Persistent Model Biases in the Spatial Variability of Winter North Atlantic Atmospheric Circulation

Abstract

The three leading modes of the North Atlantic atmospheric circulation explain about 70% of the winter climate variability. Although climate models generally can capture these modes, biases may induce large uncertainties in regional climate predictions. Here, we evaluate the leading winter modes simulated by CMIP5-PMIP3 and CMIP6-PMIP4 models from the last millennium to future scenarios in comparison with historical reanalysis and paleo-reconstructions. The models generally have a good representation of the average spatial pattern of the North Atlantic Oscillation (NAO) while showing a larger spread in performance for the East Atlantic and Scandinavian patterns. In contrast to historical reanalysis, the simulated NAO pattern tends to be rather stationary under various climate states over the years 861–2100. Such underestimated spatial variability in the simulated NAO is directly related to the biased spatial shifts in NAO-related regional temperature and precipitation changes, inducing uncertainties in climate projections over the North Atlantic sector.