Global Application of the Atmospheric River Scale

Atmospheric rivers (ARs) are narrow, elongated, transient corridors of enhanced water vapor transport that play important roles in the global water cycle. Increasing scientific and societal interests in ARs prompted the introduction of an AR scale (ranks 1-5, from weak to strong) initially focused on western North America. Aided by a global AR detection algorithm, the current study explores the insights the AR scale can help provide from a global perspective. It is found that AR event count is inversely related to AR rank and peaks in midlatitude oceans. Out of all precipitation occurrences, ARs account for an increasing fraction as the precipitation intensity considered increases. Over the oceans, this fraction is composed of comparable contributions from the five AR ranks, but the contribution of AR 5 is much smaller over land. Higher-ranked ARs tend to initiate at lower latitudes, terminate at higher latitudes, but follow a less sloped track due to longer zonal displacement. Sensitivity analysis indicates that if ARs are defined using a sole IVT threshold of 250 kg m(-1) s(-1) globally but with the tropics excluded, the spatiotemporal patterns of key AR event characteristics are largely similar to those described above, except AR events are more frequent by a factor of & amp;SIM;1.5-2 depending on the AR rank. The results demonstrate the potential of the AR scale in helping evaluate and communicate ARs ' influences globally, where the uniform scaling facilitates intercomparisons across different regions and the perception of impacts can be adjusted according to local climatology.

Automated summary

Atmospheric rivers (ARs) are narrow corridors of enhanced water vapor transport that play important roles in the global water cycle. The AR scale helps evaluate and communicate the global influences of ARs, with AR event count inversely related to AR rank and peaking in midlatitude oceans. As precipitation intensity increases, ARs account for a larger fraction of precipitation occurrences.