Influence of Boreal Winter Intraseasonal Variation of Aleutian Low on Water Vapor Transport and Atmospheric Rivers

Abstract

The Aleutian Low (AL) operates multiple time scales. The intraseasonal variation of AL is responsible for the subseasonal variability over the pan-North Pacific region. Atmospheric water vapor transport and atmospheric rivers (ARs) changes associated with the intraseasonal variation of AL are investigated over the North Pacific region for the winters of 1979–2014 in this study. The AL’s intraseasonal variation with a peak period of 40 days is identified. A total of 43 events that demonstrate the AL’s feature of strengthening and then weakening is picked and used for composition analysis. During the AL’s strengthening stage, eastward water vapor transport is dominant to the west of 150° W over the mid-basin. Meanwhile, poleward transport is dominant between 150–125° W. During the AL’s weakening stage, the eastward transport is weakened, and the poleward transport is concentrated over the center basin. Accompanied by the AL’s intraseasonal intensity oscillation, the frequency of ARs firstly increases, and then decreases over the ARs’ climatological mean body region over the North Pacific. The moisture source over the western North Pacific is hoarded during non-AR days, while the moisture sinks over the northeastern North Pacific during the AL’s strengthening stage, and the moisture sources over the center basin during the AL’s weakening stage converge during AR days. Hydroclimate effects on anomalies in precipitation over the west coast of North America are also analyzed.