Life Cycle of Atmospheric Rivers: Identification and Climatological Characteristics

Abstract

An atmospheric river (AR) event is a strong poleward moisture transport that is composed of a series of spatiotemporally connected instantaneous AR objects. A new object‐based tracking algorithm is developed in this study, which aims to identify an AR event and investigate its life cycle from origin to termination. The algorithm identifies duration, intensity, propagation speed and direction, and the traveled distance throughout the life cycle of the AR event. The tracking algorithm is applied to 6‐hourly column‐integrated water vapor flux from November to March during the period of 1979–2017, with a focus on the North Pacific. Most North Pacific AR events originate in the subtropics over the Northwest Pacific and terminate at higher latitudes over the Northeast Pacific including western North America. On average, long AR events that last more than 72 hrs travel 7 times longer in distance and have stronger intensity than short AR events that last less than 24 hrs. Finally, a new accumulated AR intensity index is developed, which summarizes the overall impact of AR events over a given domain during a certain period by incorporating number, lifetime, and intensities of AR events.

Tracking Atmospheric Rivers Globally: Spatial Distributions and Temporal Evolution of Life Cycle Characteristics

“…As in the case of AR identification methods, it is expected that multiple AR tracking methods will coexist that complement one another and suit different applications. Besides other details, a key difference is noted between the current AR tracking method and two existing tracking methods (Sellars et al, ; Zhou et al, ), which is how separations and mergers are handled. All three algorithms recognize separations and mergers (although not explicitly studied in Sellars et al, ), but the behavior of the associated track differs among the algorithms, as illustrated in Figure for the case of merger.…”

“…A similar concept was used in Debbage et al () for tracking ARs crossing the southeastern U.S. coastline, and in Inatsu () for tracking extratropical cyclones. Other parameters/procedures being equal, it can be expected that on average the Sellars et al () algorithm will tend to yield longer‐lived tracks, the Zhou et al () algorithm shorter‐lived tracks, and the current algorithm somewhere in between.…”

Global atmospheric moisture transport associated with precipitation extremes: Mechanisms and climate change impacts

“…The resulting water-related natural hazards for each AR are also listed. evolution of ARs (Ralph, Wilson, et al, 2018;Zhou, Kim, & Guan, 2018). There are also large uncertainties of ARs and associated precipitation even detected with the same method, and greater contributions of atmospheric to regional precipitation are often implied in datasets with a higher spatial resolution (Huning, Guan, Waliser, & Lettenmaier, 2019).…”

Climate and rivers

“…At the decadal time scale, Liu, Ren, and Yang () highlight the possible importance of the Pacific Decadal Oscillation in influencing AR trajectories, whereas Gershunov, Shulgina, Ralph, Lavers, and Rutz () note important associations between Pacific sea surface temperatures and AR frequency, which may bear implications for the generally rising trend in land‐falling AR activity found in their analysis based on AR activity for the period 1948–2017. Focusing on life cycle characteristics of Pacific Northwest AR, Zhou, Kim, and Guan () distinguish between long and short AR events noting that the former last more than 72 hr, travel seven times longer in distance, and have a stronger intensity than short AR events, which last less than 24 hr. Further using life cycle characteristics, Zhou, Kim, and Guan () have developed an AR intensity index for hydrological analyses.…”

“…Focusing on life cycle characteristics of Pacific Northwest AR, Zhou, Kim, and Guan () distinguish between long and short AR events noting that the former last more than 72 hr, travel seven times longer in distance, and have a stronger intensity than short AR events, which last less than 24 hr. Further using life cycle characteristics, Zhou, Kim, and Guan () have developed an AR intensity index for hydrological analyses. That the location of AR and where they make landfall holds implications for extreme precipitation events and flooding in the United States is recognised in a climatological analysis of the inland penetration of AR over the western parts of the United States.…”