Jet Configurations Leading to Extreme Winter Temperatures Over Europe

The North Atlantic eddy-driven jet (EDJ) is the main driver of winter weather in Europe and has often been described by its latitude or strength. Here, we show that the influence of the EDJ on European winter temperature extremes can be better characterized by a multiparametric perspective that accounts for additional aspects of the EDJ structure (tilt, zonal elongation, etc.). We identify four regions where extreme temperatures are distinctly associated with the EDJ: Scandinavia, Central Europe, Eastern Europe, and Western Mediterranean (WMED). Overall, the anomalous horizontal advection induced by blockings during cold spells and enhanced westerlies during warm events is the main mechanism leading to extreme event occurrence. However, diabatic processes play an important role in WMED region. Both processes generate asymmetric effects in minimum and maximum temperatures contributing to higher intensities of cold than warm events. These extreme events are associated with different EDJ configurations, which typically involve perturbed EDJs during cold spells and strong tilted EDJs during warm events, but with important variations depending on the region. In almost every region, the combined effects of more than two EDJ parameters yield significant increases in the probability of cold and warm events, suggesting an oversimplification of traditional approaches based on a single EDJ parameter. We show, using logistic regression models, that, although important, latitude and intensity are often unable to discriminate unequivocally the region of extreme event occurrence, and in some regions, they do not drive the largest changes in the odds of extremes. Weather and climate in Europe are mainly determined by strong winds flowing from the west, also called the North Atlantic jet stream. The jet influences the trajectories of air masses and is related to the occurrence of near surface temperature extreme events. In this work, we analyze the jet configurations associated with winter cold spells and warm events in different regions of Europe by using a decomposition of the jet structure on several parameters, including the intensity, latitude, longitude, tilt, and other zonal asymmetries. We identify four regions with differentiated responses to these jet parameters: Scandinavia, Central Europe, Eastern Europe, and Western Mediterranean. In all cases, the advection of cold and warm air masses is the leading mechanism of temperature extremes. However, this can occur under different jet configurations depending on the type of extreme and its region of occurrence. We show that other EDJ parameters apart from the traditional ones (latitude and intensity) are needed to fully characterize the probability and region of occurrence of temperature extreme events. The occurrence of European wintertime temperature extremes can be associated with a combination of a few eddy-driven jet parametersTypical parameters (latitude and intensity) are not always among the jet features driving the occurrence of extreme temperature eventsSkillful aspects of the jet vary with the type of extreme and region of occurrence