Results obtained with two versions of the Limited Area Model (LAM) ALADIN over differently sized integration domains (large, intermediate and small) in the European area are presented in order to investigate both the general model performance and the influence of domain choice on the quality of obtained results. The aim is also to illustrate the issues related to the strategy of selection of the optimal integration domain. Each of these studies has been performed with two versions of the ALADIN model: the first one is ALADIN-CLIMATE developed at CNRM/Météo-France, the second one is ALADIN-CLIMATE/CZ prepared at the Czech Hydrometeorological Institute (CHMI). This leaves us with total of six experiments forced by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 reanalysis data. The west Balkan domain covering Bulgaria is used as an evaluation region for investigation of the temporal and spatial properties of simulated precipitation and temperature fields. This region has been selected for its challenging orography making the results obtained here a valuable source for studies leading to further developments in climate modeling. It was found that size of the domain strongly affects the quality of obtained results. We have found that the largest domain reproduces the spatial characteristics of climate (such as bias) very well, but its use results in a poor representation of temporal aspects, which are however captured very well in experiments over both smaller domains. Our findings suggest that there is no optimal choice of domain size, securing the best results for both spatial and temporal evaluation. Our study also proves that model ALADIN can be efficiently used for climate research purposes, which together with its modest computational demands should make it as an attractive modeling choice for the Central and Eastern European climate research community. K e y w o r d s : ALADIN, climate modeling, domain size, ECMWF, ERA-40 reanalysis A. Farda et al. 314 Stud. Geophys. Geod., 54 (2010)

ABSTRACT. A multi-l ayered snow model, including most physical processes governing the evoluti on of snow packs, has been co upl ed to a globa l circul ati on model (GCM ) to improve the represe nta tion of snow cover in cl im a te simulations. The snow model (Crocus) includes o ri gin al feat ures to simul ate th e evolu tion of snowpaek layer ing that all ows a rea li stic calculation of snow albcdo as a function of the type and size of th e crys ta ls of the surface laye r. The coupling schcm e is based on a sy nchronous run of the GCM a nd of th e snow model with a n excha nge of the surface flu xes at eve ry tim e-step. It was tested in a fiv e-year run at a T4·2 resolution. The impact on th e atmosphere was important over most snow-covere d region s a nd th e snowpacks simul a ted in the differe nt regions present a layering that is realistic and very variable in co nnection with thc climate. The simul ated snow cover compares sati sfactorily with th e present snow clim atology.

ABSTRACT. A multi-l ayered snow model, including most physical processes governing the evoluti on of snow packs, has been co upl ed to a globa l circul ati on model (GCM ) to improve the represe nta tion of snow cover in cl im a te simulations. The snow model (Crocus) includes o ri gin al feat ures to simul ate th e evolu tion of snowpaek layer ing that all ows a rea li stic calculation of snow albcdo as a function of the type and size of th e crys ta ls of the surface laye r. The coupling schcm e is based on a sy nchronous run of the GCM a nd of th e snow model with a n excha nge of the surface flu xes at eve ry tim e-step. It was tested in a fiv e-year run at a T4·2 resolution. The impact on th e atmosphere was important over most snow-covere d region s a nd th e snowpacks simul a ted in the differe nt regions present a layering that is realistic and very variable in co nnection with thc climate. The simul ated snow cover compares sati sfactorily with th e present snow clim atology.

We investigated high-resolution simulations of regional climate models (RCMs) driven by ERA-40 reanalyses over areas of selected European countries (Austria, Czech Republic, Hungary, Slovakia and Romania) for the period 1961−1990. RCMs were run at a spatial resolution of 10 km in the framework of the CECILIA project, and their outputs were compared with the E-OBS dataset of gridded observations and RCM simulations at coarser 25 km resolution from the ENSEMBLES project to identify a possible gain from the CECILIA experiments over ENSEM-BLES. Cold biases of air temperature and wet biases of precipitation dominate in the CECILIA simulations. Spatial variability and distribution of the air temperature field are well captured. The precipitation field, relative to observations, often shows inadequately small spatial variability and lowered correlations but is nevertheless comparable to the ENSEMBLES model. Inter-annual variability (IAV) of air temperature is captured differently among seasons but mostly improved in CECILIA compared with ENSEMBLES. Precipitation IAV shows a similar or worse score. The detected weaknesses found within the validation of the CECILIA RCMs are attributed to the resolution dependence of the set of physical parameterizations in the models and the choice of integration domain. The gain obtained by using a high resolution over a small domain (as in CECILIA) relative to a lower resolution (25 km) over a larger domain (as in ENSEMBLES) is clear for air temperature but limited for precipitation.

Regional climate models (RCMs) are important tools used for downscaling climate simulations from global scale models. In project CECILIA, two RCMs were used to provide climate change information for regions of Central and Eastern Europe. Models RegCM and ALADIN-Climate were employed in downscaling global simulations from ECHAM5 and ARPEGE-CLIMAT under IPCC A1B emission scenario in periods 2021–2050 and 2071–2100. Climate change signal present in these simulations is consistent with respective driving data, showing similar large-scale features: warming between 0 and 3°C in the first period and 2 and 5°C in the second period with the least warming in northwestern part of the domain increasing in the southeastern direction and small precipitation changes within range of +1 to −1 mm/day. Regional features are amplified by the RCMs, more so in case of the ALADIN family of models.