"Extreme cold events over Europe during the 2011/12 winter and their link with the regime transition of the North Atlantic Oscillation" by Luo and Yao (Submitted to Geophys. Res. Lett.)
Abstract In this paper, a case study of the extreme cold European weather occurring during the 2011/12 winter is performed in order to provide a likely explanation for the outbreak of the extreme cold winter event. It is shown that the outbreak of the extreme cold European winter of 2011/12 is attributed to the regime transition of the North Atlantic Oscillation (NAO). When the NAO transits from a positive NAO (NAO) event to an Atlantic-European blocking (ENAO-) event, the decline of the surface air temperature is enhanced over the European continent as well as the precipitation anomaly is enhanced (reduced) in the Northern (Central) Europe. Moreover, it is further found that before the NAO regime transition the Atlantic storm track can exhibit an enhanced Atlantic-European storm track in the Central Europe along the northwest-southeast direction. However, after the NAO transition begins, this storm track can be split into two branches so as to establish double storm tracks due to the ENAO- anomaly feedback. The southern storm track in the Central Europe is weakened and its spatial distribution is similar to that before the NAO transition, while the northern one is enhanced along the poleward side of the Northern Europe. Because the ENAO- event is long-lived, the persistent double storm tracks can be maintained in the European continent to produce persistent low temperatures and precipitation over Europe. Thus, the persistent double storm tracks in the European continent are crucial for the outbreak of the 2011/12 Europe extreme cold weather.