A cluster analysis of the tracks of North Atlantic wintertime atmospheric rivers and links to extreme precipitation and winds

Atmospheric rivers (ARs) are filaments of anomalous water vapor transport that are capable of causing devastating precipitation and strong winds during landfall. To identify the impacts of different types of AR events to particular North Atlantic (NA) coastlines, a curve clustering method was employed to group the cold season (DJFM) NA AR tracks into four distinct clusters according to AR genesis locations and characteristics of subsequent tracks. The cluster analysis was performed to both one member of a set of high-resolution simulations (M01) and Japanese 55-year reanalysis (JRA-55), and the geographical distributions of track density of the four clusters in M01 bear remarkable resemblance to those in JRA-55. ARs of each cluster have focused impacts on a different region of NA. In M01, cluster 1 is modulated by negative SST anomalies in ENSO regions, mostly affecting the east coast of North America and northern Europe. Tracks in cluster 2 with the lowest track density, weakest intensity and shortest duration are governed by a negative polarity of NAO, making landfall to western Iberian Peninsula, Mediterranean Sea and northern Africa. Cluster 3 has the highest track density, impacting central-to-eastern U.S. likely during El Niño episodes. Cluster 4 is regulated by a positive phase of NAO and negative PNA pattern, striking northern and western Europe. To quantify the impacts of these four clusters, their associations to extreme precipitation and winds (defined as values above 98^th percentile at each grid point) are also investigated. The overall AR tracks identified in M01 account for over 80% (50%) of extreme precipitation (winds) along the entire east coast of U.S., with cluster 3 contributing to the largest portion of the percentage. Cluster 2 is responsible for about 30% of the extreme precipitation and 40% of the extreme winds along west coast of Iberian Peninsula. More than 30% of the extreme rainfall and 20% of the extreme winds along the west coast of northern Europe are subject to AR tracks in cluster 4.