Simulating the extreme 2013/2014 winter in a future climate

Abstract

AbstractHow would the spell of extreme weather observed over North America and western Europe during the 2013/2014 winter manifest itself in a warmer climate? Here a forced sensitivity method is used to calculate optimal model tendency perturbations which result in a simulation which has its upper atmospheric circulation shifted in the direction of the January 2014 jet stream pattern. When applied to a simulation run under present‐day conditions the main features of the observations of this event are reproduced, such as the more zonal position and increased strength of the midlatitude North Atlantic storm track, the anomalous temperature pattern over North America, and the excessive precipitation in parts of Europe. When this method is applied to a future warmer climate, the North Atlantic storm track changes to a more zonal orientation, but its strength does not see the significant increase that is obtained in the present‐day simulations. Despite southward advection of polar air into northeastern America, which has also occurred during the 2013/2014 winter, the associated drop in temperature is less in the future climate compared to the present‐day climate because of Arctic amplification. The less steep drop in temperatures over northeastern America leads to a smaller land‐sea temperature contrast, less baroclinic instability, and a reduced increase of midlatitude storminess. While one may expect the future increased atmospheric moisture content to augment the net precipitation, for this specific event, this effect is counterbalanced by the dynamics, leading to a similar net increase in precipitation in the future simulations compared to the present day.