Contrasting Windy and Wet Atmospheric Rivers: Characteristics and Variability

Atmospheric rivers (ARs) are intensive poleward moisture transport events that are essential to the global hydrological cycle and regional water resources, and are often linked to extreme weather events. We categorize the winter northern Pacific ARs by calculating the ratio between column-integrated moisture flux and column-integrated moisture to examine the distinct features between wind-dominated (windy) and moisture-dominated (wet) ARs. More windy ARs originate over the northwestern Pacific, while wet ARs prefer genesis over the northeastern Pacific. Wet ARs generally have a shorter lifetime and terminate closer to the tropics compared to total ARs. ARs account for about 50 percent of precipitation over the west coast of North America, where about 20 (10) percent of the AR-related precipitation is contributed by windy (wet) ARs. The wet ARs are positively correlated with precipitation over the Bering Sea including Alaska and northeastern Russia, and contribute about 12-15 percent of the total precipitation. We found that windy ARs are significantly modulated by El Niño Southern Oscillation, where windy ARs are more active during El Niño winters: the strong eastward wind anomaly compensates the decreased moisture due to colder sea surface temperature. Wet ARs, however, are closely correlated with the Pacific/North American teleconnection pattern, suggesting that the occurrence of wet ARs is impacted by natural variability. The robustness of the connections and variability found in reanalysis are further validated with model simulations.