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Reliability of GCM (general circulation model) simulations is a significant predictor selection criteria and seems to be essential for outcomes of the statistical downscaling. This article investigates the reliability of a wide ensemble of CMIP5 climate models in reproducing seasonal atmospheric circulation patterns over Europe and the North Atlantic, namely sea level pressure (SLP) and 500 hPa geopotential height (G500). GCMs were evaluated with respect to 1971-2000 NCEP/NCAR reanalysis data by means of MAE, correlation coefficient and standard deviation. An attempt was made to determine the range of biases introduced into the statistical models by biases in the GCM simulations. For this purpose, canonical correlation analysis (CCA) models linking large-scale atmospheric circulation and air temperature in Poland were driven by historical GCM simulations expressed as anomalies with reference to the reanalysis data. It was shown that reliability of GCMs varies considerably, both seasonally and on an inter-model basis, thus becoming unfavourable in the context of statistical downscaling application. Overall, GCM ability to reproduce G500 values is better than for SLP. The most important finding from the statistical downscaling perspective is that SLP and G500 biases may introduce considerable air temperature biases (T-GCMbiases) into the downscaled reconstructions or projections of climate change. Seasonally, the highest T-GCMbiases were found in DJF, when a significant overestimation of air temperature results from a GCM tendency to overestimate the meridional pressure gradient. A similar situation appears to be a significant factor in MAM and SON. Multiyear average GCM biases do not, however, explain a significant part of the inter-model variability of T-GCMbias, thus highlighting the need for a more in-depth evaluation. Nevertheless, good GCM performance seems to ensure that T-GCMbias is not of a considerable value. Overall, the results of the article emphasise the necessity for undertaking an application-oriented assessment of GCM reliability prior to any statistical downscaling approach. [ABSTRACT FROM AUTHOR]

Analyzes the decadal variability of the Danube river flow in the lower basin and its connection with the North Atlantic Oscillation (NAO) for the period 1931?1995. Associated linkages with precipitation (PP) in the European sector, global sea surface temperature (SST) and atmospheric circulation for the period 1931?81, and the 500 hPa geopotential heights (G500) over the Northern Hemisphere for the period 1948?95 are also investigated. The results show that there is an out-of-phase relationship between the time series of the Danube river flow anomalies and the NAO index. The time series of a PP index presents a time evolution similar to that of the river flow anomalies. Correlation maps between the river flow anomalies and global SST show coherent large-scale patterns. Physically consistent sea level pressure and 500 hPa geopotential height are obtained.