PNNL

Abstract

Atmospheric rivers (ARs), filaments of intense atmospheric moisture transport, play a significant role in delivering moisture poleward into the Arctic and triggering weather extremes. While previous studies have focused on large-scale circulations driving these events, this study investigates ARs through attributing their moisture sources using the Community Atmosphere Model version 5 (CAM5) with moisture-tagging capability. By separately examining ARs in the Atlantic and Pacific sectors of the Arctic, we reveal the receptor-dependent remote nature of their moisture sources. Unlike non-AR events, Arctic ARs primarily draw moisture from their respective ocean basins in lower-latitude regions during the cold season, and shift to land sources in the warm season. Cold-season ARs in the Atlantic and Pacific sectors source 73.2% and 85.3% of their moisture from their respective ocean basins at lower latitudes, while warm-season contributions decrease to 41.3% and 29.4%. In contrast, mid- and high-latitude continents combined contribute 40.1% and 51.3% in the warm season. Trajectory clustering analysis shows that AR moisture sources depend on both their genesis regions and transport pathways. In recent decades, the Arctic has experienced a moistening trend in both the cold and warm seasons. Our results suggest that local and external sources equally drive the observed cold-season moistening, whereas external sources predominantly drive the warm-season moistening. A better understanding of Arctic AR moisture sources under current climate conditions provides valuable insights into their potential future changes amid the projected heterogeneous northern hemispheric warming.