A cluster analysis of cold-season atmospheric river tracks over the North Atlantic and their linkages to extreme precipitation and winds

Using reanalysis and high-resolution ensemble simulations, we characterize cold season (December−March) North Atlantic (NA) atmospheric river (AR) tracks by grouping them into four distinct clusters; then for each cluster, we link the year-to-year variations in track count to large-scale climate variability and examine the climatological effects of the cluster on extreme precipitation and winds. The four clusters share similar prevailing AR track orientation, but differ in AR genesis locations and dominate over different regions. Cluster 1, with the longest average track of the four clusters, originates near the U.S. East Coast during La Niña and positive North Atlantic Oscillation (NAO) years and produces extreme precipitation and winds primarily over the eastern coast of North America. Cluster 2, which is weak in intensity and short-lived, forms north of 30°N of the open ocean during positive NAO years and contributes to more than 25% of the precipitation and wind extremes along the coasts of Northwestern Europe. Cluster 3, with the strongest intensity and longest duration among the four clusters, is generated surrounding the Gulf of Mexico during El Niño and negative NAO years and produces respectively more than 50% and 40% of the extreme precipitation and wind events over the eastern U.S. Cluster 4, the smallest and weakest among the four clusters, is favored under negative NAO conditions and generates roughly 25% of the extreme precipitation and winds along the coast of the Iberian Peninsula. The similarities and discrepancies between reanalysis and model simulations and among different member simulations are also discussed.