Persistent winter merged jets over the Atlantic and extreme weather anomalies

Variabilities in the jet streams have a significant influence on our weather and climate, and could potentially increase the likelihood of a range of extreme weather events. The winter of 2009/2010 witnessed an unusual equatorward displacement of the Atlantic jet and its subsequent convergence with the African jet, leading to the emergence of a persistent zonally oriented merged jet. At the same time, intense and prolonged negative phase of the North Atlantic Oscillation (NAO) and unusually cold and extreme weather conditions were reported over the Northern Hemisphere. Such a merging was only observed to occur for a whole winter during the winters of 1968-69 and 1969-70. Preliminary results indicate that such persistent winter merged jets could be more frequent in a future global warming scenario and thus it is important to understand this dynamical regime transition of Atlantic jet and its effects on the weather patterns. In this study, we explore the extreme weather distribution over the northern hemisphere during such winter merged jets and its relation to NAO and ENSO. We show that merged jet winter months have a signature weather pattern distribution that is different from the negative NAO phase. We see a decrease in the surface eddy kinetic energy over the midlatitude during such winter leading to an equatorward shift in storm tracks over the Atlantic region and larger stormtrack density over the western Greenland which could potentially lead to the observed distribution of weather patterns. On comparing the surface temperature anomaly composites between the winters of strong negative NAO, EL Nino, and merged jet months we see that the merged jet winters have a significant persistent temperature distribution signature over the tropics and the Arctics. Similar analysis over the north hemisphere for surface wind, precipitation, and snowfall anomalies also shows a preferred persistent distribution over certain regions during the merged jet-state winters.