Reconstruction of monthly 700,500 and 300 hPa goepotential height fields in the European and Eastern North Atlantic region for the period 1901-1947

Abstract

Gridded geopotential height (gph) fields at 700, 500 and 300 hPa were reconstructed back to 1901 based on sea level pressure, temperature and precipitation data over the European and Eastern North Atlantic region using canonical correlation analysis. Sensitivity analysis showed that the cumulative shared variance of the prefiltered (by means of principal component analysis) gph fields should be on the order of 95 to 99%, and for the predictors lower than 90%, in order to achieve reliable reconstructions. The obtained relations between the surface data and the gph fields were robust and the promising cross-validation results were revealed to be reproducible in a second independent period. The main mode of wintertime 700, 500 and 300 hPa gph field variability in the 20th century is a dipole pattern that clearly shows the signature of a regional representation of the Arctic Oscillation (AO). The time series of this mode of variability implied a strengthening of the gph gradients in the troposhere over Europe in the last decades of the 20th century; this is without precedent in the 20th century.