Do atmospheric teleconnection patterns explain variations and trends in thermal growing season parameters in Finland?

摘要

Using daily mean temperature datasets applied at regular grid points (10 x 10 km(2)) throughout Finland for the period 1961-2011, interannual variations and trends in thermal growing season (GS) parameters, in terms of start (GSS), end (GSE) and length (GSL) and their relationships with various atmospheric teleconnection patterns (ATPs) were analysed. The GSL in Finland naturally increases from north to south, in association with earlier GSS and later GSE. However, the results showed that during the last 50 years, GSL on national scale in Finland significantly (p < 0.05) increased, at a rate of 0.30 +/- 0.18 days year(-1). This change was mainly attributable to earlier GSS (0.16 +/- 0.13 days year-1, p < 0.05). The East Atlantic/West Russia (EA/WR) pattern was the most significant ATP influencing variations in GSS (rho = 0.33), GSE (rho =-0.42) and GSL (rho =-0.33) on national scale in Finland. Statistically significant (p<0.05) trends in GSL were all positive (increasing) and mainly observed in the centre (Oulu), upper east (Kuopio) andwest (Jyvaskyla), north (Rovaniemi-Sodankyla) and south-west coastal areas (Helsinki-Turku-Vaasa) of Finland. Increasing GSL in central, upper eastern and western Finland was mainly associated with significantly earlier GSS; that in the north with significantly later GSE; and that in the most south-westerly areas with both earlier GSS and later GSE. These increases in GSL and corresponding shifts in GSS and/or GSE were significantly correlated with the East Atlantic (EA) pattern in northern and central Finland; with the EA/WR pattern in the south, south-east and south-west; and with the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) in south-west coastal areas. The results provide a detailed national and spatial picture of changes in GS parameters in Finland during the last 50 years and reveal that the interannual variability in GS parameters in Finland is strongly linked with a number of ATPs, such as the EA, EA/WR, NAO and AO.