Contrasting interannual variability of atmospheric moisture over Europe during cold and warm seasons

Seasonality in the interannual variability of atmospheric moisture over Europe is investigated using precipitable water (PW) from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data set for 1979–2004. Over Europe the summer PW and its interannual variability (expressed by standard deviations) are essentially larger than those of the winter season. The largest seasonal differences are found over eastern Europe and European Russia, where the summer PW climatology and magnitudes of its interannual variability exceed respective winter characteristics by a factor of 2.5–3.8. The first and second empirical orthogonal function (EOF) modes of winter PW over Europe are associated, respectively, with the North Atlantic Oscillation (NAO) and the East Atlantic teleconnection pattern. During summer the leading EOFs of PW are not linked to the known regional teleconnection patterns. Our analysis revealed that EOF-1 of summer PW is associated with sea level pressure (SLP) pattern characterized by two action centres of opposite polarity over northwestern Siberia and over a broad region including southern Europe, the Mediterranean Sea and part of northern Africa. The EOF-2 of summer PW is associated with cyclonic/anticyclonic SLP anomalies over Scandinavia and southwestern Europe. It is shown that PW and precipitation variability are positively coupled during the cold season but not for the warm season. Instead, during the warm season we found a significant link between regionalPWand air temperature variability, indicating an important role of local heating in variability of summer PW over Europe