resolution on the model¹s physical parameterizations.

KEY WORDS: Climate change · Europe · General circulation model · Horizontal resolution · Precipitation · Sea-level pressure · Temperature

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