The East Atlantic Oscillation: Mechanism and Impact on the European Climate in Winter

Abstract

The second leading mode of principal component analysis of the winter atmospheric pressure pattern in the North Atlantic-European region known as the East Atlantic Oscillation (EAO) is considered. The winter EAO pattern exhibits well-defined dipole at 500-hPa geopotential height (H500) with centers over the North Atlantic and the Central Europe. The EAO phase-to-phase shifts reflect the general atmospheric circulation changes and the zonal (meridional) circulation dominates in positive (negative) EAO phase. This induces storm tracks spatial shift, heat and moisture transport redistribution, which in turn results in anomalous winter air temperature and precipitation in the Europe. The surface air temperature and precipitation interannual variability explained by EAO index is 25–35 % and 15–25 %, respectively. Positive EAO phase is associated with the higher winter air temperatures in Europe (mean anomalies are from +0.3 to +3.5 °C), and negative EAO phase is associated with the lower winter air temperatures (mean anomalies are from –1.5 to –0.5 °C). Basin-wide changes in the intensity and location of the North Atlantic polar jet stream are observed between the EAO opposite phases. Anomalous cyclonic (anticyclonic) circulation over the North Atlantic and southward (northward) shift of the North Atlantic jet stream is shown to be inherent in positive (negative) EAO phase.

Keywords

• East Atlantic Oscillation
• surface air temperature
• precipitation
• midtropospheric jet
• atmospheric circulation
• storm tracks