The influence of the North Atlantic Oscillation on the regional temperature variability in Sweden: spatial and temporal variations

ABSTRACT A statistical analysis of the seasonal and interannual variations in the regional temperature anomalies of Sweden during 1861–1994 is performed. The study uses homogenized monthly temperatures averaged over 6 regions to minimize the non climatic and local‐scale climatic effects. It is found that the temperature variability shows a clear regional and seasonal dependency. The topography, the influence of the sea and the synoptic climatology may have determined the dependency. The anomaly is related to variations in the North Atlantic Oscillation (NAO) expressed by an index (NAOI) and the extent to which the temperature anomaly can be explained by the NAO is investigated. The results show that the NAO has an important effect on the regional Swedish temperature on the monthly and interannual scales. The relationship between the temperature and NAOI over the period 1985–1994 are strong, implying that the NAOI may be a suitable candidate for a statistical downscaling model of the regional temperature. However, correlation analysis over different 31‐year periods shows that the strength of the association varies with time and region. The further north the weaker the association. On the other hand, the temporal variations of the moving correlations for the 6 regions are similar. Part of the temporal variations may be explained by the averaged strength of NAO during different 31‐year periods. This is especially evident for southern Sweden. At last, the coherency spectrums between the temperature anomalies and the NAO index is determined, which enables an examination of the association over the frequency domain. The result supports the idea that the NAO has an important effect on the Swedish temperature, though the strength of the association varied with time. These results have implications for statistical downscaling.