Characteristics of Different Atmospheric River Types and Their Links with Extreme Precipitation over Western North America

Atmospheric rivers (ARs) can have significant socioeconomic impacts induced by heavy rainfall, flooding, and strong winds. In our study, ARs making landfall over western North America are classified into southern, northern and middle types using Self-Organizing Maps in the ERA-Interim reanalysis from 1980 to 2004. The southern type is associated with the development and eastward movement of anomalous lower pressure over the subtropical eastern Pacific, while the northern type is linked with the eastward movement of anomalous cyclonic circulation stimulated by warm sea surface temperatures over the subtropical western Pacific. The middle type is connected with the negative phase of North Pacific Oscillation-Western Pacific pattern.

The links between different AR types and the extreme precipitation at different percentiles are also investigated. The results indicate that the southern type mainly contributes to the precipitation over California, while the northern and middle types mostly lead to precipitation over Vancouver Island and Washington State. The moisture budget analysis of different AR types is also conducted to further understand how ARs contribute to the extreme precipitation.